FOUS30 KWBC 071920
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
320 PM EDT Mon Apr 7 2025

Day 1
Valid 16Z Mon Apr 07 2025 - 12Z Tue Apr 08 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF
THE SOUTHEAST AND LOWER MID ATLANTIC REGION...

...1600 UTC Update...
Latest surface analysis indicates the cold front has now moved east
of the western portions of the FL Panhandle, as has the axis of
deeper convection/higher cloud tops per longwave IR associated with
the Warm Conveyor Belt (WCB). With the diminishing deep-layer
instability and negative TPW behind the front, we've been able to
remove the Slight Risk across south-central AL and the far western
portions of the FL Panhandle.

Otherwise, the Marginal Risk remains in place across parts of the
eastern Gulf Coast into the Southeast and Lower Mid Atlantic
region. The main hindrance from a flash flood perspective is the
progressive nature of the front as time marches on this afternoon
and evening. Considered a Slight Risk for areas farther east near
the Apalachicola River in FL which could see an outflow boundary
reach the region and stall while convectively active, waiting for
the cold front to catch up before picking up the pace. However, QPF
amongst the global and mesoscale guidance showed low chances for
3"+, so left the risk farther east as Marginal, which was
coordinated with the TAE/Tallahassee FL forecast office.

Hurley/Roth


Day 2
Valid 12Z Tue Apr 08 2025 - 12Z Wed Apr 09 2025

...A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS IN SOUTHERN FLORIDA...

...1930 UTC Update...
Based on the 12Z guidance, particularly the HREF and its suite of
especially the exceedance probabilities, have trimmed the Marginal
Risk a little to include far southeast FL from Homestead to West
Palm Beach. This given the anticipated frontal progression and the
fact that the bulk of the heaviest rainfall after 12Z Tue will be
east towards the northern Bahamas. 12Z model QPFs follow suit,
especially the CAMs, as the 12Z HREF probabilities of QPF greater
than 3" in 24 hours (12Z Tue-12Z Wed) now shows only a sliver of
30-40% right along the coast along and north of Pompano Beach.

...0800 UTC Discussion...
Deep southwest flow is expected ahead of an advancing cold front
across the FL Peninsula. Precipitable water values of 1.75-2" are
forecast to reside here, and ML CAPE should maximize in the
2000-3000 J/kg range per NAM guidance. Low- level inflow and
effective bulk shear are sufficient for convective organization.
Whether or not a flash flood risk fully materializes depends upon
whether or not an East Coast seabreeze front can develop and focus
convection, which could anchor convection in the large urban area
of South FL as it is unlikely to progress inland within this
synoptic pattern. In this sort of atmosphere, hourly rain totals to
2.5" and overall totals to 5" are possible. The 00z HREF does have
some non- zero probabilities of 5"+ totals across sections of the
northern Keys, while the 3"+ probabilities are more prominent along
the Gold Coast. Considering the urban environment, ingredients
available, and mesoscale guidance signal, added a Marginal Risk to
South FL and the Upper Keys as a precaution as isolated to widely
scattered flash flooding appears possible.

Roth


Day 3
Valid 12Z Wed Apr 09 2025 - 12Z Thu Apr 10 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

...Southern Illinois...
Conceptually, there is a non-zero threat of heavy rainfall in and
near southern IL Wednesday evening as precipitable water values
rise near to above 1" within a region with 1000-500 hPa thickness
near 5550 meters, implying a completely saturated troposphere. MU
CAPE is expected to rise above 250 J/kg per NAM guidance, which
tends to be under-forecast at this time range. The area will still
be attempting to dry out from recent heavy rainfall/ saturated
soils. However, there is only about a six hour window for heavy
rain concerns to materialize near the parent cyclone's associated
frontal boundary before it moves through. There is the potential
for hourly rain totals to maximize near 1.5". The guidance is this
time range QPF-wise is underwhelming, so no risk area was
depicted. However, this may change as we move closer in time into
the high resolution guidance window.


Roth
$$
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FOUS30 KWBC 090748
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
348 AM EDT Wed Apr 9 2025

Day 1
Valid 12Z Wed Apr 09 2025 - 12Z Thu Apr 10 2025

At the moment...heavy rain potential near the Florida coast
appears to be mostly offshore, except perhaps Cape Canaveral where
there is a non-zero chance of heavy rainfall within convective
banding due to onshore flow advecting in instability from the
nearby Atlantic. However, precipitable water values appear low for
atmospheric saturation, even taking into account the cooler air
mass in place. Overall, any heavy rain related issues would be
isolated at best and the probability of rainfall exceeding flash
flood guidance is considered to be less than 5 percent.

Roth


Day 2
Valid 12Z Thu Apr 10 2025 - 12Z Fri Apr 11 2025

A broad area of instability is forecast to develop across the
Lower Ohio Valley and portions of the Mid-South which shifts into
the Southern Appalachians with time. Moisture availability appears
sufficient for atmospheric saturation within a cool atmosphere
under a digging upper level trough. However, the area of sufficient moisture/moisture plume appears to be on the move. This should
limit the overall excessive rainfall/flash flood potential. The
probability of rainfall exceeding flash flood guidance may be non-
zero, but it is considered to be less than 5 percent.

Roth


Day 3
Valid 12Z Fri Apr 11 2025 - 12Z Sat Apr 12 2025

...A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF THE MID-ATLANTIC STATES AND SOUTHERN NEW ENGLAND...

A deep layer cyclone slows down as it moves across the Mid-Atlantic
States on Friday. The 1000-500 hPa thickness values are quite low
across the region, so one would only need 0.75-1" precipitable
water values to saturate the atmosphere. When combined with slow-
moving low- to mid-level frontogenesis across PA in particular,
heavy rainfall with possible areas of snow through dynamic cooling could
ensue. MU CAPE is only sufficient for issues from a vertically-
derived instability standpoint down near the VA/NC border, but
slantwise convection could be a problem for areas farther north. In
theory, hourly rain totals up to 1" with local amounts to 3" are
possible. In such situations in the past, the convective band that
forms could be quite narrow which makes placement especially
difficult to discern at this time horizon. Not helping matters are
mass field differences between the guidance as the mid- to upper-
level low is attempting to close off as the upstream ridge is
beginning to falter in strength, which would normally side against
a more southerly solution like the 00z NAM. Even so, there is
enough agreement on the heavy rain potential through the various
pieces of guidance, when combined with the ingredients above, to
maintain the Marginal Risk from continuity. Should model mass
fields converge and snow becomes less of a factor, an upgrade to a
Slight Risk may be worth considering as some areas of the northern
Mid- Atlantic States have quite low flash flood guidance (northern
NJ, west- central PA, and the Southern Tier of NY).

Roth
$$
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FOUS30 KWBC 100738
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
338 AM EDT Thu Apr 10 2025

Day 1
Valid 12Z Thu Apr 10 2025 - 12Z Fri Apr 11 2025

...OH Valley and Mid-South...
The latest GOES-E WV suite shows a mid-level trough gradually
amplifying across the Midwest as shortwave energy digs
southeastward from the northern Plains. The model guidance shows a
further amplification of mid-level height falls down across the OH
Valley and Mid-South by later today and tonight which will allow
for a cold front and an attendant area of low pressure to cross
portions of the region. Locally heavy showers and thunderstorms are
expected to develop in the warm sector this afternoon and evening
as a moderately buoyant airmass characterized by MLCAPE values of
1000 to 1500 J/kg sets up and couples with proximity of left-exit
region upper jet dynamics associated with the arrival of a jet
streak. Adding to the convective footprint will be steep mid-level
lapse rates given the amplifying trough overhead, and a sufficient
amount of shear will be in place for some supercell convection.
While moisture is not going to be particularly supportive of heavy
rainfall totals, the convection will be locally well-organized and
capable of producing some hourly rainfall totals of as much as 1 to
1.5 inches. Areas from KY/TN down through northern MS/AL will
generally see scattered pockets of this convection with this
rainfall potential. Given the wet antecedent conditions from the
most recent high-end rainfall/flooding event, it is possible that
these additional rains may result in an isolated concern for some
flash flooding. For now, a Marginal Risk will not be depicted given
some question marks on the overall coverage of convection and
modest rainfall totals, but a non-zero threat of additional
flooding will exist at least on a small-scale and highly localized basis.

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Orrison


Day 2
Valid 12Z Fri Apr 11 2025 - 12Z Sat Apr 12 2025

...A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF THE MID-ATLANTIC STATES...

...Mid-Atlantic States...
The 00Z model guidance continues to strongly support the arrival of
an amplifying deep layer trough across the central Appalachians and
the Mid-Atlantic states by Friday as an upper-level jet streak rounds
the base of the trough and lifts northeastward up across the coastal
plain. The model consensus suggests a 500mb low center developing
over the VA Piedmont area, however there is some latitudinal spread
with this as some guidance like the 00Z NAM is farther south, and
other guidance like the 00Z GFS is farther north and faster.
Regardless of exact placement, large areas of the Mid-Atlantic
region will come under left-exit region jet dynamics for ascent
which coupled with strengthening frontogenetical forcing poleward
of a deepening area of low pressure, and relatively strong moisture convergence, should promote the development and expansion of
moderate to locally heavy rainfall. Instability will be lacking
over much of the region with exception of southern VA and
especially NC where closer proximity to the warm sector will be
noted. However, there will be steepening mid-level lapse rates
associated with the closed low development, and there will be areas
of slow-moving, and rather shallow convection that will be capable
of producing heavy rainfall rates. A few model solutions such as
the GEM regional, HRW-ARW2, and NAM-Conest support locally heavy
rainfall totals (2 to 4 inches) over parts of southwest VA and NC
in particular due to slow cell-motions. Farther north into the
cooler side of the storm, the I-95 urban corridor from central VA
up into southeast PA/NJ may see locally heavy rains impact this
region with totals as high as 1 to 2 inches. Generally, these rains
should be beneficial aside from some localized urban runoff
concerns. However, there may be a more defined concern for some
localized flash flooding down into areas of southwest to south-
central VA and NC, along with some potential for southern WV to see
some of this threat. Given the southward trends in the guidance
for the overall heavy rainfall footprint, the Marginal Risk area
has been accordingly shifted farther south compared to continuity.

Orrison


Day 3
Valid 12Z Sat Apr 12 2025 - 12Z Sun Apr 13 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Orrison

$$
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FOUS30 KWBC 110800
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
400 AM EDT Fri Apr 11 2025

Day 1
Valid 12Z Fri Apr 11 2025 - 12Z Sat Apr 12 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE MID-ATLANTIC...

A slow-moving, amplifying upper level trough parked over the
eastern half of the country will direct a southerly jet streak
along the coast. This jet streak will work to cause the trough to
become more negatively tilted with time, though it will really be
neutrally tilted. Regardless, the jet streak combined with the cold
air in the trough and a developing upper-low-esque circulation in
the upper levels will support the development of a slow moving
coastal low along the Carolinas this morning. As divergence
increases and the low continues to pick up Gulf Stream moisture,
the precipitation shield will expand over much of the Delmarva west
to the I-95 corridor. For most areas, this will mean a prolonged
period of steady rainfall starting this morning and continuing well
into Friday night.

Cool air will be a feature of this low, so much of the rain will be
a windy, cold rain. This does not favor much in the way of
convective activity, which will limit rainfall rates. Any upper
level instability will remain over VA and NC, with little getting
any further north than the DC Metro. Given the lack of instability
and ongoing longer-term drought, and the eastward shift in the axis
of heaviest rainfall in the comma-head/cold sector of the storm,
the inherited Marginal Risk was trimmed out of PA and NJ due to
lack of instability, as well as trimmed out of southwest VA and
western NC. The heaviest rain is currently expected along and east
of the I-95 corridor, so it's in this area where the Marginal
remains in place.

Wegman


Day 2
Valid 12Z Sat Apr 12 2025 - 12Z Sun Apr 13 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman


Day 3
Valid 12Z Sun Apr 13 2025 - 12Z Mon Apr 14 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman

$$
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FOUS30 KWBC 140804
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
404 AM EDT Mon Apr 14 2025

Day 1
Valid 12Z Mon Apr 14 2025 - 12Z Tue Apr 15 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
WEST VIRGINIA...

A Marginal Risk area for much of the central and southern regions
of West Virginia was introduced with this update. The latest CAMs
guidance continues to hint at a line of training showers and
thunderstorms that will press southeastward this afternoon and
evening, while the storms move more eastward, suggesting at least
some potential for training. The biggest question will be how
strong the storms with the heaviest rain cores will get. A few of
the CAMs, such as the NAMnest, 00Z HRRR and, GEM Regional all
suggest there will be a line of training storms, albeit in
different areas of the state. Thus, as is typical with Marginals,
the area is likely far bigger than the portions of the state that
end up actually seeing flash flooding. Given the aforementioned
uncertainty, the area is bigger to account for that. MUCAPE values
will be around 500 J/kg this afternoon, and PWATs will be between 1
and 1.25 inches, which are values that should support the isolated
flash flooding threat consistent with a Marginal Risk, given the
general agreement for limited areas of training.

Wegman


Day 2
Valid 12Z Tue Apr 15 2025 - 12Z Wed Apr 16 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman


Day 3
Valid 12Z Wed Apr 16 2025 - 12Z Thu Apr 17 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
NORTHERN CALIFORNIA AND WESTERN NEVADA...

An upper level low centered off the coast of central California
Wednesday morning will drift eastward towards the coast through the
day. This upper low will spread increasingly cold air in the upper
levels over California and Nevada. This will increase the
instability over the region. Meanwhile, a plume of Pacific moisture
will also move into the region, raising PWATs above 0.75 inches in
some areas, which is over 2 sigma above normal and above the 95th
percentile compared to climatology for the region. Finally,
plentiful warm air in the lower levels of the atmosphere will both
contribute to that instability, as well as raise snow levels to
9-10k ft, so the vast majority of expected precipitation in and
around the Sierras will be in the form of rain. Since expected
MUCAPE values will increase to around 500 J/kg over the area, the
storms that form will be capable of producing cores of heavier
rain, which combined with snowmelt in the Sierras will support an
isolated flash flooding risk, especially in the most prone valleys
and low lying areas. Thus, in coordination with REV/Reno, NV and STO/Sacramento, CA forecast offices, a Marginal Risk was
introduced with this update. Expect with changing model guidance
that the Marginal area will shift between the morning model run
cycle and Wednesday's event, particularly across western Nevada, as
the amount of convection that may cross the Sierras becomes more
clear.

Wegman

$$
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FOUS30 KWBC 151433
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1033 AM EDT Tue Apr 15 2025

Day 1
Valid 16Z Tue Apr 15 2025 - 12Z Wed Apr 16 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman


Day 2
Valid 12Z Wed Apr 16 2025 - 12Z Thu Apr 17 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
NORTHERN CALIFORNIA AND WESTERN NEVADA...

A slow-moving upper level low embedded within a broader positively
tilted trough will move towards the central California coast on
Wednesday. The associated upper level cold air will overspread
central California with sufficient surface heating to increase
instability along the Sierras to between 500 and 1,000 J/kg. The
upper low will also bring a bit of Pacific moisture into the region
as PWATs increase to between 0.5 and 0.75 inches, which for central
California is as much as 3 sigma above normal and exceeds the 95th
percentile for climatology. Corfidi Vectors will generally be out
of the north to northeast, which will favor south to southwest
moving convection developing on the Nevada side of the Sierras then
slowly moving over or along the range into the foothills of the
Central Valley. Given this setup, there is potential for training
convection since all of the factors that are coming together to
support heavy rainfall from the stronger storms will be slow-moving
and persist through the afternoon and evening hours. Snow levels
from the NBM Wednesday afternoon will be between 8,000 and 9,000
ft, allowing most of the precipitation that falls to be in the
form of rain except at the highest elevations of the Sierras.
Abundant snowpack also remains in place in the Sierras below the
melting level, which will allow for some contribution to rising
streams and creeks to be from snowmelt. Thus, an isolated flash
flooding risk remains in this area. The inherited Marginal risk was
trimmed on the edges, especially into western Nevada, since the
storms will generally track towards California. However, no big
changes were made with this update.

Wegman


Day 3
Valid 12Z Thu Apr 17 2025 - 12Z Fri Apr 18 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTHWESTERN UTAH...

The upper level low causing the marginal risk of excessive rainfall
in northern California on Day 2/Wednesday will open up and become
an extension of a longwave positively tilted trough over much of
the West on Thursday. The low-turned-trough will accelerate
eastward into southern California and eventually Arizona by late
Thursday night. The energy associated with it will draw a more
substantial upper level shortwave south into the Intermountain West
Thursday and Thursday night. The advance of the associated cold
air will increase the lift ahead of the front. Some of the Pacific
moisture will draw northeastward into southwestern Utah ahead of
the front, supporting more widespread rainfall across the region,
especially Thursday evening into the overnight. While associated
rainfall rates through here are unlikely to exceed a half inch per
hour in any one area for an extended period of time, this rain
falling on very dry and hydrophobic soils are likely to convert
mostly to runoff. Typical flooding locations such as slot canyons
will be at greatest risk for flash flooding. The rainfall should
not be enough to cause widespread flash flooding, but is likely to
cause isolated flash flooding. While higher elevations of Utah may
see mostly snow from this front, once again most areas should
remain as rain.

Wegman

$$
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FOUS30 KWBC 160804
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
404 AM EDT Wed Apr 16 2025

Day 1
Valid 12Z Wed Apr 16 2025 - 12Z Thu Apr 17 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

The inherited Marginal Risk for portions of the Sierras of northern
California was removed with this update. The upper low is a bit
weaker with less moisture than in previous forecasts, resulting in
lowering amounts of rainfall forecast across this region. Thus,
despite some support from snowmelt, isolated flash flooding is no
longer anticipated in this region.

Wegman


Day 2
Valid 12Z Thu Apr 17 2025 - 12Z Fri Apr 18 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

The inherited Marginal Risk for portions of southwestern Utah was
removed with this update. In addition to decreasing forecasts for
precipitation in this region, falling snow levels should keep a
significant portion of the precipitation that falls at the higher
elevations as snow, and therefore will not contribute to any
isolated flash flooding. The threat can't be entirely ruled out
even given these changes for slot canyons and flood prone areas,
but has come down to between 0 and 5 percent.

Wegman


Day 3
Valid 12Z Fri Apr 18 2025 - 12Z Sat Apr 19 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
CENTRAL AND NORTHEASTERN OKLAHOMA INTO SOUTHWESTERN MISSOURI...

A large and very positively tilted longwave trough extending from
the Northern Plains down into the Southwest/4 Corners Region will
slowly press eastward towards the Southern Plains on Friday. As
this forcing encroaches across the Plains, it will run into a very
well established southwesterly LLJ extending from the far western
Gulf (and really the Caribbean before that) northward across
central Texas and then northeast into the Midwest. For much of the
day Friday, the forcing to the west and the LLJ will be
sufficiently separated so as to not result in much precipitation
over the Slight Risk area. However, come late Friday afternoon
through the overnight, that will change as the longwave trough
moves east and an embedded shortwave rides the base of the trough
and digs eastward, locally increasing the upper level divergence
(and therefore forcing), needed to initiate and maintain both
convection and a broader rainfall shield around it. Thus, expect
thunderstorms to break out along and ahead of the jet with a
supporting surface cold front slowly pushing southeastward.

As the LLJ runs into the front, storms will rapidly develop
northeastward along the front, then train northeastward one after
another as the LLJ restores the moisture used up by the storms in
the form of heavy rainfall. There is good agreement that the I-44
corridor from Tulsa to Joplin will be the area at greatest risk for
heavy rainfall through Friday night, though storms may continue to
backbuild down to the Oklahoma City metro, and will persist
eastward towards St. Louis. There is good agreement in the guidance
that this scenario will unfold, but less agreement on where this
corridor of training storms will set up, with the I-44 corridor
being the broader consensus. Thus, expect the Slight Risk area to
shift with future updates. Should this corridor shift
southeastward, the heaviest rain will align better with the area
hard hit by the historic rainfall just 2 weeks ago, and while
conditions have significantly improved due to the recent dry
weather, a repeat hit may cause worsened impacts with recovery
still occurring in the area. It's possible a further upgrade to a
Moderate Risk may be necessary with future updates. However, should
the corridor remain along I-44, urban concerns in Tulsa, Joplin,
and the Fayetteville/Bentonville area may locally increase the
impacts from the heavy rain.

Wegman

$$
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FOUS30 KWBC 170800
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
400 AM EDT Thu Apr 17 2025

Day 1
Valid 12Z Thu Apr 17 2025 - 12Z Fri Apr 18 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
MINNESOTA AND WISCONSIN...

A Marginal Risk upgrade was introduced with this update for
portions of Minnesota and Wisconsin. Surface troughing associated
with a developing low over the Plains will strengthen today as a
potent cold front with much colder air moves in from the Canadian
Prairies. It will run into a potent southerly LLJ with 850 winds as
high as 35 kt advecting some Gulf moisture with PWATs up to 1.25
inches into the region. The combination of the influx of moisture
and strong forcing is expected to cause showers and storms to break
out at the nose of the jet starting this afternoon. The storms will
be fast moving, but the LLJ will supply additional moisture so that backbuilding and training storms will be possible before the storms
congeal into more of a line, which will limit the potential for
training from then on. The greatest concern for isolated flash
flooding will be in the Twin Cities metro area, where urban
concerns and lower FFGs may be exceeded if the storms train over
the cities. HREF probabilities for exceedance of 3 hour FFGs peak
above 60 percent in the Twin Cities between 21Z/4pm CDT and 00Z/7pm
CDT. Along with reasonably good CAMs guidance agreement on the
development of storms in that general area, this prompted the
Marginal Risk issuance.

Wegman


Day 2
Valid 12Z Fri Apr 18 2025 - 12Z Sat Apr 19 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR NORTHEASTERN
OKLAHOMA THROUGH CENTRAL MISSOURI...

A well-established and persistent southerly LLJ will be parked
across much of the middle of the country Friday into Friday night.
Deep tropical moisture originating from the Caribbean will flow
into the Texas Gulf Coast and along a very slow moving frontal zone
draped across the Plains to the upper Great Lakes. Showers and
thunderstorms will likely break out during peak heating across the
region starting during the late afternoon hours, but the strongest
storms and greatest rainfall are more likely to occur overnight
Friday night. The strong cold front to the north will run into
opposing flow from the LLJ, causing its progression south and east
to slow as it approaches Oklahoma and Missouri from the northwest.
This will act as a wall, resulting in the LLJ air mass to ride up
and into the front, then track along the frontal interface to the
northeast. This classic frontal scenario will strongly support
training thunderstorms that individually may move quickly to the
northeast as the LLJ intensifies to 50 kt over northwestern
Arkansas Friday night. However, the steady influx of moisture will
support backbuilding along the front, resulting in a line of
training storms across this area. The rain will be somewhat offset
from the area of greatest historic rainfall from 2 weeks ago, and
the smaller streams and creeks have fully drained from that event,
but the bigger rivers, including the Missouri, Arkansas, and
Mississippi continue to drain, and this new influx of rainfall
could back up as the new rainfall meets already full rivers. The
bulk of the event will focus into the Day 3 period. With greater
instability available for the storms to produce heavy rainfall
during this period, it's likely that where the storms are most
persistent, there will be widely scattered instances of flash
flooding, especially near the Tulsa and Joplin metros.

Guidance has favored a very small (roughly 5-10 mile) trend
towards the northwest with each run, so the Slight Risk area was
expanded a row of counties north and west with this update, but
otherwise no big changes were made. The greatest uncertainty lies
in the southwestern extent of the axis of heaviest rainfall, so a
small adjustment to the Red River (TX/OK border) was also made with
this update. In coordination with PAH/Paducah, KY and ILX/Lincoln,
IL forecast offices, the Marginal Risk was also expanded south and
east to account for the new rainfall interacting with still
draining rivers from 2 weeks ago into far southeastern Missouri and
southern Illinois as well.

Wegman


Day 3
Valid 12Z Sat Apr 19 2025 - 12Z Sun Apr 20 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FROM EASTERN
OKLAHOMA THROUGH MUCH OF SOUTHERN MISSOURI...

In coordination with the impacted forecast offices, a Moderate Risk
upgrade was introduced with this morning's ERO update. A stationary
front separating very warm and moisture-laden air to the south from
abnormally cold air to the north will stall out from being a cold
front in previous days. Weakening northeasterly flow of cold, dry
air on the north side of the front, spurred on by a Canadian high
over the Great Lakes will contrast with an ever increasing supply
of hot and humid air straight out of the Gulf being advected
northward on up to 50 kt winds across Texas and into the frontal
interface from north Texas through Oklahoma and Missouri. Meanwhile
in the upper levels, a potent shortwave, previously an upper level
low will eject eastward out of the mountains and into this warm and
humid air mass. This will result in cyclogenesis across Oklahoma by
Sunday morning. Until that happens though, the front will be
largely stationary, with the warm humid air tracking northeastward
on one side, and cool, dry air tracking southwestward on the cold
side. The abundance of moisture and cold pools from Friday night's
storms will support continued shower and thunderstorm development
south of the front. As the shortwave approaches, additional shower
and thunderstorm development will occur, and with stronger storms
due to the added forcing as the surface low develops to the west.

The southerly flow of humid air will cause the storms to run into
the Ozarks of Oklahoma, Arkansas, and especially southern Missouri
on Saturday. The mountains will further uplift the moisture,
resulting additional locally heavy rainfall. The Ozarks are known
for being particularly flash flood prone due to the mountains
helping funnel the water quickly into the river valleys, so this
prolonged period of heavy rainfall is likely to cause some of the
worst impacts to occur in these regions.

As the storms track northeastward across Missouri, the front is
likely to direct them into the St. Louis metro. In coordination
with LSX/St. Louis forecast office, the Moderate Risk's
northeasternmost extent includes the St. Louis metro. While the
storms may not be quite as strong as compared with areas further
south and west by the time they reach St. Louis, the urban corridor
and confluence of major rivers in the area may exacerbate urban
flooding concerns as repeated rounds of heavy rain likely move over the city.

Some of the guidance (RRFS/UKMET/CMC) are favoring the southern end
of the ERO risk areas across Texas and Oklahoma as being the area
with the heaviest rain. Should that occur, then, the Dallas-Fort
Worth Metroplex will also be at higher risk for flash flooding, and
the Moderate Risk may need to be expanded southwestward with future
runs. There were 2 camps of guidance, largely split between foreign
and domestic, favoring the southern and northeastern ends
respectively. To account for these factors, the Slight and Marginal
Risk were expanded northeastward along the frontal interface to the
IL/IN border for the Slight, and well into northern Ohio for the Marginal.

Wegman

$$
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FOUS30 KWBC 180805
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
405 AM EDT Fri Apr 18 2025

Day 1
Valid 12Z Fri Apr 18 2025 - 12Z Sat Apr 19 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR NORTHEASTERN
OKLAHOMA THROUGH CENTRAL MISSOURI...

A persistent southerly low-level jet transporting deep tropical
moisture into the Texas Gulf Coast and along a very slow moving
frontal zone draped across the Plains to the upper Great Lakes will
lead to the development of convection during peak heating. However,
the strongest of the storms will likely be during the late evening
and overnight hours. The strong cold front to the north will run
into opposing flow from the LLJ, causing its progression south and
east to slow as it approaches Oklahoma and Missouri from the
northwest. This will act as a wall, resulting in the LLJ air mass
to ride up and into the front, then track along the frontal
interface to the northeast. This setup will be favorable for
training of thunderstorms and some of the individual cells may
advance quickly to the northeast as the low-level jet intensifies
to 50 kt over northwestern Arkansas Friday night.

The rain will be somewhat offset from the area of greatest
historic rainfall from 2 weeks ago, and the smaller streams and
creeks have fully drained from that event, but the bigger rivers,
including the Missouri, Arkansas, and Mississippi continue to
drain, and this new influx of rainfall could back up as the new
rainfall meets already full rivers. The bulk of the event will
focus into the Day 2 period. With greater instability available
for the storms to produce heavy rainfall during this period, it's
likely that where the storms are most persistent, there will be
widely scattered instances of flash flooding, especially near the
Tulsa and Joplin metros. A Marginal Risk area spans from the
vicinity of the Oklahoma/Texas border northeastward to
Illinois/Indiana. The Slight Risk was adjusted a small amount to
the west than the previous forecast.

Campbell

Day 2
Valid 12Z Sat Apr 19 2025 - 12Z Sun Apr 20 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FROM NORTH-
CENTRAL TEXAS THROUGH MUCH OF SOUTHERN MISSOURI...

A stalled boundary will lead to a stark gradient between two
airmasses, on
with some adjustments on the day shift cycle to pull it a little
more south into the Lower Mississippi Valley along the front where
the better instability should be located. e abnormally cool for mid-April and the rich in
moisture. On the north side the cold, dry northeasterly flow will
be weakening while in the warm sector there will be an ever
increasing supply of hot and humid air straight out of the Gulf
being advected northward on up to 50 kt winds across Texas and into
the frontal interface from north Texas through Oklahoma and
Missouri. Meanwhile in the upper levels, a potent shortwave,
previously an upper level low will eject eastward out of the
mountains and into this warm and humid air mass. This will result
in cyclogenesis across Oklahoma by Sunday morning. Until that
happens though, the front will be largely stationary, with the warm
humid air tracking northeastward on one side, and cool, dry air
tracking southwestward on the cold side. The abundance of moisture
and cold pools from Friday night's storms will support continued
shower and thunderstorm development south of the front. As the
shortwave approaches, additional shower and thunderstorm
development will occur, and with stronger storms due to the added
forcing as the surface low develops to the west.

The westward trend of QPF persisted into this time period, placing
the highest amounts over far north-central Texas, southwest and central Oklahoma. A narrow swath of amounts 3 inches or greater are
expected in this part of the region. The storms to run into the
Ozarks of Oklahoma, Arkansas, and especially southern Missouri on
Saturday. The mountains will further uplift the moisture, resulting
additional locally heavy rainfall. As the storms track
northeastward across Missouri, the front is likely to direct them
into the St. Louis metro. In coordination with LSX/St. Louis
forecast office, the Moderate Risk's northeasternmost extent
includes the St. Louis metro. While the storms may not be quite as
strong as compared with areas further south and west by the time
they reach St. Louis, the urban corridor and confluence of major
rivers in the area may exacerbate urban flooding concerns as
repeated rounds of heavy rain likely move over the city.

The Moderate Risk area was expanded west/southwest further into
north-central Texas. The Slight Risk was shifted into central Texas
and the Marginal Risk had minor expansions to the west. With the
overall western shift of all of the Risk thresholds, the eastern
bounds of each were trimmed back to the west as well.

Campbell/Wegman


Day 3
Valid 12Z Sun Apr 20 2025 - 12Z Mon Apr 21 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR THE CENTRAL
PLAINS AND PORTIONS OF THE MIDDLE AND LOWER MISSISSIPPI VALLEY...

The upper trough and surface low pressure system will continue to
spread showers and thunderstorms across the central U.S. Sunday as
it lifts northeastward. The amount of moisture and instability may
be reduced when compared to Saturday, however it will likely be
above normal. The nature of the low track and associated storms are
expected to be a little more progressive which should limit
rainfall accumulations. Additionally, the bulk of the higher
rainfall amounts is forecast to largely fall north of the Saturday
footprint. A Marginal Risk is in place for the Middle and Lower
Mississippi Valley and eastern portions of the Central Plains.
These areas are north and west of the most sensitive areas of the Mississippi/Ohio River Valleys where streamflows remain high after
recent flooding. However, some rain atop recently flooded areas,
and runoff from other areas into these rivers, could exacerbate
ongoing flooding issues in some areas, so continue to monitor.

Campbell

$$
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FOUS30 KWBC 190754
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
354 AM EDT Sat Apr 19 2025

Day 1
Valid 12Z Sat Apr 19 2025 - 12Z Sun Apr 20 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FROM NORTH-
CENTRAL TEXAS THROUGH MUCH OF SOUTHERN MISSOURI...

A narrow corridor of 4 to 6+ inches of rainfall likely today
across southern Missouri to North-central Texas as thunderstorms
train and backbuild along a slow moving/stalled frontal boundary.
There has been a consistent and persistent westward trend of the
placement of the heaviest rainfall both in the model runs and the
deterministic WPC QPF. Once again the risk areas were expanded
south and west. The Moderate Risk spans from north-central Texas to
the Missouri Ozarks; which had a minor reduction in coverage out of
Illinois given the decrease in QPF from the Mid-Mississippi Valley
to Ohio. The Slight Risk was also reduced over parts of Illinois
and Indiana while extended further into central Texas. The Marginal
was trimmed southward across Illinois, Indiana and Ohio while
adjusted westward of west-central Texas.

On the north side the cold, dry northeasterly flow will be
weakening while in the warm sector there will be an ever increasing
supply of hot and humid air straight out of the Gulf being
advected northward on up to 50 kt winds across Texas and into the
frontal interface from north Texas through Oklahoma and Missouri.
An upper low ejecting from the mountains into this hot, moist
airmass will lead to robust cyclogenesis over Oklahoma by Sunday
morning.

Campbell


Day 2
Valid 12Z Sun Apr 20 2025 - 12Z Mon Apr 21 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR THE CENTRAL
PLAINS AND PORTIONS OF THE MIDDLE AND LOWER MISSISSIPPI VALLEY...

The system responsible for the scattered to widespread
heavy/excessive rainfall on Saturday will begin to accelerate to
the northeast as the upper trough begins to fill. Rainfall amounts
should not rival amounts that are expected on Saturday, but
additional rainfall on top recently flooded areas remains a
potential concern. General model consensus shows a broad footprint
of up to 1.25 inches with isolated maximums of 1.5 to 2+ inches
anywhere from eastern Nebraska to southern Minnesota and Wisconsin.
The exact location of the heaviest amounts has the greatest
uncertainty.

A Marginal Risk is in place for the Middle and Lower
Mississippi Valley and eastern portions of the Central Plains.
These areas are north and west of the most sensitive areas of the Mississippi/Ohio River Valleys where streamflows remain high after
recent flooding. However, some rain atop recently flooded areas,
and runoff from other areas into these rivers, could exacerbate
ongoing flooding issues in some areas, so continue to monitor.

Campbell/Bann


Day 3
Valid 12Z Mon Apr 21 2025 - 12Z Tue Apr 22 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Campbell

$$
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FOUS30 KWBC 200829
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
429 AM EDT Sun Apr 20 2025

Day 1
Valid 12Z Sun Apr 20 2025 - 12Z Mon Apr 21 2025

..THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS THE CENTRAL
US TODAY INTO TONIGHT...

Introduced a Slight Risk area for the potential of excessive
rainfall from parts of Texas into the Upper Midwest/Northern
Plains. It is really a composite of multiple reasons to warrant a
Slight Risk area in different geographical areas. The northern
portion of the Slight Risk area covers the growing model signal for
2-3+ inches of rain due to a combination of deformation
zone/surface low and good divergence aloft from the highly curved
anticyclonic upper level jet all becoming more or less collocated.
Rainfall amounts in the central part of the US are forecast to be
less than areas to the north...but the Slight Risk area was more
targeted for overlap between future rainfall on top of what MRMS
has shown for the past 24-36 hrs in anticipation of how the FFG
values will change. Lastly...kept some parts of the Southern Plains
in an outlook area based on short term radar/satellite trends.
While rates have come down as the plume of highest equivalent
potential temperature has narrowed overnight...suspect that the
potential for at least some excessive rainfall will persist beyond
the start of Day 1 period at 20/12Z. Those areas can be removed in
the mid- morning Day 1 ERO assuming that trends continue downward.

Bann


Day 2
Valid 12Z Mon Apr 21 2025 - 12Z Tue Apr 22 2025

The probability of rainfall exceeding Flash Flood Guidance is less
than 5 percent.


Bann

Day 3
Valid 12Z Tue Apr 22 2025 - 12Z Wed Apr 23 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF TEXAS AND/OR THE ADJACENT SOUTHERN PLAINS...

Largely maintained a Marginal Risk area over portions of the
Southern Plains from Tuesday into early Wednesday morning due to
the suite of 00Z numerical guidance continuing to show the
potential for repeat/training of cells during the day and with
overnight activity within an emerging moist and unstable return
flow into and over several frontal boundaries. With the models
struggling to latch onto a coherent signal...as shown by some
guidance focusing heaviest QPF near the Gulf coast in proximity to
a weakening cold front and other guidance developing the threat
closer to the Red River in response to the approach of a mid-level
wave...have opted to highlight concern for excessive rainfall in
broad and rather unfocused Marginal Risk area close to a consensus
placement of the precipitable water axis. With PW values generally
being 1.25 inches or less...would not be expected numerous
torrential downpours. The cumulative effect of what has already
fallen from this weekends event and what falls on Tuesday/early
Wednesday needs to be watched.

Bann

$$
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FOUS30 KWBC 210808
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
408 AM EDT Mon Apr 21 2025

Day 1
Valid 12Z Mon Apr 21 2025 - 12Z Tue Apr 22 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS SOUTHEAST
TEXAS AND PORTIONS OF THE DEEP SOUTH...

Low-level confluence has aided in persistent, slow-moving
convection across southeast Texas and near Shreveport
overnight/early Monday. Models suggest that these storms should
continue within a similar regime for at least a few hours early in
the forecast period (through 18Z or so) as low-level confluence
shifts southward. Moist/unstable air (1.75+ PWATs) should be
maintained ahead of the activity, which should support local 2
inch/hr rainfall amounts at times given expected slow storm
motions. An instance or two of flash flooding is possible where the
downpours can fall over sensitive/low-lying ground conditions.

Across Mississippi and Alabama, a cold front is expected to make
southeastward progress during the day, but stall across northern
portions of both states. Models are in agreement that scattered
convective activity will develop during the afternoon/evening -
supported both by surface heating and low-level warm advection.
Some of the higher resolution guidance has tended to focus
convection from east-central MS into central AL - a scenario that
may favor training and a locally higher threat for flash flooding
especially given lower FFGs across AL/near the Birmingham area.
This scenario is a bit uncertain in placement, however, given the
overall weak forcing. A broad Marginal risk area is maintained for
this outlook to account for potential for localized 1-2 inch hourly
rain amounts that threaten local FFGs.

Cook


Day 2
Valid 12Z Tue Apr 22 2025 - 12Z Wed Apr 23 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS NORTHWEST
TEXAS AND WESTERN OKLAHOMA...

A return-flow regime begins in earnest during the forecast period
across the southern Plains and results in areas of 60s dewpoints
across the OK/TX Red River Valley area. Meanwhile, weak west-
southwesterly mid-level flow and weak perturbations within that
flow should spark initially higher-based thunderstorm activity
across the Panhandles that should spread east-southeastward toward
areas of greater moisture content after 00Z. The outflow dominant
nature of initial storms should limit flash flood potential
initially, with a conditional risk materializing later in the
evening and overnight hours if 1) any upscale growth into one or
two mesoscale convective complex can promote training and boost
rain rates and 2) heavier rainfall can materialize across portions
of north-central Texas/southern Oklahoma that received 3-8 inches
of rain in the past 72 hours or so. These factors reflect a flash
flood threat that is too conditional for anything beyond
Marginal/5% probabilities at this time, and are highly dependent on
a mesoscale evolution that remains uncertain at this time.

Across North Carolina, models suggest that surface heating along
and south of a cold front near the NC/VA state line could provide a
focus for scattered thunderstorm activity during the afternoon
hours. Zonal flow aloft (parallel to this boundary) would support
some potential for convective training, although the coverage of
storms is a bit uncertain given modest ascent/mid-level support. A
Marginal Risk/5% area may be needed in later outlooks pending
greater certainly on convective evolution.

Cook


Day 3
Valid 12Z Wed Apr 23 2025 - 12Z Thu Apr 24 2025

Substantial uncertainty exists for this outlook. Broad, western
U.S. troughing aloft should result in southwesterly flow aloft
across the High Plains for much of the forecast period. Meanwhile,
southerly low-level flow should gradually moisten low-levels across
Kansas and vicinity - especially in the latter half of the
forecast period. Subtle waves within the flow aloft should promote
scattered, initially high-based thunderstorm activity during the
afternoon and early evening, though coverage and location is in
question. Thereafter, there are hints that upscale growth of
storms could result in gradually increasing heavy rain potential as
low-level warm advection results in higher moisture content/PW
values (1-1.5 inches) across central Kansas into central Oklahoma.
Again, this scenario is uncertain given pre-existing moisture
quality concerns.

Given the uncertainty and dry antecedent soil conditions,
probabilities for excessive rainfall are removed for this outlook
across the Great Plains.

Cook

$$
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FOUS30 KWBC 221208
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
808 AM EDT Tue Apr 22 2025

Day 1
Valid 12Z Tue Apr 22 2025 - 12Z Wed Apr 23 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE TEXAS PANHANDLE INTO WESTERN OKLAHOMA AND THE CENTRAL GULF
COAST INTO THE SOUTHEAST...

12z Update: The Marginal risk was expanded over the Southeast and
now stretches from LA northeastward into portions of MS/AL and the
southern Appalachians. Convection near a stalled boundary will be
capable of producing heavy rainfall rates today across this
corridor. See MPD 147 for more info on the near term possible
flash flood risk across portions of northern MS and AL.

Chenard

...Previous Discussion...

...Texas and Oklahoma...

A west-east orientated warm front paired with a dryline over West
Texas will maintain an environment conducive for convection through
the night. An expeditious shortwave ejecting out of the Southern
Rockies will navigate over the Caprock aiding in focused mid-level
ascent within the confines of the boundary and relative instability
maximum situated near the front and points south and east.
Scattered convection will likely billow up off the eastern New
Mexico Caprock down into the Stockton Plateau leading to strong
mesoscale cores maintaining a prevalent convective footprint over
the Southern Plains.

Cell propagation will be east to southeast motions given the
850-250mb shear field, entering into fairly unstable environments
downstream that will be capable of holding the convective pattern
well into the evening. Precipitable water values will be 1+
deviations above season average which could yield hourly rates of
1-2 inches/hour. These types of setups tend to be tricky, but the
setup is historically one that favors isolated flash flood
concerns, especially within any urbanized areas across the Caprock
into the western Red River Basin. The inherited Marginal Risk
continued to highlight the region with an elevated threat for heavy
rainfall and flash flooding.

...Gulf Coast...

Convection will focus along the slow-moving frontal boundary over
the Lower Mississippi Valley, particularly across southern
Louisiana. Locally heavy rain with cores generally anchored to any
remnants of the front as it decays within the southern Parishes of
the state. Several CAMs indicated a heavy rainfall footprint from
the Texas/Louisiana border to the New Orleans metro area. The
flooding threat is modest at best due to the uncertain nature of
where the pulse convective regime will initiate, however the
individual totals being depicted via CAMs (5-8") and some global
deterministic (3-5") are very much capable of causing some flash
flood concerns across the area. A Marginal Risk remains in effect
for this portion of the state, with only minor reshaping from the
previous issuance.

Campbell/Kleebauer


Day 2
Valid 12Z Thu Apr 24 2025 - 12Z Fri Apr 25 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE CENTRAL AND SOUTHERN PLAINS...

Several shortwaves will be exiting the Rockies throughout the day
with several pockets of convective development sprawled across the
Central and Southern High Plains by the evening hours. While the
confidence continues to be lower on the maximum amounts there is
however higher confidence on the potential for scattered flash
flood prospects. Although the location of QPF maxima vary, there
is a general consensus of a widespread 1 to 2 inches from the Front
Range of Colorado/Wyoming/Nebraska south to the Red River Basin
near Texas to Kansas/Oklahoma. Some of these areas will have seen
significant rainfall prior to any additional impacts leading to
some localized lower FFG indices once the event occurs. The
inherited Marginal continued to mostly highlight areas across the
Plains that had an elevated threat for heavy rainfall and flash
flooding. The latest guidance and WPC QPF trended higher with QPF
over northeast Kansas, southern Nebraska, southwest Iowa and
northwest Missouri. As such, the Marginal Risk area was modified to
encompass that part of the region.

Campbell/Kleebauer


Day 3
Valid 12Z Thu Apr 24 2025 - 12Z Fri Apr 25 2025

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
KANSAS, OKLAHOMA, ARKANSAS AND MISSOURI...

The pattern will be favorable for multiple rounds of showers and
thunderstorms to move through the south-central U.S. With a moist,
unstable flow expected and shortwave energy passing through heavy
rainfall will likely develop across the region which may lead to
local flash flooding. Areal averages of 1 to 2 inches are forecast
with locally higher amounts possible. A Slight Risk for excessive
rainfall is in effect for a large portion of Kansas, northern
Oklahoma, far northwest Arkansas and western Missouri. A Marginal
Risk area spans from northern Texas to southern Nebraska and
extreme southwest Iowa.

Campbell
$$
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FOUS30 KWBC 230759
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
359 AM EDT Wed Apr 23 2025

Day 1
Valid 12Z Wed Apr 23 2025 - 12Z Thu Apr 24 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE PLAINS AND THE SOUTHEAST...

Persistent Gulf moisture advecting northward through the Gulf
states over a stalled frontal boundary draped across the Southeast
will continue to produce scattered to widespread convection capable
of producing heavy rainfall. Rounds of showers and thunderstorms
will fire up along the the boundary from Texas to the Carolinas
with some training and backbuilding expected. Given there will be
very little movement of the front the storms are likely to track over
many of the same areas being impacted by ongoing showers and
storms of late, which locally increases the flash flooding risk. A
convective complex tracking east across the Hill Country during
the very early hours of Wednesday is spreading 0.5 to 1 inch/hour
rain rates along its path which may lead to isolated urban flash
flooding. Refer to WPC mesoscale precipitation discussion #160 for
more details.

The latest guidance has better confidence that the wettest areas
will likely focus over southern Nebraska and northern Kansas. This
too will be the result of an MCS or clusters of thunderstorms
developing and training multiple times over the same areas. The
Marginal remains in place as the consensus of heaviest rains on the
order of 1-2 inches (locally higher, of course) is in a portion of
Kansas and Nebraska that has largely missed out on recent heavy
rainfall, and the antecedent dry conditions should help to offset
and delay the greatest impacts from any heavy rain.

The area of the Marginal of least concern appears to be over
Oklahoma, which while seeing some scattered shower and thunderstorm
activity, should be between the MCSs/areas of more organized and
persistent convection. However, due to heavy rainfall, lower FFGs
over much of the state lower the threshold needed to achieve flash
flooding, so the Marginal is largely unchanged there.

Campbell/Wegman


Day 2
Valid 12Z Thu Apr 24 2025 - 12Z Fri Apr 25 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
KANSAS, OKLAHOMA, ARKANSAS AND MISSOURI...

Multiple clusters of thunderstorms will likely be ongoing in
different portions of the ERO risk areas at the start of the Day
3/Thursday time period. These MCS's will likely weaken and
dissipate through the late morning, as MCS's typically do. However,
with peak heating and the increased instability there will be
renewed rounds of showers and thunderstorms. Since this is likely
to occur over many of the same areas hit with recent heavy rain
this will once again renew the potential for localized flash
flooding over portions of the Southeast. Much of the guidance has
areal averages of 1 to 2 inches with higher maximums possible
falling over much of the same footprint in the day(s) prior. The
potential for a new MCS to form Thursday night will keep the
threat for flash flooding elevated. The inherited Slight Risk
remained largely untouched as it continued to reflect the areas
with the greater threat for flash flooding.

In similar fashion as Day 1, the low level jet will keep a steady
influx of Gulf moisture over the stalled boundary which will
maintain support for heavier rainfall with the strongest storms,
and greater coverage of showers and storms in general. A Marginal
Risk covers the northern Gulf states and Southeast.

Campbell


Day 3
Valid 12Z Fri Apr 25 2025 - 12Z Sat Apr 26 2025

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL MID-MISSISSIPPI VALLEY/Tennessee VALLEY TO PORTIONS OF THE NORTHEAST...

Recent and ongoing rainfall over some portions of this broad
region will make some areas susceptible to additional rains. During
this period a surface low pressure system and its attendant front
will likely track from the Mississippi Valley toward the Great
Lakes region and interior Northeast. This system will usher in
showers and thunderstorms to areas with increased soil saturation
and lower FFGs. The broad Marginal Risk was maintained from the
Tennessee Valley to the New Hampshire/Maine border given the
increasing signal for heavier and more widespread QPF.

Campbell
$$
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FOUS30 KWBC 240759
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
359 AM EDT Thu Apr 24 2025

Day 1
Valid 12Z Thu Apr 24 2025 - 12Z Fri Apr 25 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE CENTRAL/SOUTHERN PLAINS AND IOWA...

The latest suite of guidance continues to be be highly variable
with the placement of highest QPF; however persisted with increases
over Iowa as well as Oklahoma and Texas. The Slight Risk saw a
southward expansion for the Hill Country and to the northeast
placing the northern boundary into central Iowa. Meanwhile there
was a reduction across western Oklahoma and along the Missouri and
Kansas border. Areal averages of 1 to 2 inches with local maximums
of 4+ inches possible.

Multiple clusters of thunderstorms will likely be ongoing. With peak
heating and the increased instability there will be renewed rounds
of showers and thunderstorms. Since this is likely to occur over
many of the same areas hit with recent heavy rain this will once
again renew the potential for localized flash flooding over
portions of the Southeast. There will be a steady influx of Gulf
moisture streaming over the stalled boundary which will maintain
support for heavier rainfall with the strongest storms, and greater
coverage of showers and storms in general. A Marginal Risk covers
the northern Gulf states and Southeast.

Campbell


Day 2
Valid 12Z Fri Apr 25 2025 - 12Z Sat Apr 26 2025

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHERN PLAINS, MID-MISSISSIPPI VALLEY, OHIO VALLEY, AND
PORTIONS OF THE NORTHEAST...

A strengthening surface low developing ahead of a strengthening
upper level shortwave trough will drive the storms from a forcing
standpoint through the period. Starting in the Plains it will track
northeast into the Great Lakes Friday evening, with showers and
storms forming along the cold front to the south and east of the
low center. This will bring periodically heavy rainfall to
portions of the Northeast, which has been in a drier period the
past week. Gulf moisture continuing to advect in from the south
will lead to shower and thunderstorm activity starting Friday
afternoon across the Tennessee and Ohio Valleys, and continuing
into Friday night as the front lags behind (south and west) of the
surface low. Meanwhile, the trailing (western) end of the cold
front may be the trigger for additional thunderstorms into southern
Oklahoma, north Texas, and the southern Texas Panhandle.

In coordination will the offices in the Northeast the Marginal Risk
was removed from New Hampshire, Vermont, much of New York and
northeast Pennsylvania. This area has been drier of late and with
green up already in progress, much of the rain will be absorbed
with minimal if any flooding possible. Elsewhere, the Marginal had
minor reshaping to reflect the latest WPC QPF and model trends.

Campbell/Wegman


Day 3
Valid 12Z Sat Apr 26 2025 - 12Z Sun Apr 27 2025

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHERN PLAINS AND FOR PORTIONS OF NEW ENGLAND...

...New England...

Showers and thunderstorms are expected to pass through New England
thanks to upper level shortwave energy and wavy surface fronts.
The flow is expected to be fairly progressive so it will help limit
the potential for flash flood. Given the recent QPF trends and
placement, the inherited Marginal Risk area was significantly
modified to only include northeast Vermont, northern New Hampshire
and the majority of the state of Maine.

...Southern Plains...

The steady influx of rich moisture ahead of a deeply strengthening
storm system ejecting into the Plains will fuel rounds of heavy
rain and thunderstorms across portions of the central U.S. from the
weekend into next week. Guidance has improved its focus on where
the higher QPF will occur. The old Day 4 Marginal Risk was reduced
out of Nebraska and Kansas, now spanning from Texas to western
Arkansas as the new Marginal Risk area for this period. Heavy rain
will be favorable with the upper trough diffluence combined with
front/dryline instabilities.

Campbell

$$
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FOUS30 KWBC 250826
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
426 AM EDT Fri Apr 25 2025

Day 1
Valid 12Z Fri Apr 25 2025 - 12Z Sat Apr 26 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
NORTH TEXAS AND THE TEXAS PANHANDLE INTO SOUTHWEST OKLAHOMA...

...Summary...
Minor adjustments were made to the Slight Risk from yesterday's Day
2 ERO area across western portions of the TX/OK Red River Valley
into the Cap Rock and Rolling Plains. Meanwhile, the Marginal Risk
area farther east was extended to include more of the Lower MS Valley.

...North TX...Central OK...TX-OK Panhandles...Eastern NM
Slight Risk area which was hoisted yesterday in the Day 2 ERO, in
coordination with affected TX/OK offices, continues into today's
Day 1 ERO with minor modifications. Upper level flow gradually becomes
more difluent today and tonight as the upper ridge axis pushes east
across the Southern Plains. Convection early this morning on the
leading edge of the outflow boundary south of the MCS will continue
to diminish south of the Red River, resulting in not much rainfall
from an areal-average standpoint. However, late this afternoon and
into the evening with the daytime heating and more favorable
forcing (increasing difluence aloft), additional storms will
develop along the dryline, likely growing upscale into an MCS that
will track slowly across the TX Panhandle and Red River Valley
into the overnight hours. The activity will parallel a W-E oriented
surface frontal boundary that will become quasi-stationary
overnight. The 00Z high-res guidance again indicated stronger
multicellular clusters and supercells, some of which become slow
moving per the simulated reflectivity guidance. Therefore there is
still concern that stronger storms/supercells within the MCS may
move more slowly or even stall, causing a more enhanced flash
flood risk, while the MCS as a whole remains over an area hard hit
with heavy rain in recent days. Within the Slight Risk area, the
latest (00Z) HREF shows highest probabilities of >5" within 12hrs
(40-50+ percent). Meanwhile, the Slight Risk area is also supported
by the latest UFVS-verified CSU ERO First Guess field.

...Lower-Mid MS Valley and TN Valley to OH Valley and Lower Great
Lakes, Southern-Central Appalachians...
The Marginal Risk inherited from yesterday's Day 2 ERO was expanded
to include more of the Lower MS Valley and a little more of the Mid
Atlantic Region. Over northern areas, deep-layer instability ahead
of the cold front is largely elevated and rather meager (less than
1000 J/Kg). However given the higher relative soil moisture and
lower FFGs over these areas, embedded convective elements may cause
isolated instances of flash flooding.

Farther south across the TN Valley and towards the Gulf Coast,
instability will be more plentiful (Mixed-layer CAPEs of 1000-1500
J/Kg), while TPW values are a bit more favorable as well (between
1.5-1.7"). Despite the more favorable thermodynamic profiles, the
more transient easterly progression of the shortwave energy will
limit the duration of the heaviest rainfall. Still, more elevated
1-2"+/hr probabilities in these areas may lead to localized short-
term runoff issues.

Hurley


Day 2
Valid 12Z Sat Apr 26 2025 - 12Z Sun Apr27 2025

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHERN PLAINS INTO THE SOUTHERN OZARKS AND JUST WEST OF THE
MISSISSIPPI DELTA...

...Southern Plains...
The MCS that is expected to traverse the Texas Panhandle and along
the Red River Valley Friday evening and overnight will persist
into Saturday across the Marginal Risk area. Guidance continues to
show more limited areal coverage of rain on Saturday as compared
with Friday with any additional convection that develops along the
dryline and the quasi-stationary west-to-east front. This
stationary front will eventually lift northeast as a warm front
Saturday night, taking the more organized/widespread convection
with it. Uncertainty regarding MCS behavior on Saturday remains
very high, and further updates and the move of this time frame into
CAMs range may require a later upgrade to a Slight, particularly
if heavy rain remains further west towards the Panhandle for
longer. Regardless, additional convection is likely to form again
Saturday afternoon along the dryline near the New Mexico border,
which may further worsen flooding concerns in the areas where the
storms develop.

Hurley/Wegman


Day 3
Valid 12Z Sun Apr 27 2025 - 12Z Mon Apr 28 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF
THE GREAT BASIN AND FROM PORTIONS OF THE NORTHERN ROCKIES INTO THE
NORTHERN PLAINS AND UPPER MISSISSIPPI VALLEY...

Mid-upper trough across the southern Great Basin early Sunday will
lift across the central Rockies by 12Z Monday. This in-turn will
nudge the upper ridge axis east of the Northern Plains and Upper MS
Valley late Sunday-Sunday night, with a quick onset of upper level
divergence in its wake. Along with the more favorable dynamical
forcing (upper divergence and deep-layer ascent), deepening
southerly flow will tap the western Gulf and lead to an uptick in
low-mid layer moisture transport, with TPW values climbing to
1.25+ inches. Deep-layer instability meanwhile will also be ramping
up, to the tune of 1000-2000+ J/Kg MUCAPE per the 00Z GFS. Some of
the guidance (particularly the ECMWF) shows an MCS developing along
the western periphery of the upper ridge, then tracking east to
eventually southeast along the 850-300 mb thickness. At this point
(day 3 forecast) the forward-propagating Corfidi vectors would
support a more progressive MCS, though much will depend on the
strength of the LLJ. For now, have maintained a fairly broad
Marginal Risk area given the potential of intense short-term
(sub-3hr) rainfall rates.

Hurley

$$
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FOUS30 KWBC 260829
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
429 AM EDT Sat Apr 26 2025

Day 1
Valid 12Z Sat Apr 26 2025 - 12Z Sun Apr 27 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
NORTH AND NORTHWEST TEXAS INTO SOUTHERN OKLAHOMA...

...Summary...
Based on the latest observational and guidance trends, have
expanded the Slight Risk from yesterday's Day 2 ERO a little
farther west-southwest to include a bit more of the Rolling Plains
in Northwest Texas. Otherwise, more minor adjustments were made to
the surrounding Marginal Risk area.

...Southern Plains...
MCS and resultant MCV currently traversing the Texas Panhandle
early this morning will gradually track ENE along the quasi-
stationary surface frontal boundary across much of the TX-OK Red
River Valley today. By late morning, the weakening LLJ will allow
the MCS to diminish, while later in the day (afternoon) a narrow broken
line of convection develops farther upstream along the dryline
across Northwest TX during peak heating. This second area of
convection is expected to take on a more ESE trek during the
afternoon and evening, thus the southwest 'bulge' to both the
Slight and Marginal Risk areas across the Rolling Plains and (for
the Marginal Risk) into northern portions of the Hill Country.
Overnight, the surface stationary front will eventually lift
northeast as a warm front Saturday night, taking the more
organized/widespread convection with it.

As with yesterday's Day 2 ERO, the Day 1 Slight Risk area was
adjusted to capture areas where 1-2+ in/hr rainfall rate probabilities
from the HREF/RRFS ensembles are highest, while also overlapping
areas where heavy rainfall has fallen over the past couple of days
(wetter antecedent interviews).

Hurley


Day 2
Valid 12Z Sun Apr 27 2025 - 12Z Mon Apr 28 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE NORTHERN HIGH PLAINS INTO THE UPPER MISSISSIPPI VALLEY...

Mid-upper trough across the southern Great Basin early Sunday will
lift across the central Rockies by 12Z Monday. This in-turn will
nudge the upper ridge axis east of the Northern Plains and Upper MS
Valley late Sunday-Sunday night, with a quick onset of upper level
divergence in its wake. Along with the more favorable dynamical
forcing (upper divergence and deep-layer ascent), deepening
southerly flow will tap the western Gulf and lead to an uptick in
low-mid layer moisture transport, with TPW values climbing to 1.3+
inches. Deep-layer instability meanwhile will also be ramping up,
to the tune of 1000-2000+ J/Kg MUCAPE per the 00Z models. To some
degree, the latest models indicate MCS development along the
western periphery of the upper ridge, tracking east to eventually
southeast along the 850-300 mb thickness. For the most part, the forward-propagating Corfidi vectors would support a rather
progressive area of any organized convection that can grow
upscale, though much will depend on the strength of the LLJ. For
now, have maintained a fairly broad Marginal Risk area given the
potential of intense short-term (sub-3hr) rainfall rates.

Hurley


Day 3
Valid 12Z Mon Apr 28 2025 - 12Z Tue Apr 29 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE NORTHERN PLAINS INTO THE UPPER MIDWEST...

Mid-level circulation will open into a shortwave trough across the
northern Plains and Upper Midwest on Monday-Monday night. Ample
pre-frontal low-mid layer moisture transport and PW values climbing
to 1.5-1.75" will make for a favorable thermodynamic profile,
along with deep-layer instability as MUCAPEs peak between
2,000-3,000 J/Kg (even ~1,000 J/Kg wrapping westward into the
TROWAL zone). The biggest concern during this period will be with
cell training, especially late Monday-Monday night across the Upper
Midwest with the strengthening LLJ and weakening downwind Corfidi
Vectors. For now, guidance spread with the heavier QPF is still
rather high (not well consolidated to support a Slight Risk at
this point). However, per the GFS/ECMWF and especially the GEM-
Regional, localized totals of 3-5+ inches within 12 hours would
appear likely in this setup.

Hurley

$$
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FOUS30 KWBC 270830
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
430 AM EDT Sun Apr 27 2025

Day 1
Valid 12Z Sun Apr 27 2025 - 12Z Mon Apr 28 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTH-CENTRAL AND SOUTHEASTERN MONTANA...

...Summary...
Minimal modifications were made to the Slight and Marginal Risk
areas from yesterday's Day 2 ERO.

...Northern High Plains to the Mid Mississippi Valley...
Mid-Upper low migrating across the central Great Basin-central
Rockies during the period will set the stage for robust deep-layer
forcing over the outlook areas as the upper ridge axis moves east.
Helping matters will be coupled upper level jet streaks, i.e. with
the ribbon of enhanced lift within the right-entrance region of the
upper jet streak traversing south-central Canada, while also
within the left-exit region of the upper jet streak lifting into
the Front Range and Central Plains. Robust low-mid level moisture
transport turning westward into the maturing Cold Conveyor Belt
(CCB) and maturing TROWAL will reach 2-3 standard deviations above
normal across the Northern Plains per the 00Z GEFS, while
anomalies peak between +3 and +5 across the Upper MS Valley Sunday
night. This as the south-southwesterly LLJ peaks by Sunday night
(~50 kts at 850 mb), while strengthening ENE-NE low-level flow
peaking between 30-40 kts across the backside of the CCB will lead
to a considerable upslope component to the lift across the
foothills and High Plains of south-central and southeast MT into
northeast WY.

The Slight Risk area was largely unchanged. Peak rainfall totals of
2-4+" west and southwest of Billings will combine with high snow
levels and burn scars to locally enhance the flash flooding
potential in this area of Montana. Farther east across the northern
Plains and Upper MS Valley, deep-layer instability will become more
plentiful (MUCAPEs peaking aoa 1,000 J/Kg), while the low-level
moisture transport becomes more robust Sunday night given the
aforementioned uptick in the LLJ. Despite the more favorable deep-
layer thermodynamical profile, the spread in the model QPFs is much
higher over this area, particularly with the heavier rainfall. This
is likely to the more transient (less persistent), mainly WAA-
driven upper level forcing, along with the low-level fronts
remaining upstream of the Upper MS Valley through Sunday night. In
addition, the forward-propagating Corfidi vectors would support a
rather progressive motion of any organized convection that is able
to grow upscale. As a result, the Marginal Risk area was
maintained across the lower (Northern) Plains and Upper MS Valley.

Hurley


Day 2
Valid 12Z Mon Apr 28 2025 - 12Z Tue Apr 29 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE NORTHERN PLAINS INTO THE UPPER MIDWEST...

...Summary...
Based on the favorable deep-layer synoptic forcing and
thermodynamic profile and the uptick in areal-average model QPFs
(especially the upper-bound totals), have hoisted a fairly large
Slight Risk area across parts of the Northern Plains and Upper
Midwest. Also expanded the Marginal Risk area across SD, southwest
MN, and Iowa from yesterday's Day 2 ERO.

Mid-level circulation will open into a shortwave trough across the
northern Plains and Upper Midwest on Monday-Monday night. Ample
pre-frontal low-mid layer moisture transport and PW values climbing
to 1.5-1.75" will make for a favorable thermodynamic profile,
along with deep-layer instability as MUCAPEs peak between
2,000-3,000 J/Kg (even ~1,000 J/Kg wrapping westward into the
TROWAL zone). The biggest concern during this period will be with
cell training, especially late Monday-Monday night across the Upper
Midwest with the strengthening LLJ (50-55 kt at 850 mb) and
weakening downwind Corfidi Vectors. The 00Z guidance has become a
bit more clustered with the heaviest QPF within the Slight Risk
area, with pockets of 3-5+ inches per the higher-resolution models.

Hurley


Day 3
Valid 12Z Tue Apr 29 2025 - 12Z Wed Apr 30 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE SOUTHERN PLAINS INTO THE OZARKS AND LOWER MISSOURI VALLEY...

Another potential significant rainfall event will be taking shape
across western portions of the TX-OK Red River Valley northeast
into the Ozarks and Lower MO River Valley. This as the upper trough
west/ridge east amplify and in-turn exhibit slower W-E
progression. This will allow for a more prolonged period of
favorable upper level forcing (coupled southern and northern stream
jet streaks) along a surface front that will become quasi-
stationary across OK- southeast KS into central MO. Robust
synoptic-scale forcing, favorable thermodynamic profiles (Mixed
Layer CAPEs 1000-2000 J/Kg and TPWs 1.5-1.75") and the the enhanced
risk of repetitive convection along the slow moving/stalled
frontal boundary will likely lead to impressive 24 hr rainfall
totals within the Slight Risk area (3-5+ inches, with higher
localized totals per the higher-resolution GEM-Region and RRFS
runs). Tuesday night in particular may bring a more enhanced flash
flood threat, as the LLJ veers and becomes nearly parallel (and of
similar magnitude of) the mean 850-300 mb flow, thereby leading to
weaker forward-propagating Corfidi Vectors and allowing for a
greater risk of cell training.

Hurley
$$
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FOUS30 KWBC 280742
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
342 AM EDT Mon Apr 28 2025

Day 1
Valid 12Z Mon Apr 28 2025 - 12Z Tue Apr 29 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE PLAINS AND INTO THE UPPER MIDWEST...

...Northern Plains & Upper Midwest...

The period in question will remain active on the rainfall front, but
a few key pieces will be missing, relegating flash flood prospects
closer to the MRGL risk category as inherited from the previous
update. Upper level progression from the Inter-Mountain West through
the Northern Plains and Upper Midwest will exhibit a decaying mid to
upper level structure of a closed ULL out west with a more sheared,
progressive pieces ejecting into the High Plains and propagating
northeastward through MN and northern WI. The evolution is such that
a reasonable upper forcing pattern will materialize with scattered
to widespread convective initiation located downstream of a broad
diffluent axis situated from the Front Range through the Upper
Midwest. Instability on the order of 1500-2500 J/kg of MUCAPE will
be present ahead of the mean trough with ample mid-level
perturbations ejecting into the northern tier of the CONUS during
the morning and afternoon periods. To round off the setup, a budding
140-150kt jet streak will be oriented over south-central Canada
providing a solid RER dynamic suitable for maintaining a more
organized precipitation element over the northern tier of the CONUS.
Despite the above support for convective prospects, the pattern will
be in the process of breaking down as the upper low out west becomes
a more open wave with the primary bulk of mid-level energy quickly
ejecting northeast with a textbook strong PVA to NVA signature as
the energy vacates over the northern Lakes. This setup has shifted
to a very front loaded convective scheme over the Northern Plains
into the Upper Midwest with a majority of the convective pattern
quickly ushering east-northeastward through the course of the
morning and afternoon periods. By the evening, remnant convective
elements will become more scattered in nature, eventually moving out
of the primary area of interest after nightfall leading to a
diminished threat for the end of the forecast cycle.

00z HREF EAS probs remain pretty elevated (50-80%) for at least 1"
across the eastern half of ND through Northern MN, but a sharp
decline in probs for >2" leading the case for more isolated to
widely scattered flash flood prospects in the given pattern. There
are some respectable probabilities in the neighborhood scheme for

2" within the Arrowhead of MN back over the the Dakotas (50-80%),

but again a sharp decline once into the >3" fields limiting the
upper bounds of the potential. A few areas may see between 3-5" at
the peak, but those will likely be few and far between for an area
that is actually in a low-end drought overall. Considering the soil
type and antecedent dry conditions in the region, the inherited MRGL
was maintained with little change in the risk area over the Northern
Plains into the Upper Midwest.

...Central and Southern Plains...

The Central and Southern Plains will reside within a broad warm-
sector environment positioned between a vacated warm front pressing
north through the Mississippi Valley and a slow-moving cold front
through the High Plains with a secondary cold forecast to plunge
southeast through the Northern and Central High Plains by the end of
the forecast cycle. A fairly meridional upper pattern will end up
being a key factor in the eventual ejection of stronger shortwaves
out of Chihuahua, MX, barreling northeastward through the Southern
Plains with scattered to widespread thunderstorm development along
and east of a dry line situated over West TX. The combination of
relevant buoyancy/instability positioned over the Southern and
Central U.S. coupled with favored regional ascent and
thermodynamics will create a period of late-afternoon and evening
convective development capable of localized flash flood prospects.
Recent heavy rain episodes have contributed to an elevated soil
moisture presence from the Red River Basin up through much of OK
into southeast KS, and MO. Rainfall totals up to 2-3" in a short
time frame will be capable of causing flash flooding within the
bounds of those areas that exhibit those moist top-layer soils
since the time frame for recovery will have been short. 00z HREF
neighborhood probs for >1" are respectable (50-70%) within portions
of the Central and Southern Plains with the focus generally over
north-central OK, Concho Valley, and Western Rolling Plains of West
TX. Probabilities for >2" are very low leaving the threat for
flash flooding fairly conditional and likely more reserved for more
sensitive areas within urbanized zones and areas more susceptible
due to low-water crossings.

Kleebauer


Day 2
Valid 12Z Tue Apr 29 2025 - 12Z Wed Apr 30 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHERN PLAINS INTO THE MISSOURI VALLEY...

The combination of favorable buoyancy and upper level dynamics
within the confines of a quasi-stationary front across the Southern
Plains to Mid-Mississippi Valley will create an environment
conducive for locally heavy rainfall over an area still recovering
from previous heavy rain episodes. Models are in agreement on the
placement of a west-southwest to east-northeast oriented stationary
front extending from the Western Rolling Plains of TX up through the
Red River Basin, bisecting much of central and northeastern OK, up
through the Ozarks of MO. Multiple mid-level shortwaves will eject
northeast out of MX creating a multi-wave convective initiation
cycle that will eventually move over the same areas repeatedly
during the course of the D2 time frame. Instability markers are very
favorable within the axis denoted above with sufficient buoyancy
on the order of 1500-3000 J/kg of MLCAPE situated across West TX to
points northeast through the Red River into OK. Assessment of NASA
SPoRT soil moisture anomalies pinpoint a fairly large area of
well- saturated top-layer soils running upwards of 90-98th
percentile across southwestern OK up into the Norman/OKC metro
corridor thanks to a significant flash flood episode that occurred
less than 36 hrs prior. Further northeast, soils are still
recovering from multiple rounds of convection the past several days
with elevated top-layer soils also running high within the 75-90th
percentile across the Tulsa CWA up through southwestern MO.
Considering guidance privy to these areas also being the
beneficiary of multiple convective rounds over the course of
Tuesday into Wednesday, there is a growing necessity for a higher
risk level forecast in these zones. Ensemble bias corrected
guidance has steadily increased the areal QPF averages from run to
run within these confines of northeast OK up through western MO, a
testament to the growing consensus in the heavy QPF footprint.

00z CAMs are only within the initial 12 hrs. of the period in
question, but the signs even prior to the bulk of the heavier
convective signature (Heaviest after 00z/29) are very much favorable
for potentially significant flash flood prospects. 00z HREF 6-hr FFG
exceedance probabilities for the 18-00z time frame are already
between 15-30% on the initial stages of heavier precip across the
Red River Basin of North TX into Southwestern OK up through Central
and Northeast OK. This is very likely due to the convective episode
stemming from the first mid-level shortwave ejecting northeast
generating a period of convection during the afternoon hrs. on
Tuesday. By Tuesday evening, large scale ascent will increase
substantially over the Southern Plains a potent mid-level shortwave
pivots over NM with a robust diffluent signature present downstream
into West TX and the adjacent Red River Basin. At the surface, a
cold front will motion south through the High Plains with an
expected convergence pattern developing as it moves into the already
present quasi-stationary front in place across the region. The
combination of the evolving surface and upper pattern will yield a
robust convective footprint across the Southern High Plains of TX up
through the Red River Basin, pressing northeast given the steering
pattern aloft. The episodic nature of the heavy precip will garner
limited recovery for areas already impacted by one round of
thunderstorms earlier in the period leaving a better opportunity for
flash flooding potential for the nocturnal period. There's some
discrepancy on exact placement of the more prolific convective
cores, but the one constant is the area expected to see the threat
is generally pinned down at this lead.

After coordination with local WFOs over North TX through OK,
Southeast KS, and Southwest MO...the previous MDT risk was expanded
to include much of Central and Northeast OK up through Southeast KS
into Southwest MO. A large SLGT encompasses areas surrounding the
MDT risk with areas like the eastern Permian Basin, Concho Valley,
and the Southern half of MO (Excluding the MDT risk area) within the
SLGT corridor. A broad MRGL extends from the rest of the Permian
Basin all the way through the Central and Northern Ohio Valley into
Northwest PA and far Southwest NY state as scattered convective
clusters will have the opportunity in these zones to produce locally
heavy rainfall capable of isolated flash flood prospects.

Kleebauer

$$
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FOUS30 KWBC 290739
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
339 AM EDT Tue Apr 29 2025

Day 1
Valid 12Z Tue Apr 29 2025 - 12Z Wed Apr 30 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
SOUTHERN PLAINS...

...Southern Plains...

A repetitive scheme of successive convective outputs across
portions of West TX through Oklahoma will result in significant
flash flooding for a large portion of the above areas. The
combination of several mid-level impulses ejecting northeast within
a large scale diffluent pattern will interact with a quasi-
stationary front aligned from the Western Rolling Plains of TX up
towards the Red River Basin mainly west of I-35. Favorable mid-
level ascent will allow for waves of convective initiation
beginning late-morning and afternoon Tuesday with a secondary pulse
around 00z Wednesday with a final pulse forecast after 06z as the
mean trough finally starts pivoting east out of the Southwestern
CONUS. Instability within the confines of West TX up to the Red
River will allow for rapid development of convective clusters with
some supercellular modes plausible prior to nightfall, eventually
merging into a more multi-cellular scheme with backbuilding favored
within the confines of the front denoted pretty well within the
theta_E gradient output in each deterministic. All CAMs are well
supportive of the 3-wave convective evolution with heavy rainfall
situated across the Southern High Plains near the eastern Permian
Basin with a general QPF maxima aligned southwest to northeast
across the northern extension of the Rolling Plains in TX, up
through the Red River and into the southern portion of the OKC
Metro. This area has been the benefactor of multiple convective
episodes already, leading to flash flooding within the corridor
extending from Lawton down to the Red River. This area will be the
most primed location for not only widespread flash flooding, but
significant life-threatening flash flood prospects due to the well
above normal soil moisture anomalies likely curbing any potential
for rainfall to soak into the top soil layer.

Latest 00z HREF probability fields are overwhelmingly indicative of
the threat with one of the more robust indications occurring
within the 6-hr FFG exceedance probability marker running between
70-90% across the area extending from Foard County in TX up to
western Cleveland County in OK. Neighborhood probabilities of >5"
total rainfall are running between 50-80% in the same location with

8" between 20-30% across Southwest OK between Lawton to the Red

River. Neighborhood probs for >3" are significant across much of OK
back into North TX with the southwest extension back into the
southeast corner of the LUB CWA. Considering the NASA SPoRT soil
moisture percentiles running between 70-99% for the 0-40cm layer
across the entire area above, the propensity for flooding, even in
rural zones will be higher than normal. Given expected rates
between 1-2"/hr during peak storm cycles and the expectation for

3" of rainfall...the threat will be of the higher magnitude in

terms of impact prospects. The previous MDT risk inherited was not
only maintained, but expanded a bit further southwest to align with
the higher probabilities with the neighborhood >5" potential and
the elevated HREF EAS >2" probabilities that have been depicted. A
high-end MDT risk is forecast across the Red River Basin west of
Wichita Falls up into the southern fringes of the OKC metro,
including the town of Norman. Lower end probabilities for flash
flooding will exist across areas of the eastern Permian Basin out
through the Concho Valley as well as across much of Oklahoma not
included in the MDT.

...Mississippi and Ohio Valleys...

Mid-level impulses that eject out of the Southern Plains will
continue to press northeast towards the Mississippi and Ohio
Valleys with a progressive cold front moving southeast out of the
Midwest during the same time frame. Afternoon destabilization
coupled with the favorable addition of mid-level forcing and surface frontogenesis will lead to scattered convective pulses across the
region with some organized elements focused within the confines of
the front and under the shortwave propagation. Soils remain moist
across much of the region extending from MO through the Ohio River
Basin with an eastern extension to the Central Appalachians and
Western PA Highlands. PWAT anomalies on the order of +1 to as high
as +2.5 deviations cements a favorable deep moist environment
conducive for heavy rainfall prospects within any convective
scheme. The greatest concentration of heavy rain will likely be
back over Southern and Central MO towards the 3 river confluence
zone near KY/MO/IN/IL. HREF probs for >1" are very high (70-90+%)
across much of the Mississippi and Ohio Valley areas with >2" probs
relatively high (50-70%) in-of the Ohio River Basin over Southern
IL through much of Eastern KY. The combination of convection over
areas that are still in recovery from previous rainfall episodes
and complex terrain will create a threat for isolated to perhaps
scattered flash flood instances over a large area during the
afternoon and evening hours Tuesday. A SLGT risk remains firmly in
place across much of MO along and south of I-70 until the 3 river
confluence zone referenced above. A MRGL risk encompasses all other
areas east through Western PA and even the southwest corner of NY state.

Kleebauer


Day 2
Valid 12Z Wed Apr 30 2025 - 12Z Thu May 01 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE ARKLATEX, EASTERN OKLAHOMA, AND WESTERN OZARKS...

The pattern remains very active as we move into Wednesday as the
mean trough slowly slips eastward with ample mid-level energy
accompanying, creating an environment favorable for organized
convective clusters through the entire D2 time frame. Rich Gulf air
will be pulled poleward ahead of the advancing trough with several
mid-level perturbations ejecting out of the ahead of the primary
shortwave trough. This in combination with sufficient buoyancy
across Central and East TX through the Mississippi Valley will
maintain a widespread convective zone of impact with strong, heavy
thunderstorm cores and clusters capable of producing prolific
rainfall totals.

Two primary periods of interest have become fairly well documented
within the recent deterministic cycles. The first is the
continuation of the convective complex that will develop overnight
Tuesday into Wednesday morning over the western Red River Basin and
slowly trudge eastward as it maneuvers in tandem with the primary
shortwave energy, and across the remaining theta_E gradient running
parallel to the river. 00z HREF on the back end of its run is
signaling some very impressive rainfall totals (2-5") within the
first 12 hr. period in the forecast cycle (12z Wed to 00z Thu)
across places along the Red River up through Central and Eastern OK
as the multi-cell cluster advances. Prob fields for >3" within
that first 12 hrs. are between 50-90% across south-central OK,
along and east of the I-35 corridor with 25-40% probs for even >5".
Considering this is only for the first 12 hrs., the probs are
pretty impressive and really highlight the threat on the initial
heavy QPF core.

The second period of interest will occur in the afternoon and
evening hrs. as diurnally driven convection will flare up over
Eastern TX within a broad moisture rich environment as NAEFS
anomalies continue to point to +2 to +3 deviations for PWATs
(1.5-2") situated over the area. LLJ introduction by early evening
will only exacerbate the potential with increasing low-level shear
capable of persisting updrafts and eventual cell clusters that will
originate from cells moving northeast within the mean flow. Several
mid-level perturbations will be in the vicinity across Northeast TX
to truly enhance and maintain convective cores such that it becomes
a fairly favorable prospect for heavy rainfall extending into the
Lower Mississippi Valley. Totals between 2-4" within an areal
expanse are forecast across the ArkLaTex up through Western AR to
just before the MO Ozarks. Locally higher totals will be possible
across that entire area given the favorable rates between 1-2.5"/hr
forecast currently within global deterministic. Pending outflow
propagation within the setup, heavier totals could advance further
east towards Central AR, but at this juncture, the primary area of
focus aligns over East TX up through Eastern OK and Western AR.
This correlates well with the theta_E ridge extension up through
the area where convective threats will be highest during peak
diurnal destabilization and beyond.

The previous MDT risk was maintained with a westward extension back
over portions of south-central OK down across the Red River into
TX. The MDT risk is NOT within the DFW metro, however it does lie
just north, so will have to monitor trends closely over the next
24-36 hrs. A broad SLGT risk extends south into East TX but well
north of the TX Gulf Coast.

Kleebauer
$$
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FOUS30 KWBC 300733
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
333 AM EDT Wed Apr 30 2025

Day 1
Valid 12Z Wed Apr 30 2025 - 12Z Thu May 01 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTH-CENTRAL AND SOUTHEAST OKLAHOMA, NORTH TEXAS, AND WESTERN ARKANSAS...

The overall synoptic pattern remains unchanged in terms of the
general longwave progression as an amplified mid-level trough
begins to open up overnight and kick eastward with a strong
vorticity maxima riding the base of the mean trough. Ample mid-
level ascent within a fairly moisture rich environment thanks to
coupled LLJ advection and strong 700-500mb moisture feed from the
above trough will lead to a period of prolonged convective
maintenance and initiation over the course of Wednesday into early
Thursday morning. A strong mid-level shortwave ejection is
currently migrating eastward out of NM with WV and IR satellite
already showing instances of cooling cloud tops marking the sign of
the final wave of convective initiation off the Caprock and
adjacent Permian Basin. This expanse of convective development will
usher east-northeastward within the mean flow, also anchoring to
the quasi-stationary boundary positioned back across the Permian
Basin through the Western Rolling Plains of TX. Heavy thunderstorms
prior have led to a swath of very low FFG's in their wake creating
an antecedent soil moisture condition incapable of taking on much
more rainfall before causing flash flooding, some significant in
nature given the ongoing issues near the Red River.

As the shortwave trough migrates through North TX and the Red River
Basin, cold pool convergence during nocturnal convective cycles
will lead to a conglomeration of heavy thunderstorms extending from
Central OK down through North TX, advancing eastward within the
confines of the stationary front. By 12z Wednesday, rainfall rates
between 1-2"/hr at peak intensity will encompass a pretty large
area with the western extent of the precip footprint likely
overlapping areas that were hit recently this evening. This area
will represent the western extent of the inherited MDT risk as
outlined as 00z CAMs have come into relative agreement on the
timing of the convective cluster moving through the region in the
initial stages of the forecast cycle. The primary energy will
continue to traverse eastward with the afternoon period likely to
see the shortwave axis bisecting Southeast OK between the 18-00z
time frame. This is where the next round of convective impacts will
transpire.

As of the latest ensemble bias corrected mean and HREF blended mean
output, the heaviest precip has shaded a bit further south compared
to run-to-run consistency, a tendency typically seen in these
setups due to the greater instability located further south, as
well as cold pool progression tending to move southeastward within
the theta_E gradient pattern(s). This is no different with a strong
signal for 2-4" areal averages located over Northeast TX with the
2" mean now even southeast of the DFW metro. 3-5" is the average
over the ArkLaTex bisecting the Red River Basin between OK/TX/LA,
something that has remained steady despite the overall shift
further south in the heavier convective forecast. This is the most
likely location for flash flood prospects, certifying the centroid
of the current MDT well-positioned and left untouched from previous forecast.

With the scope of the heavier precip now aligned a bit further
south to include the DFW metro and areas along I-20, the MDT was
pulled a bit further south to encompass the 00z HREF >5" neighborhood
probs of at least 30% or higher, with the general maxima located
along I-30 towards Texarkana. This correlates well with the
forecasted position of favorable PWAT anomalies +2 or better when
assessing the most recent NAEFS and ECENS outputs. Hourly rates
between 1-2"/hr will be most common at peak intensity according to
the HREF hourly prob fields with 1"/hr running between 50-90% at
any given time between 18-06z in the forecast across Northeast TX
up into Southeast OK and Western AR. 2"/hr probs are not as
prolific in the signal, but considering the sheared profile and
deep boundary layer moisture advection pattern, would not be
surprised to see some cells percolate >2"/hr given the expected environment.

The DFW metro is one of the areas of focus due to the risk of flash
flooding being higher with the urbanization factors at hand. There
are some CAMs hinting at significant totals within the metro
proper, but some are just missing the population center to the
north and east during the overall evolution. Considering the
environmental conditioning and the nature of the heavy precip being
within a short proxy, regardless of eventual outcome the MDT risk
was sufficient to cover for the threat. HREF EAS prob fields for at
least 2" running between 30-50%, west to east across the metroplex
is a pretty good signal for the threat and that signal only
improves as you move eastward through the I-20/30 zones.

There is a large SLGT risk that encompasses much of the Lower
Mississippi Valley and basically the rest of the northeastern
quadrant of TX up through Central OK. Scattered to bordering
widespread convection will be forecast from the Ozarks and points
southwest with some locally enhanced cores likely to spur some
flash flood potential with low to medium grade probabilities
suggest. There's some question on the exact location of these more
isolated heavy cells, however there's some indication a secondary
maxima could be within south-central TX near the eastern flank of
the terrain east of I-35, or across MO where diffluent upper flow
will be positioned well to enhance regional convective coverage
within a fairly moist environment as the anomalous PWATs funnel poleward.

Kleebauer


Day 2
Valid 12Z Thu May 01 2025 - 12Z Fri May 02 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER A BROAD
AREA FROM THE GREAT LAKES TO MID MISSISSIPPI VALLEY TO WESTERN GULF COAST...

Surface cyclogenesis across the Southern Plains will lead to a
steady low progression to the northeast up through the Mississippi
Valley into the Great Lakes towards the end of the forecast cycle.
A cold front will trail the vacating low allowing for some frontal
convergence to occur across the above areas with the greatest
convective coverage likely to be within the warm sector of the Ohio
and Tennessee Valley into the southern Great Lakes. PWAT anomalies
between +2 and +3 deviations will be present for much of the CONUS
situated east of the Mississippi lending to a fairly rich
environment conducive for moist convective cores from the Gulf
coast up to the Great Lakes region. The reasoning for the heavier
convective threat north is the added sheared profiles within the
bounds of the warm sector creating better mesocyclone maturity and
stronger storms. All this to say....heavy rain prospects for longer
periods more likely within the zone encompassing the Tennessee and
Ohio Valleys. Current forecast totals region-wide over the
Southeast up into the Ohio Valley are pretty consistent with an
areal average between 0.5 to 1" with some locally enhanced totals
reaching upwards of 2-2.5" in the hardest hit locations. Given
rainfall rates peaking between 1-1.5"/hr when assessing the
probabilistic output of both the NBM and 00z HREF, there's a cap on
the higher end potential of any flash flood scenario leaving this
overall threat in the broad MRGL risk coverage, as inherited.

There is another area of interest down across the Rio Grande
extending from the Big Bend down to about Laredo for tomorrow
evening as a shortwave perturbation ejects east off of Coahuila
with some convection spawning over the Serranias del Burro. Some of
the CAMs are pretty significant in the overall convective
development, but much of the CAMs reach the end of their runs prior
to the activity making its way towards the Rio Grande Valley. Other deterministic and ensemble bias corrected means tell the story in
full with some respectable QPF outputs within the above bounds
leading to potentially some localized flooding within some of the
urbanized zones between Del Rio down to Laredo. Considering the
environment to be favorable and this scenario having a long history
of potential, opted to keep the MRGL risk from previous forecast
issuance to outline the threat for a quick 1-3" of rainfall with
locally higher amounts plausible pending cold pool convergence evolutions.

Kleebauer


Day 3
Valid 12Z Fri May 02 2025 - 12Z Sat May 03 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS MUCH OF
CENTRAL TEXAS...

A cold front progression stemming from a trailing cold front and
pressing surface high over the Northern Plains will lead to
significant low-level convergence regime over Central TX by Friday
afternoon. Return flow around the western flank of a broad surface
ridge positioned over the Western Atlantic will reach back towards
the southern half of TX leading to a convergent pattern in
conjunction with slow-moving cold front moving north to south.
Models have been steadily increasing precip coverage within the
confines of the boundary once it makes headway into the Hill
Country of the Lone Star State by late-Friday morning, carrying
through the rest of the period as the front encounters higher
theta_E airmass within the western periphery of that surface ridge.
PWATs between +1 and +2 deviations will be present once the front
makes its presence across the region, a sufficient environment for
deep moist convective development along and ahead of the boundary
as it slowly migrates south. Ensemble means have upped precip
output in recent runs with a solid 1-2" areal average now
encompassing a large portion of the state from the Stockton
Plateau, east through Hill Country, the I-35 corridor, all the way
back towards the Piney Woods area of East TX. Favorable environment
with likely training echoes in proxy to the cold front will
generate locally enhanced QPF maxima, especially within the bounds
of the terrain where an added weak upslope component could yield
greatest results (3+" totals). The convergent pattern can be seen
as far east as the Southeastern CONUS, but the greatest surface
frontogenesis signal is situated back over the Southern Plains,
south of I-20.

A SLGT risk was added across the above area with a broad MRGL
encompassing the higher risk as scattered convection will still be
present up towards I-20 extending east through the Lower
Mississippi Valley up through Northern AL and Eastern TN. Will be
monitoring the setup closely as the setup will likely be most
prolific within one of the flashier areas of the country.

Kleebauer
$$
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FOUS30 KWBC 010756
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
356 AM EDT Thu May 1 2025

Day 1
Valid 12Z Thu May 01 2025 - 12Z Fri May 02 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN SOUTHERN
OKLAHOMA, FAR NORTH TEXAS, FAR WESTERN ARKANSAS, WESTERN
PENNSYLVANIA AND THE CENTRAL APPALACHIANS...

...Southern Plains...

Shortwave ejection out of the Southern Rockies will interact with a
cold front pressing south through the Central and Southern Plains
by the late-afternoon and evening hours Thursday through Friday
morning. A relevant theta_E differential will be aligned within
the confines of the boundary providing a suitable thermodynamic
alignment such that area convection anchors and pushes along the
west to east oriented instability gradient across Southern OK.
Majority of CAMs are in consensus of a heavy rainfall footprint
along and south of I-40, generally configured to the timing of the
cold front, shortwave interaction, and LLJ convergence signal. This
is primarily right around 00z when the convective threat enhances
with the integration of the nocturnal LLJ, a timing historically
prevalent for this time of year and this setup is no exception.

00z HREF neighborhood probs for >1" are relatively high (50-80%)
within the corridor extending from Southwest OK across the Red
River Basin towards the AR border. >2" is highest just north of the
river from I-35 on east, a testament to the timing of the
shortwave arrival and upscale growth of the convective threat as it
maneuvers to the east-southeast. Rainfall rates between 1-2"/hr are
most likely when assessing the hourly rate probs from the both the
NBM and HREF output, a rate assessment that is more than suitable
considering the blanket low FFG intervals due to the antecedent
moist soils from the past 36-48 hrs of rainfall. The areal QPF
footprint of >1" aligned within those lower FFG's pretty much
perfectly, a scenario that lends to a greater credence of a touch
higher risk category that what is normal the case for this setup.
The previous SLGT risk was relatively maintained with minor
adjustments on the edges pertaining to recent hi-res QPF and in
conjunction with the ML First Guess Fields.

...Interior Mid Atlantic...

Shortwave trough currently positioned over the Southern Plains will
lift northeast through the Mississippi Valley with sights on the
Great Lakes region by the second half of the D1. Downstream, an
improved diffluent signature will align over the Ohio Valley and
points northeast allowing for regional ascent to boost convective
initiation in-of places within that diffluent core. The most
notable area for convective development lies within an established
theta_E tongue riding northward through the Appalachians Front
with poleward expansion into the southeastern Great Lakes. This
allowed for moisture rich air exuding PWAT anomalies between +2 and
+3 within the corridor extending through much of WV up through
Eastern OH and Western PA to the Lake Erie border. SBCAPE between
1500-2500 J/kg will be a common occurrence during peak diurnal
destabilization creating a corridor of enhanced thermodynamic
prospects to coincide with the arrival of the better mid-level
forcing downstream of the approaching trough. Regional shear will
be improving as well, especially within the confines of a shallow
warm front that will be lifting northward through the course of the
afternoon across the interior Mid Atlantic. Cell initiation will
begin between 18-00z today with greater multi-cell cluster coverage
likely to occur towards the back end of the above time frame due
to anchoring along the warm front as it approaches. Areas across
Western PA have been hit relatively hard recently with convective
rainfall adding to the areal decoupling of the FFG indices meaning
the prospects for flash flooding have increased with the arrival of
this next disturbance.

00z HREF neighborhood probs for >2" are between 30-50% across a
large section of Western PA extending south into the northern High
Country of WV, rooted in the Appalachians Front, an area notorious
for flashy rivers and smaller towns located within the valleys.
There was enough consensus to warrant an upgrade considering the
antecedent conditions, atmospheric environmental favorability, as
well as the increased probs denoting a locally heavy rain prospect
over the region. A SLGT risk has been added to much of Western PA
down into portions of the Central Appalachians.

Kleebauer


Day 2
Valid 12Z Fri May 02 2025 - 12Z Sat May 03 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS FROM THE
SOUTHERN PLAINS INTO THE LOWER MISSISSIPPI VALLEY...

Steady progression of a cold front through the Southern Plains will
lead to textbook convergent pattern with an addition of a strong
upper diffluence signature within the bounds of the southern jet
proxy. High areal theta_E averages will denote the significant
instability pattern positioned ahead of the approaching cold front
leading to ample thermodynamic assistance for strong convective
cores and expected heavy rainfall. Recent CAMs have finally come
into view for the primary window of cell initiation with a
widespread convective pattern likely to extend from the Stockton
Plateau to points east within the I-10 corridor up through all of
Hill Country, especially over the I-35 section of south-central TX.
HREF blended mean QPF is over 2" now within a large area
encompassing the terrain focused across the Central portion of the
state. This had led to elevated neighborhood probs of >2" for the
12-00z time frame in the forecast running >70% over pretty much all
of the above region extending into portions of East TX. The East TX
corridor has become a newer development in terms of anticipated QPF
magnitude as the the CAMs and in some instances the global
deterministic are now catching on to the deep moisture advection
regime poking north out of the Western Gulf ahead of the front
arrival. Forecast soundings across the area between Houston up to
the latitude of Austin are now indicating MUCAPE or the order of
3500-5000 J/kg prior to any front arrival leading to significant
heavy cores to transpire due to cap breach from diurnal
destabilization initially, followed by more organized multi-cell
clusters as we move into the evening as the LLJ re-intensifies and
the cold front motions into the region.

Soundings also note a period of mean flow and upshear components
that would lead to potential backbuilding within the confines of
the front. Very strong ascent between 850-300mb is also noted
within multiple CAMs outputs, a testament to the favorability for
the setup to become more organized and providing a vast areal
expanse of heavy convection once the setup matures. PWATs between
1.6-1.9" with locally >2" are being forecast along and ahead of the
front as it moves into Central TX, a forecast that traditionally is
favored for greater flash flood prospects, especially over the
favored I-35 corridor between Austin to San Antonio where high
runoff capabilities are found due to soil type and limestone
foundations. Local totals between 3-6" are likely over the entire
stretch of Hill Country through East TX with the eastern most
extent even shifting into Western LA as the convective pattern
evolves and grows upscale entering into the adjacent Lower
Mississippi Valley. Houston metro is now in play for convective
impacts, especially as thunderstorms to the north provide outflow
generation that could send cold pools south towards the Gulf coast
with additional convective development along the edge of any
approaching cold pool.

The previous SLGT risk was relatively unchanged across Central TX.
Some expansion to the west was made into the Stockton Plateau where
initial cell formations will likely occur as the front arrives and
interacts with a formidable instability axis aligned over the
plateau itself. The SLGT was expanded southeast to cover the
Houston metro and points north where there is growing consensus on
convective impacts over and near the urban center. This is a high-
end SLGT over much of Central TX, especially Hill Country to the
I-35 corridor and points east. A risk upgrade is not out of the
question in subsequent updates given the environmental
favorability and flashy history of places expected to see the
greatest thunderstorm coverage/rates.

Kleebauer

$$
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FOUS30 KWBC 020825
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
425 AM EDT Fri May 2 2025

Day 1
Valid 12Z Fri May 02 2025 - 12Z Sat May 03 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHERN PLAINS AND MID-SOUTH AND LOWER MISSISSIPPI...

Another round of thunderstorms is expected to develop along and
ahead of a southward moving cold front on Friday...with guidance
still focusing the greatest chances for excessive rainfall from
portions of the Mid-South into the Southern Plains Friday into
Friday night as weak waves propagate northeastward along the front.
Southerly low level flow will draw Gulf moisture northward...helping
increase precipitable water values ahead of the front to 1.5 to
1.75 inches at the time of the peak heating in a stripe from Texas
into southern Arkansas. Forecast soundings depict an atmosphere
supportive of rainfall rates exceeding 2 inches per hour. As
mentioned previously...the potential for a prolonged period of
training is fairly minimal so a Slight Risk still seems to cover
the potential. 00Z HREF neighborhood probabilities of 1-hour QPF
exceeding 2 inches were over 30 percent in parts of southeast TX
with lower probabilities extending into parts of Arkansas.

A Marginal Risk area surrounding the Slight Risk area extends as
far northeastward as parts of the Great Lakes. Precipitable water
values were generally at or below 1.25 inches ahead of the
advancing cold front but guidance still showed enough instability
to support showers and thunderstorms over an area that was still
had lingering hydrologic sensitivity following recent heavy
rainfall. In addition...the area will be underneath a right
entrance region of an upper level jet stream aiding upper level
support during the afternoon.

Farther west...there is also a Marginal risk of excessive rainfall
from late day and evening convection over the terrain of New
Mexico. The QPF is fairly modest but even modest rainfall rates
could result in isolated problems with run off...especially if the
rain falls on recent burn scars.

Bann

Day 2
Valid 12Z Sat May 03 2025 - 12Z Sun May 04 2025

....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM THE GULF
COAST REGION INTO PARTS OF THE EASTERN GREAT LAKES...

The focus for excessive rainfall will shift eastward as a closed
mid-level circulation center takes shape over the nation's mid-
section. The mid- and upper-level flow backs with time from the
Gulf coast northward across parts of the Tennessee and Ohio
Valleys. Initially...this allows deeper moisture to stream
northward. But it also results in the surface/low level front to
move eastward more quickly later in the period...with generally a
low-end risk of flooding from the Gulf coast northward. The 02/00Z
suite of numerical guidance hint that there could be some 1 inch to
perhaps 2 inch amounts where frontogenetic forcing aligns
favorably in between the Gulf and the Ohio Valley...but the signal
for excessive rainfall showed little run to run / model to model
consistency.

There is also a Marginal Risk of excessive rainfall over far
southern portion of Texas...where the southern end of the cold has
stalled its southward progression and return flow of Gulf moisture
has begun. Several of the High Res ensemble highlight this area
with QPF in the upper percentiles although the consensus is less
than unanimous in amounts or placement. With soundings showing
warm cloud processes through a deep layer and the CAPE profile is
tall and skinny...introduced a Marginal risk here.

Bann

Day 3
Valid 12Z Sun May 04 2025 - 12Z Mon May 05 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PARTS OF THE
EASTERN UNITED STATES AND SOUTHERN ROCKIES ...

The risk of excessive rainfall persists across parts of the Mid-
Atlantic and Southeast US as a broad upper trough continues to make
its way eastward on Day 3. Deepest moisture of 1.25 to 1.5 inches
will be eventually be shunted off-shore late in the period. Until then...isolated downpours are possible with spaghetti plots of
2 and 3-inches of rain in 24 hours mainly being produced by models
with the ARW core...but enough members from the NMM core and from
the GEFS to warrant a Marginal.

There is also a Marginal Risk area over parts of New Mexico again
as moisture continue to spread northward and westward from the
Gulf. After 00Z...the flow aloft between the westerly subtropical
jet and a jet streak and low- and mid-levels become increasingly
diffluent with height falls beginning ahead of an approaching
closed low from the west. This...along with moisture and a low
level boundary already in place...should support late day and
evening storms that may produce locally heavy rainfall rates.

Bann

$$
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FOUS30 KWBC 030828
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
428 AM EDT Sat May 3 2025

Day 1
Valid 12Z Sat May 03 2025 - 12Z Sun May 04 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM THE GULF
COAST REGION INTO PARTS OF THE NORTHEAST AND THE SACRAMENTO
MOUNTAINS OF NEW MEXICO

A slow moving mid- and upper-level circulation is expected to form
later today within a broader mid/upper level trough digging
eastward. With low level flow drawing deeper moisture northward
ahead of the system...thunderstorms that form along and immediately
east of a surface cold front will be moving into an environment of
supporting locally heavy rainfall rates and amounts over portions
of the Ohio Valley southward towards the Gulf coast today and from
portions of southern New England southward towards the Carolinas
and areas in and near the southern Appalachians where deeper
moisture resides this afternoon and evening, The 03/00Z suite of
numerical guidance hint that there could be some 1 inch to perhaps
2 inch amounts where frontogenetic forcing aligns favorably in
between the Gulf and the Ohio Valley...but the signal for excessive
rainfall appeared tempered by the progressive nature of the
forcing and confidence was limited by the lack of run to run /
model to model consistency with placement of highest model QPF.

Maintained the previously issued Marginal Risk area in New Mexico
given the antecedent conditions after the rain on Friday and the
sensitivity over/near burn scars in the southeast portion of the state.

Bann


Day 2
Valid 12Z Sun May 04 2025 - 12Z Mon May 05 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PARTS OF THE
EASTERN UNITED STATES AND SOUTHERN ROCKIES AND ADJACENT HIGH PLAINS...

The risk of excessive rainfall persists across parts of the Mid-
Atlantic and Southeast US as a slow moving closed low embedded
within a broader upper trough continues to make its way eastward. Deepest moisture of 1.25 to 1.5 inches will be eventually be shunted off-
shore late in the period. Until then...isolated downpours are
possible with spaghetti plots of 2 and 3-inches of rain in 24 hours
mainly being produced by models with the ARW core...but enough
members from the NMM core and from the GEFS to warrant a Marginal.
The western boundary of the Marginal was trimmed compared with the
previous outlook given the models being more progressive with the
surface cold front and the push of drier air being brought in
behind the front.

There is also a Marginal Risk area over parts of New Mexico again
as moisture continue to spread northward and westward from the
Gulf. After 00Z...the flow aloft between the westerly subtropical
jet and a jet streak and low- and mid-levels become increasingly
diffluent with height falls beginning ahead of an approaching
closed low from the west. This...along with moisture and a low
level boundary already in place...should support late day and
evening storms that may produce locally heavy rainfall rates.

Bann


Day 3
Valid 12Z Mon May 05 2025 - 12Z Tue May 06 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE HIGH PLAINS ADJACENT TO THE SOUTHERN ROCKIES...

Shortwave energy rotating around the periphery of an upper low
making its way over the Southwest US will trigger late day
thunderstorms on Monday over parts of West Texas that grow upscale
in terms of both coverage and rainfall amounts through much of
Monday night/early Tuesday morning. A feed of low level moisture
being forced upslope ahead of the approaching shortwave will help
fuel the potential for downpours and locally heavy rainfall amounts
leading to the potential of flash flooding. QPF from the
operational models have maximum amounts of rainfall in the 2.5 to
3.8 inches...which tended to be supported by the SREF and GEFS
spaghetti plots and by machine learning first guess EROs. Felt a
Slight Risk area covers the potential for time being.

Bann

$$
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FOUS30 KWBC 040831
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
431 AM EDT Sun May 4 2025

Day 1
Valid 12Z Sun May 04 2025 - 12Z Mon May 05 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE HIGH PLAINS ADJACENT TO THE SOUTHERN ROCKIES...

New Mexico...
There is a slight risk of excessive rainfall over portions of
eastern New Mexico as south to southeasterly flow draws moisture
into the region as height falls begin in response to shortwave
energy approaches. The 04/00Z suite of numerical guidance develops
heavy rainfall developing in the diurnal activity that then
persists over the southern High Plains well into late tonight/early
Monday morning. Precipitable water anomaly values reaches 2 sigma
over this area by 00Z Monday..with the 04/00Z HREF mean suggests
some repeating threats for 1"/hr rates across the Slight area with
potential for 2-3" over much of the area. The eastern portion of
the Marginal risk area was largely left unchanged...but the western
portion of the area was trimmed to minimize overlap with heavy
snow areas (especially over the San Juan mountains).

Great Basin...
While the probability of excessive rainfall is likely non-zero
given the showery nature of precipitation given the upper trough
and cold mid- level temperatures aloft...the amount of rain
shouldn't be a problem unless it all falls in under an hour.
Individual thunderstorms may result in briefly heavy
rates...but thinking is that the thunderstorms will be embedded
within a broader field of showers circulating around the main upper
low. This should help mitigate the overall threat of flooding.

Midwest to Northeast...
The slow moving closed low embedded within a broader upper trough
continues to make its way eastward across the Ohio Valley today and
tonight. Deepest moisture of 1.25 to 1.5 inches will be eventually
be shunted off the Mid- Atlantic coast today but still stream in
over New York back and then drawn back through northern Ohio. The
Marginal Risk is maintained with only nudges to the
western/northern periphery of the Marginal risk area based on the
latest QPF.

Bann


Day 2
Valid 12Z Mon May 05 2025 - 12Z Tue May 06 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHERN HIGH PLAINS...

Texas into New Mexico...
A closed upper low over the Desert Southwest will continue to
meander eastward on Monday. Confidence remains in a focused area
for repeating heavy rainfall south from the TX Panhandle to the NM
border where a Slight Risk remains without many changes...with main
activity occurring once again around the time of maximum daytime
heating and then persisting into or through the night. The suite
of 04/00Z numerical guidance still shows the magnitude of
precipitable water values to exceed 2 sigma by 00Z Tuesday with the
1.25" precipitable water line reaching the Caprock. The 12Z QPF
consensus is for 2-4" over a sizable area just south of the TX
Panhandle...with locally higher amounts embedded in the broader QPF area.

Mojave Desert through Southern Utah...
Numerous showers with embedded daytime and evening thunderstorms is
still expected as upper low continues to meander over Arizona as
it begins to fill. Moisture is still anomalous for this time of
year...being some 2 to 3 standardized anomalies above climatology
for early May...but concern would be greater for excessive rainfall
if the actual values of precipitable water values were greater and
intense rainfall rates would be sustained for a longer duration.
As a result...the risk of excessive rainfall appears to be non-zero
but not enough to warrant a Marginal risk area based on
coordination with local offices.

Northern Mid-Atlantic into southern New England...
Closed low will continue to meanders across portions of the Upper
OH Valley through Monday night. Continued onshore flow brings the
threat for repeating locally heavy rain over the northern Mid-
Atlantic into southern New England which will have seen some heavy
rain between now and then. A Marginal Risk is maintained.

Bann


Day 3
Valid 12Z Tue May 06 2025 - 12Z Wed May 07 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHERN MISSISSIPPI VALLEY/CENTRAL GULF COAST REGION...

Showers and thunderstorms capable of producing intense rainfall
rates and heavy/excessive rainfall will become more numerous
on Tuesday as height falls make their way out across Texas and as
the parent upper low ejects out over the Southern Plains. With
increasing flow off the Gulf drawing deeper moisture on-
shore....the convection should become increasingly efficient
rainfall makers.especially over portions of Louisiana and
Mississippi. There is still some differences in where models place
the heaviest rainfall...with the GFS and Canadian favoring a faster
solution while the EC/UK favoring the axis from eastern Texas into
northern Louisiana. This forecast cycle nudged the Moderate risk
area a bit eastward but not as far east as the GFS/Canadian.

Bann

$$
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FOUS30 KWBC 112029
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
429 PM EDT Sun May 11 2025

Day 1
Valid 16Z Sun May 11 2025 - 12Z Mon May 12 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER MUCH OF THE SOUTHEAST...

16z Update: The best signal for isolated to scattered flash
flooding this afternoon/evening appears to be over portions of
southeast GA into northeast FL where backbuilding cells will result
in rainfall locally over 3 inches. In fact both 12z HREF and 06z
REFS neighborhood probabilities of exceeding 5" are over 50%, and
if/where this occurs would expect at least some minor flood
concerns to develop.

By this afternoon convection should develop over portions of
central AL into MS closer to the deep layer low center. This
activity will also likely exhibit some training/backbuilding
characteristics resulting in an isolated to scattered flash flood
risk. Some localized exceedance of 3" appear probable here, and
both the HREF and REFS indicate some FFG exceedance probs as well.
The Slight risk was expanded a bit to the west to account for this
activity over MS.

The northern edge of the Slight risk over the Carolinas was
tightened a bit as the main flash flood risk here will likely be
on day 2 (after 12z Monday). The Marginal risk was expanded
southward to include the rest of the FL peninsula as slow moving
convection may try to move into south FL overnight.

Chenard

...Previous Discussion...

A stationary upper low will remain positioned over the Central
Gulf Coast today while waves of upper level energy pivot around it
over the Southeast. The low is expected to become slightly
elongated north to south, resulting in strong southerly mean flow
that will pump moisture from the Gulf directly into the Southeast. Additionally, a southern stream jet is forecast to strengthen over
the northern Gulf, creating favorable upper level divergence over
North Florida and Georgia to support widespread shower and
thunderstorm development. At the surface, an occluded low pressure
system will be slowly moving north across the region, with a cold
front extending south across the Florida Panhandle and a stationary
front extending east across Georgia and South Carolina. The best
conditions for heavy rain will be in the warm sector over North
Florida and southern Georgia, but heavy rainfall will also be
possible along and north of the stationary boundary up into
portions of the Carolinas.

With plentiful moisture (PWATs 1.5-2+ inches) and instability
(MUCAPE 1500-2000+ J/kg), storms in the warm sector will be capable
of producing 2-3+ inch per hour rain rates from Florida to South
Carolina, which could lead to some flash flooding concerns given
2-3 inch per hour FFGs. Flash flooding may also be a concern back
into portions of Alabama and northern Mississippi where there will
likely be enough moisture and instability in the vicinity of the
surface low to produce showers and storms with 2+ inch per hour
rain rates. Previous heavy rains have already saturated soils from
Mississippi to Georgia, which will make these areas more sensitive
to flooding with additional heavy rain today. To account for this
flood potential there is a Slight Risk of excessive rainfall in
place for much of the Southeast, including areas from North Florida
to southern North Carolina and much of Alabama and northern
Mississippi. The Slight Risk area is encompassed by a broader
Marginal Risk that includes much of the Tennessee Valley, eastern
Arkansas, upslope regions of the southern Appalachians, and Central Florida.

Dolan


Day 2
Valid 12Z Mon May 12 2025 - 12Z Tue May 13 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHEAST AND SOUTHERN MID-ATLANTIC...

20z Update: Continue to be very close to needing a MDT risk
upgrade across the upslope areas of the southern Appalachians, but
we will hold at a higher end Slight risk for now. Orographically
enhanced rainfall and embedded convective elements periodically
pushing rainfall rates over 1"/hr will likely drive at least a
minor flash flood risk across this portion of the western
Carolinas and southwest VA. However confidence on seeing more
significant higher end impacts remains lower. With easterly low
level flow in place over this corridor the better instability may
tend to stay farther south over GA/SC and over the eastern
Carolinas. Probabilities of exceeding 1"/hr in the HREF peak
around 40-50% in the 12z HREF and REFS, likely indicative of some
exceedance, but probably not widespread. It will likely take these
higher rates of 1-2"/hr or greater to drive more significant impacts.

The currently forecast 3-7" of rainfall, combined with
embedded rates of 0.5"-1"/hr should be enough to drive at least
scattered instances of minor flash flooding, with localized more
significant impacts still possible. For now the expectation of
scattered minor flash flood and localized higher end impacts falls
more into the high end Slight risk category. If confidence in
greater coverage of higher rainfall rates increases, that would in
turn increase the potential for higher end impacts and justify a
MDT risk upgrade. Will thus continue to closely monitor.

The southeastern FL urban corridor is another area of concern for
flash flooding Monday. Neighborhood probability of exceeding 8"
are over 50% in both the 12z HREF and REFS and some deterministic
members are over 10". Overall seems like a favorable synoptic
setup for training convection and thus higher end urban impacts
are possible. Not confident enough yet to go with a MDT risk
upgrade, however do consider this a higher end Slight risk and the
potential is certainly there for significant urban impacts. We
will continue to monitor observational and model trends.

Chenard

...Previous Discussion...

The nearly stationary upper low that impacted the Southeast over
the weekend will finally gain some momentum and shift north towards
the Tennessee Valley on Monday, pulling the surface low pressure
system along with it. The trailing cold front will gradually push
towards the Southeast Atlantic Coast while the warm front lifts
into the southern Mid-Atlantic, and another round of widespread
showers and storms are forecast Monday into Monday night in the
warm sector of the system. Deep moisture will surge north ahead of
the cold front, extending from Florida through the Carolinas to
southern and central Virginia. PWATs are anticipated to reach
1.5-2+ inches in these areas with even higher values possible over
the Florida Peninsula. Strong south-southeasterly mean flow will
remain in place, which will likely result in two convergent zones,
one along the Southeast Coast and one along upslope regions of the
southern Appalachians where high QPF totals will be possible.
Strong diurnal convection over the Florida Peninsula will also
contribute to high QPF values over portions of Central and South Florida.

The largest flooding concerns will come with repeat/training
activity, which could result in high QPF totals over a relatively
short period of time, potentially reaching or exceeding the 1 and 3
hour FFGs in these regions. To account for this flash flood risk,
there is a Slight Risk area stretching from Florida up the
Southeast Coast to North Carolina and southern Virginia and also
for the upslope regions of the Appalachians from Georgia to
Virginia. A Marginal Risk area extends even further into the Mid-
Atlantic where moderate rain rates may contribute to localized
flash flooding and into the Tennessee and Mid-Mississippi Valleys
where enough moisture will likely wrap around the surface low to
create locally heavy rainfall in showers and storms.

Upslope regions of the southern Appalachians are particularly
sensitive to heavy rain, especially in areas that were impacted by
Hurricane Helene. Impacts from heavy rain on Monday will likely
fall into the high-end Slight Risk category, and ERO upgrades may
be needed in the future if high QPF trends hold,. However,
instability may be a limiting factor as the better instability is
expected to reside along the coast. After coordinating with local
forecast offices, it was decided to hold off on any upgrades at
this time. By this afternoon, the CAMs will go out far enough to
cover the entire Day 2 period and will likely give us a better idea
of the magnitude of potential flooding impacts.

Dolan

$$
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FOUS30 KWBC 120803
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
403 AM EDT Mon May 12 2025

Day 1
Valid 12Z Mon May 12 2025 - 12Z Tue May 13 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER SOUTHEAST FLORIDA...

A deep upper low will be slowly moving north towards the Tennessee
Valley, dragging a surface low pressure system north with it. The
trailing cold front will gradually push towards the Atlantic Coast
while the warm front lifts north into the southern mid-Atlantic.
This system will direct a stream of deep anomalous moisture into
the Southeast and Mid-Atlantic that will support widespread showers
and storms with heavy rain potential across these regions. PWATs
are expected to surge to over 1.5 inches from Virginia to Georgia
and over 2 inches over the Florida Peninsula, which will certainly
provide the needed moisture for elevated rain rates in stronger convection.

A Moderate Risk area has been introduced for the urban corridor of
Southeast Florida where heavy rain may result in significant
flooding impacts. The synoptic setup is favorable for a heavy rain
event over South Florida with deep moisture and southerly winds
shifting to southwesterly ahead of an approaching cold front. Waves
of showers and storms are expected throughout the period, and
there will be plenty of moisture and instability to support high
rain rates in excess of 2 inches per hour. CAMs are showing the
potential for 3-4, locally up to seven, inches of rain possible
today. Yesterday's 18Z HREF was showing 60-70% probability of 24
hour QPF exceeding 8 inches, but the 00Z HREF dropped probabilities
of 8 inches in 24 hours down to 40-50%, indicating some
uncertainty in how high the max QPF amounts may be. Regardless of
the exact amount, flooding impacts are likely for the urban
corridor of Southeast Florida.

To the north, strong south-southeasterly mean flow will focus QPF
maxes along the Carolina Coast and along upslope regions of the
southern Appalachians. CAMs have consistently shown 2-4 inches of precipitation, with locally higher amounts possible, over the 24
hour period in these areas. There was discussion about potentially
upgrading to a Moderate Risk for sensitive areas in the
Appalachians, but it was decided to remain at a high-end Slight
Risk given a lack of instability and limited rain rates. Rain rates
could periodically exceed 1 inch per hour, which would support
isolated to scattered flash flooding concerns for the western
Carolinas and Southwestern Virginia, but most likely would not
support a risk higher than Slight. The higher rain rates (1-2
inches per hour) are expected to be in convection near the coasts
where instability will be higher.

To cover these flooding threats, a Slight Risk area extends from
Virginia to the Florida peninsula. There will also be localized
heavy rain potential across the Tennessee and Mid-Mississippi
Valleys, Mississippi, and Alabama. There will be decent instability
in the vicinity of the surface low to produce convection with 1
inch per hour rain rates. Given that soils in these regions are
saturated from recent heavy rains, isolated flooding concerns will
be possible, and therefore a Marginal Risk of excessive rainfall is
in place.

Dolan


Day 2
Valid 12Z Tue May 13 2025 - 12Z Wed May 14 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE MID-ATLANTIC...

The slow-moving upper low and occluded surface low will continue
to move north, and showers and storms will focus across the Mid-
Atlantic on Tuesday. Deep moisture ahead of the system will push
PWAT values above 1.5 inches, and there will be enough instability
(MUCAPE > 1500 J/kg) across portions of North Carolina and Virginia
to support high rain rates (1-2 inch per hour), which may rival 1
and 3 hr FFGs. Upslope flow along the Appalachians from southern
Pennsylvania through Virginia will also help to enhance rainfall,
with generally 1.5-2.5 inches of rain expected across this area
with locally higher amounts possible. After heavy rain on Monday,
these areas may be more sensitive to flooding given higher soil
moisture, and isolated to scattered flash flooding concerns are
expected. This will warrant a continuation of the Slight Risk area
from northeastern North Carolina through Virginia and portions of
West Virginia, Maryland, and southern Pennsylvania.

Isolated flash flooding may also be possible for portions of the
Ohio Valley and Appalachians. Moisture wrapping around the northern
side of the low pressure system combined with sufficient
instability near the surface low will support scattered convection
with relatively slow storm motion. Therefore, a Marginal Risk is in
place for these regions.

Dolan


Day 3
Valid 12Z Wed May 14 2025 - 12Z Thu May 15 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE NORTHERN PLAINS AND MID-ATLANTIC...

...Northern Plains...

A deep upper level trough will push across the Northwest to the
Plains on Wednesday, resulting in a strengthening low pressure
system in the northern Plains. Stratiform rain with likely some
embedded convection on the northern and western side of the low are
forecast to produce 0.5-1 inches of rain, with locally higher
amounts possible, in eastern Montana and northeastern Wyoming. The
main threat will be due to the persistent nature of the
precipitation in this area, starting up Tuesday night and
continuing through Wednesday into Wednesday night. Rainfall totals
will likely come close to the 6 hour FFGs in eastern Montana.

For the Dakotas, convective precipitation is forecast to develop
ahead of the low along a strengthening frontal boundary. Models are
in good agreement on the axis of heaviest precipitation setting up
over central North Dakota and eastern South Dakota. PWAT values
are expected to be at least 2 standard deviations above normal
(1-1.5 inches), and there should be enough instability (MUCAPE >
1500 J/kg) during the day on Wednesday to support at least an
isolated flash flood threat.

...Mid-Atlantic...

Soils are expected to be thoroughly saturated across the Mid-
Atlantic after heavy rain on Monday and Tuesday, which may create a
low end flood threat with lingering showers on Wednesday. The
slow-moving surface low is forecast to track right over the Mid-
Atlantic with scattered precipitation, and there should be enough
instability near the low to support some convection capable of
producing locally heavy rain. Therefore, a Marginal Risk area was
introduced for portions of the Mid-Atlantic.

Dolan

$$
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FOUS30 KWBC 130748
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
348 AM EDT Tue May 13 2025

Day 1
Valid 12Z Tue May 13 2025 - 12Z Wed May 14 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE MID-ATLANTIC...

A closed upper low will gradually lift north over the Tennessee
and Ohio Valleys, accompanied by a very slow-moving surface low
pressure system. A stream of deep Gulf/Atlantic moisture will move
into the Mid-Atlantic ahead of the system, increasing PWAT values
to 1.5-2 inches. There will be enough instability (MUCAPE > 1500
J/kg) to support thunderstorm development, some of which may be
strong/deep. The best chances for deep convection with high rain
rates (1-2 inches) will likely be over portions of Virginia and
eastern North Carolina where higher instability will reside, but
persistent upslope enhancement will also contribute to elevated
rain rates over portions of the Appalachians from central and
southern Pennsylvania to Virginia. These areas will likely see 1-3
inches of rainfall today, with locally higher amounts in terrain
and heavier convection. Heavy rain will have the potential to
create isolated to scattered flooding concerns across these areas,
warranting a Slight Risk of excessive rainfall.

Elsewhere, a Marginal Risk of excessive rainfall is in effect for
the Ohio Valley and portions of the Tennessee Valley and interior
Southeast where scattered diurnal convection is expected underneath
the upper low. Slow storm motion will contribute to elevated rain
rates (1+ inch per hour) that could reach or exceed 1 and 3 hour
FFGs (1-2 inches). Given that soils in these areas are already
saturated from recent heavy rain, these rain rates could create
isolated instances of flash flooding.

Dolan


Day 2
Valid 12Z Wed May 14 2025 - 12Z Thu May 15 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE NORTHERN PLAINS AND MID-ATLANTIC...

...Northern Plains...

A deep upper level trough will push across the northern Rockies
into the northern Plains late Tuesday into Wednesday, resulting in
a strengthening low pressure system tracking from Wyoming through
North Dakota. Stratiform rain with some embedded convection is
expected on the northern and western side of the low, which should
result in a swath of 0.5-1+ inches of rainfall across central and
eastern Montana on Wednesday. Storm total rainfall will be higher
across Montana due to additional rain falling at the end of the Day
1 period (Tuesday night). The main concern with this activity will
be the duration, with rainfall rates potentially reaching 6 hour
FFGs. This could support isolated flash and river flooding concerns.

Over the Dakotas, convection is expected to develop along a
strengthening cold front that will push east across the region.
With favorable upper level and surface support, some convection may
be deep enough to produce 1+ inch per hour rain rates that could
reach or exceed the 1 and 3 hr FFGs (around 1.5-2.5 inches).
Conditions will be supportive of localized heavy rain in stronger convection/thunderstorms, with plentiful moisture (PWATs 1-1.5
inches) and instability (CAPE > 1500 J/kg) in place. The Marginal
Risk of excessive rainfall in the northern Plains includes portions
of Montana and the Dakotas where isolated to potentially scattered
instances of flash flooding will be possible. It's possible an
upgrade may be needed for the Dakotas if precip rates and QPF trend
higher, but we should have a better idea of potential impacts once
the period is fully within range of the CAMs.

...Mid-Atlantic...

Soils are expected to be thoroughly saturated across the Mid-
Atlantic by Wednesday due to heavy rain earlier in the week, which
will likely result in a lingering flash flood threat on Wednesday.
The slow-moving surface low is forecast to become nearly stationary
over the region while gradually weakening, resulting in scattered
precipitation through Wednesday night. Enough moisture and
instability are expected in the vicinity of the surface low to
support convection with relatively higher rain rates that could
lead to flooding. The 00Z HREF shows a high probability (60-80%) of
1 inch per hour rain rates from the Maryland and West Virginia
Panhandles through Virginia to eastern North Carolina and even a
low/isolated probability (~20%) of 2 inch per hour rain rates. A
Marginal Risk is in place from southern Pennsylvania through North
Carolina to northeast South Carolina to account for this flood
potential.

Dolan


Day 3
Valid 12Z Thu May 15 2025 - 12Z Fri May 16 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE UPPER MIDWEST AND NORTHERN PLAINS...

An occluded low pressure system will lift northeast across the
Upper Midwest, with showers and storms ahead of the occluded and
cold fronts and some precipitation wrapping around the backside of
the system into the northern Plains as well. Slow storm motion and
repeat activity look like they will be the main threat, which may
result in rain rates that may reach or exceed the 3 hour FFGs.
There will be plenty of moisture in place to support elevated rain
rates with PWAT values reaching 1-1.5 inches. However, instability
may be a limiting factor. The best instability is expected to be
further south along the cold front, displaced from the higher QPF
values. Based on available guidance, a Marginal Risk area should
suffice to account for the low end flash flood potential.
Precipitation is forecast to extend across the Great Lakes region
as well, but rain rates will likely be moderate at best, not
supporting a flash flood threat at this time.

Dolan

$$
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FOUS30 KWBC 140733
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
333 AM EDT Wed May 14 2025

Day 1
Valid 12Z Wed May 14 2025 - 12Z Thu May 15 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE NORTHERN PLAINS AND MID-ATLANTIC...

...Northern Plains...

A deep upper level trough centered over the Intermountain West this
morning will become negatively tilted as an impressive shortwave
draws plentiful upper level energy into the northern Plains.
Surface cyclogenesis is expected ahead of this trough over Kansas,
which will track NNE into south-central North Dakota by Thursday
morning. A line of convection associated with the leading/eastern
edge of the trough is moving into far western South Dakota from
Wyoming, and this line of storms will track NNE over the western
Dakotas through the morning. The primary flooding threat will be
from a new line of storms which will develop over western South
Dakota with peak heating this afternoon, then track very slowly
eastward, as embedded cells move north, parallel to the line. This
will result in some training of convection, leading to an isolated
flash flooding threat.

In coordination with UNR/Rapid City, SD; FSD/Sioux Falls, SD; and
ABR/Aberdeen, SD forecast offices, the inherited Slight Risk was
removed with this update, and the surrounding Marginal shifted well
to the west of inherited. The westward shift was due largely to a
shift in the guidance slowing the forward motion of the trough.
While this increased forecast rainfall amounts some, the area of
the Dakotas now highlighted is in Moderate to in some localized
cases Severe drought. Nasa Sport soil moisture imagery shows the
area has next to no moisture. Thus, despite the potential for heavy
rainfall at times in some areas, the flooding threat was determined
to be isolated.

...Mid-Atlantic...

Lingering moisture from a slow moving storm system associated with
a weak upper level negatively tilted trough along with MUCAPE
values in the area between 1,000 and 1,500 J/kg this afternoon will
lead to a renewed round of showers and thunderstorms across much of
the Mid-Atlantic. Due to the movement of the trough however, the
storms should be rather progressive, which will limit the amount of
rainfall any one area sees. While the entire area has picked up 1-2
inches of rain yesterday, thoroughly saturating the near-surface
soils, expect most areas to see less than an inch of new rain.
Those localized areas under the stronger storms may perhaps
approach an inch of new rainfall. This should keep flash flooding
isolated and localized, albeit with some uncertainty. For now the
area remains in a higher end Marginal with few changes from
inherited. 00Z HREF guidance shows a high probability of exceeding
3 and 6 hour FFGs from far western Maryland southeast to the
Tidewater of Virginia with these storms and low FFGs, but it
remains unclear as to the impacts from the resultant flooding given
the significantly lower amounts of rain expected today as compared
with yesterday.

Wegman


Day 2
Valid 12Z Thu May 15 2025 - 12Z Fri May 16 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE NORTHERN PLAINS...

The low over the northern Plains will become vertically stacked as
the upper trough catches up with the surface low. With the new
vertically stacked low moving only very slowly towards the
northeast, this will make for a prolonged period of rain on the
cold/northwest side of the center, as it becomes the comma head
region of the low. This area of the low is expected to be largely
devoid of convection given the lack of instability making it quite
that far north and west. Thus, expect the 2-3 inches of additional
rainfall from today to have only a minimal impact given the still
largely dry soils over much of North Dakota. This Marginal was
shifted well to the west following the latest guidance trends, so
the Marginal was removed from much of Minnesota due to lack of
expected rainfall.

Wegman


Day 3
Valid 12Z Fri May 16 2025 - 12Z Sat May 17 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE MIDWEST, TENNESSEE VALLEY, AND OZARKS...

A potent shortwave trough will round the periphery of the
vertically stacked low over the northern Plains and upper Great
Lakes on Friday. This shortwave will tap into a low level jet of
Gulf moisture riding the prior low's occluded front. This will
reinvigorate the front, resulting in rather fast northeastward
moving storms across the Marginal Risk area. Much of this area
remains saturated for soil moisture from recent prior storms, so
any training thunderstorms will be capable of producing isolated
flash flooding. There is poor agreement on the character of the
storms, which better agreement may have warranted a Slight Risk
upgrade in part due to the wet soils in this area. For now, will
continue to monitor the trends in the rainfall guidance for better
indication on if a Slight Risk upgrade is needed.

Wegman

$$
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FOUS30 KWBC 150804
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
404 AM EDT Thu May 15 2025

Day 1
Valid 12Z Thu May 15 2025 - 12Z Fri May 16 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
NORTHERN PLAINS AND MID-ATLANTIC...

...Northern Plains...

A well-developed low will track north into the eastern Dakotas into
this afternoon, with a slow and chaotic track through tonight. This
track is supported by a nearly stationary upper level low, with a
potent shortwave trough rounding its southern periphery, thus
increasing the divergence aloft. While the low itself will be able
to tap into some of the Gulf moisture across much of the eastern
half of the country, this is not expected to result in significant
flash flooding. For North Dakota, any associated instability is
likely to stay east of the low center. Meanwhile, the cold conveyor
belt feeding the comma-head region of the surface low will be
unable to also advect instability into the region. Thus, while the
24 hour rain forecast remains consistent with continuity with a
forecast for 2-3 inches of rain areally across western North Dakota
through 12Z Friday, the lack of instability will keep that
rainfall as stratiform, and therefore unlikely to cause flash flooding.

...Mid-Atlantic...

Multiple rounds of rainfall are likely to impact portions of the
Mid-Atlantic through this Day 1 period. This will be on the heels
of several days of more widespread heavy rain that has occurred
over the past few days. While today should be a wind down of the
coverage of heavy rain, it's still possible that any storms that
form today into tonight will merge together, train, or remain so
slow moving as to cause localized flash flooding. As an occluded
front associated with the low over the Northern Plains approaches,
it will turn the predominant storm track towards the east and
northeast. This will be a significant change in the storm motions
from previous days, and one that should ultimately keep any flash
flooding producing storms as few and far between. Since the soils
are very moist and prone to flash flooding, the lessening coverage
of storms over the area would still favor the continuation of the
Marginal Risk for today.

Wegman


Day 2
Valid 12Z Fri May 16 2025 - 12Z Sat May 17 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
OHIO VALLEY...

A stalled and shearing apart occluded front over the Ohio Valley
early Friday morning will dissipate through the day as its
associated rainfall ends. However, a reinforcing strong shortwave
will round the southern periphery of the vertically stacked low,
which will be pushing east from the Northern Plains and into the
upper Great Lakes. This shortwave and associated push of cooler air
in the form of a cold front will tap into the moisture and
instability largely in place ahead/southeast of the cold front over
the Ohio Valley, resulting in multiple areas of storms forming
Friday afternoon from southern Illinois through West Virginia.
While some training is possible as the storms are forming, they're
likely to develop into a single line, where any training would be
from pre-line convection that will likely be moving into and being
absorbed by the line. The line of storms will continue south into
the Mid-South through Friday night, albeit with lessening flash
flooding potential as the line becomes the only area of storms
around. As with areas further east, soil moisture levels all up and
down the Ohio Valley are at or above normal for this time of year,
and the presence of moisture to the order of 1.5 to 1.75 inches of
PWAT will support strong thunderstorms capable of 2+ inch/hour
rainfall rates. Given the sensitivities of the rivers and streams
in the area, the combination of heavy rain and sensitive soils
supported the continuance of the Slight Risk area, with some
expansions included to account for more the suite of guidance.

Wegman


Day 3
Valid 12Z Sat May 17 2025 - 12Z Sun May 18 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM CENTRAL
TEXAS THROUGH NORTHERN ALABAMA AS WELL AS FOR PORTIONS OF THE
NORTHEAST...

...Texas to Alabama...

Another round of afternoon and evening thunderstorms is expected
from northeast Texas into northern Alabama Saturday and Saturday
night. Continued influx of Gulf moisture and instability on
southerly flow will clash with the cooler, dry air mass behind a
cold frontal passage over much of the Midwest on Friday. The storms
will form along this frontal interface. With that said, the forcing
in the upper levels should be greatly reduced over this region as
compared with previous days, as the upper forcing on Saturday will
be associated with a fast moving and weaker shortwave. This should
limit the coverage of storms. Once again however, recent heavy
rains in this area continue to keep the soils wet, and therefore
more prone to flash flooding. Should the forcing increase or amount
of moisture off the Gulf increase compared to current forecasts,
then it's possible a targeted Slight may eventually be needed,
with the DFW Metroplex area currently appearing to be at greatest
risk for an upgrade.

...Northeast...

Periods of heavy rain will move across the Northeast Saturday
afternoon ahead of a potent upper level low moving across the Great
Lakes. The storms will occur ahead of the upper low. There is some
uncertainty on storm coverage and intensity with moisture amounts
being limited in this area, but it is made up for by wetter than
average soils in this area of New England and New York. The
inherited Marginal Risk was trimmed out of most of Maine, as soils
there are drier than normal, which should allow any rainfall (which
should be less than an inch) to be absorbed by the dry soils.

The greatest flash flooding risk is likely in the Green and White
Mountains where terrain will worsen any potential flash flooding.

Wegman

$$
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FOUS30 KWBC 160823
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
423 AM EDT Fri May 16 2025

Day 1
Valid 12Z Fri May 16 2025 - 12Z Sat May 17 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
OHIO AND TENNESSEE VALLEYS ALONG WITH WESTERN MAINE...

...Arklatex into the OH/TN Valleys...
A very active day convectively is expected across large areas of
the OH/TN Valley region as a deep layer closed low and associated
trough ejects east across the Upper Midwest which will drive a
cold front gradually southeastward through this afternoon and
evening. A very unstable airmass is expected to pool across much of
the Mid- South and OH Valley region in general with MLCAPE values
likely to reach as high 2500 to 4000+ J/kg while coinciding with a
significant amount of deep layer shear. Much of the shear will be
associated with stronger 500/700 mb wind fields rounding the
southeast flank of the aforementioned upper-level trough with
associated jet energy. An EML is already showing up in regional 00Z
RAOB soundings and is at least suggested in GOES-E low-level WV
imagery early this morning. And this coupled with strong warm air advection/boundary layer heating ensuing by midday and along with
deeper layer jet-aided ascent, very strong/severe- mode convection
is likely to develop which will include a threat for supercells
across areas of the OH/TN Valley region.

Cell-merger activity and localized training of these organized
clusters of convection is expected which aside from the severe mode
of the convection will support concerns at least scattered areas
of flash flooding. In fact, the 00Z GFS shows a corridor of strong
850/700 mb moisture flux anomalies taking aim on KY and TN in the
18Z to 06Z time frame, and the 00Z HREF guidance along with recent
HRRR/RRFS runs suggest areas of especially central/southern KY and
northern TN seeing as much as 2 to 4+ inches of rain as these
clusters of convection eventually become aligned in a more linear
fashion with QLCS evolution expected in time. Moist/wet antecedent
conditions will favor locally enhanced runoff concerns with these
rainfall totals. The Slight Risk area has been adjusted a bit
farther south and southwest compared to continuity to account for
the overall organized convective footprint and with locally high
rainfall rate (1 to 2+ inch/hour rates) expected. The Marginal Risk
area has been expanding as far southwest as the Arklatex vicinity.

...Mid-Atlantic/Northeast...
A more uncertain evolution of convection is expected today and
tonight for much of the Mid-Atlantic and Northeast. Initially,
strong warm air advection and shortwave energy lifting across the
lower Great Lakes/northern Mid-Atlantic region early this morning
may favor some scattered clusters of fairly organized shower and
thunderstorm activity, but the latest hires model guidance shows a
fair amount of disagreement with overall rainfall amounts and
placement early this morning as this energy lifts off to the
northeast. However, in the 18Z to 00Z time frame, the arrival of
additional shortwave energy/divergent flow aloft and greater
instability is expected to favor scattered areas of redeveloping
convection that will be possible across portions of the northern
Mid-Atlantic and also northward into central and northern New
England in close proximity to a warm front that will be riding
northeastward. This will include a threat for locally slower-moving
and more concentrated convective cells over some of the higher
terrain, including western Maine. The 00Z HREF guidance suggests
some pockets of 2 to 3 inch rainfall totals with some locally
elevated 3-hour FFG and 5-year ARI exceedance probabilities being
depicted here. Some isolated to scattered areas of flash flooding
cannot be ruled out given the moist/unstable environment favoring
high rainfall rates and some of these locally heavier storm totals.
As a result, the Marginal Risk of excessive rainfall has been
expanding into the Northeast with a Slight Risk introduced over the
higher terrain of western Maine.

Later tonight, the central Mid-Atlantic also may become a target
for additional convection as the upstream QLCS activity over the
OH/TN Valley region arrives, and with already sensitive/wet
antecedent conditions here, additional localized flash flooding
concerns will be possible. The Marginal Risk area has been
expanded to include much of the central and northern Mid-Atlantic.

Orrison


Day 2
Valid 12Z Sat May 17 2025 - 12Z Sun May 18 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM CENTRAL TEXAS
THROUGH CENTRAL ALABAMA AS WELL AS FOR PORTIONS OF THE NORTHEAST...

...Texas to Alabama...
Convection will likely develop across portions of central TX
Saturday afternoon as increasing forcing overruns the dryline.
Enough mid level vort energy, upper jet support and robust
instability to support likely upscale growth of convection as it
moves into northeast TX. The extent of the flash flood risk will
likely come down to convective longevity at any one location as
cells should be pretty fast moving. This fast movement may limit
the areal coverage of flash flooding, however certainly an
opportunity for at least some training as convection grows upscale.
The 00z CAMS and AIFS suggest northeast TX towards the AR/LA
border has the best chance of seeing convective training
potentially leading to a flash flood threat. Overall still not
enough model support to suggest Slight risk coverage, but localized
flash flooding appears probable with this setup, especially over
more sensitive urban areas. Areal averaged rainfall may only
average around an inch, but would expect to see localized totals
around 3", much of which would fall in just a couple hour period.

Convection will likely be ongoing across the eastern portion of the
Marginal risk (MS/AL) at 12z Saturday, but likely in a decaying
state. However we could see at least isolated to scattered
redevelopment along the leftover outflow during the day Saturday,
and anything that does develop would likely be slow moving and
capable of resulting in a localized flash flood threat.

...Northeast...
A couple rounds of convection appear likely across the Northeast
on Saturday...one in the morning and another by afternoon/evening.
Both rounds are expected to feature quick moving cells with deep
layer mean flow over 30 kts. This will likely limit the extent of
any flash flood risk, however localized 1" in an hour amounts are
still probable given the moisture and instability forecast. These
higher rates combined with the potential for multiple convective
rounds supports an isolated flash flood threat and a continued
Marginal risk area.

Chenard


Day 3
Valid 12Z Sun May 18 2025 - 12Z Mon May 19 2025

...THERE IS SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE
CENTRAL PLAINS INTO THE LOWER AND MIDDLE MISSISSIPPI VALLEY...

...Plains, MS Valley and Southeast...
A favorable pattern for widespread convection and heavy rainfall
on Sunday across the middle portion of the country. A longwave
trough and embedded shortwaves pushing eastward across the Rockies
and into the Plains will provide ascent over a broad region. The
frontal pattern will likely feature a developing low moving into
the High Plains of CO/NE, a warm or stationary front extending east
of this low across portions of KS into MO/AR, and a dryline across
OK/TX. A large pool of instability is expected east of the dryline
and south of the stationary front, with values upwards of
4000-5000 j/kg. Some convection may be ongoing near the
warm/stationary front Sunday morning, but more robust development
is expected by Sunday afternoon into the overnight hours as
stronger forcing ejects into the Plains.

The main area of focus for flash flooding appears to be across
portions of eastern KS into MO and/or AR near the aforementioned stationary/warm front. Convection should first develop over central
KS with upscale growth into an MCS likely. Mean flow is off to the
northeast, however with a strong southwesterly low level jet,
Corfidi vectors are pointed more towards the southeast. Thus would
expect convection to turn easterly and then southeasterly as it
organizes Sunday evening. As this process occurs some
training/backbuilding on the south/southwest extent is probable
resulting in a scattered flash flood threat. The exact MCS
location/track remains uncertain, but think the 00z GFS is likely
too far to the north and east...with the aforementioned expected MCS propagation taking it on a farther southern track. Thus tend to
think something closer to the 00z ECMWF and UKMET is more likely.
The experimental 00z RRFS (the first CAM to go out into day 3) also
seems to show a plausible evolution and placement over eastern KS
into western MO. The setup does have the potential for a swath of
over 5" of rainfall where training/backbuilding ends up being
maximized. Thus this is trending towards a higher end Slight risk,
with at least scattered flash flooding probable.

Another area of interest will be farther northwest into western NE
and southwest SD, closer to the low track. A multi-model signal
exists for a second QPF max over this area...which makes sense given
what should be impressive synoptic driven ascent and instability
along the stationary/occluded front. Considered expanding the Slight
risk into this area...but opted against that for now. This area
remains in severe to extreme drought and was not ready to go with a
large Slight risk area yet. But we will continue to monitor trends
and an expansion of the Slight risk may eventually be necessary.

A localized flash flood risk also exists both along the dryline from
central TX into OK...and over the Southeast where a lingering
boundary and substantial instability will support heavy rainfall
with any storms that area able to develop.

...Northeast...
A Marginal risk continues over portions of northern New England on
Sunday as a deep layered low remains overhead. This will be the
3rd straight day of localized heavy rainfall, and thus some areas
may be more sensitive by this time. Generally thinking both
instability and moisture will be lower by Sunday, however cold air
aloft under the low will likely still support some heavier
convective cells and an isolated flash flood risk.

Chenard

$$
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FOUS30 KWBC 170832
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
432 AM EDT Sat May 17 2025

Day 1
Valid 12Z Sat May 17 2025 - 12Z Sun May 18 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
NORTHERN NEW ENGLAND...

...Texas to Alabama...
Convection will likely develop across portions of central TX this
afternoon as increasing forcing overruns the dryline. Pretty
impressive thermodynamic environment, with upwards of 5000 j/kg of
CAPE forecast along and east of the dryline, along with substantial
deep layer shear. This will likely result in rather explosive
convective development this afternoon, and while not the strongest
large scale forcing, there is enough mid level vort energy and
upper jet dynamics to support scattered to perhaps numerous
convective coverage. Supercells are likely, with some upscale
growth into convective clusters probable. Given the CAPE/shear
profile, large hail is the main threat, although even with such a
robust CAPE profile the deep layer moisture is actually still
pretty good. Thus these cells will likely be capable of producing
some heavy rainfall rates over 2"/hr as well.

Limiting factor for flash flooding will be quick cell motions
(30-40 kt mean westerly flow) and the high FFG over the area.
However right moving supercell motions are closer to 15-20 kts)
and the various cell movement deviations we see in a supercell
environment will likely lead to some cell mergers as well. Thus do
think we will see isolated flash flooding, with a focus over
central to northeast TX. Not sure we will get the FFG exceedance
coverage needed for a Slight risk given the generally quick cell
motions and high FFG, so we will stick with a Marginal risk. Even
the 00z RRFS, which tends to run hot with QPF rates/totals, only
depicts isolated hourly FFG exceedance.

Convection will likely be ongoing this morning across the eastern
portion of the Marginal risk (MS/AL), but should be in a decaying
state. However we could see at least isolated redevelopment along
the leftover outflow/front this afternoon, and anything that does
develop would likely be slow moving and capable of resulting in a
localized flash flood threat.

The Marginal risk was also expanded to the north into more of OK/AR,
southeast KS and southern MO. There are indications that an
overnight cluster of storms should develop here later tonight into
Sunday morning. This is where the stronger moisture convergence and
instability gradient should be and thus it makes sense that we
would get some elevated convection develop somewhere along this
axis. The 00z HREF is not that aggressive with development here,
but the HREF members can often be slow in catching on to training
elevated convective development. There is enough of a signal in the
00z global guidance to suggest we may see the HREF trend wetter on
future cycles, and there is at least some threat of an isolated
flash flood risk.

...Northeast...
Multiple rounds of convection are expected across the Northeast
today into this evening. PWs and instability in place support high
rainfall rates, and both the 00z HREF and 18z REFS depict a 30-50%
chance of hourly rainfall over 1" and the 06z HRRR has a swath of
1- 2" per hour rainfall. In general, quick cell motions will help
limit the duration of these heavy rates, but the combination of
multiple convective rounds and high rates indicates at least some
flash flood risk is in place. Recent high res model runs indicate a stationary/warm front in place over portions of VT/NH this
afternoon, which may act as a focus for some short duration
training of cells. Expect the best chance for isolated to scattered
flash flooding to focus near and south of this boundary, which
ends up encompassing much of central/northern VT into central NH.
This is generally a bit south and west of the inherited Slight
risk area. Thus we will expand the Slight risk into this region,
while maintaining it in northern NH and western ME (less confidence
on higher rates in these latter areas, but heavy rainfall over the
past 24 hours may keep the area a bit more sensitive to additional
rainfall today).

Chenard


Day 2
Valid 12Z Sun May 18 2025 - 12Z Mon May 19 2025

...THERE IS SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE
CENTRAL PLAINS INTO THE LOWER AND MIDDLE MISSISSIPPI VALLEY...

...Plains, MS Valley and Southeast...
A favorable pattern for widespread convection and heavy rainfall
on Sunday across the middle portion of the country. A longwave
trough and embedded shortwaves pushing eastward across the Rockies
and into the Plains will provide ascent over a broad region. The
frontal pattern will likely feature a developing low moving into
the High Plains of CO/NE, a warm or stationary front extending east
of this low across portions of OK/KS into MO/AR, and a dryline
across OK/TX. A large pool of instability is expected east of the
dryline and south of the stationary front, with values upwards of
4000-5000 j/kg. Some convection may be ongoing near the
warm/stationary front Sunday morning, but more robust development
is expected by Sunday afternoon into the overnight hours as
stronger forcing ejects into the Plains.

The main area of focus for flash flooding appears to be near the
aforementioned warm/stationary front where some training of convection
is probable. The overall expectation is that robust convective
development occurs along/ahead of the dryline over central OK/KS
during the afternoon hours. Strong deep layer southwesterly flow
will likely quickly push this activity northeastward towards the warm/stationary front. Activity will likely grow upscale Sunday
evening into the overnight, potentially into an MCS, at which point
it should feel the impact of the strong southwesterly low level jet
and begin turning easterly and then southeasterly aligned with the
upwind Corfidi Vectors. As this process occurs some
training/backbuilding on the south/southwest extent is probable
resulting in a scattered flash flood threat.

The exact MCS location/track remains a bit uncertain. All but
certain that the 00z NAM is too far north, as its QPF evolution is
an outlier and does not align with pattern recognition. The GFS
and GEFS mean are also probably too far to the northeast, with the aforementioned expected MCS propagation taking it on a farther
south track. The 00z Gem Reg and RRFS are very far south, tracking
across eastern OK into central/northern AR. This may be too far
south, but can not be ruled out as easily as the farther north NAM
can. The AIFS has a track record of pinpointing organized
convection location quite well, and the 00z AIFS favors northeast
OK into southeast KS and southwest MO. This also happens to
generally be the middle ground of the other available models, and
so does appear to represent the most likely outcome at this time.
Thus a higher end Slight risk will remain in place across this
corridor, where scattered flash flooding is expected. The Slight
risk area was cut back a bit on its northern extent and expanded
to the southwest into more of OK and AR to account for the southern
trend. Can not rule out additional southward shifts/expansion..but
for now think the Slight risk area represents the general region
of most concern well.

Another area of interest will be farther northwest into central and
western NE, closer to the low track. A multi-model signal exists
for a second QPF max over this area...which makes sense given what
should be impressive synoptic driven ascent and instability along
the stationary/occluded front. Considered expanding the Slight risk
into this area...but opted against that for now. This area remains
in severe to extreme drought and possible the rainfall max ends up
over the high FFG sand hills. But we will continue to monitor
trends and an additional focused Slight risk may eventually be needed.

A localized flash flood risk also exists both along the dryline from
central TX into OK...and over the Southeast where a lingering
boundary and substantial instability will support heavy rainfall
with any storms that area able to develop.

...Northeast...
A Marginal risk continues over portions of northern New England on
Sunday as a deep layered low remains overhead. This will be the
3rd straight day of localized heavy rainfall, and thus some areas
may be more sensitive by this time. Generally thinking both
instability and moisture will be lower by Sunday, however cold air
aloft under the low will likely still support some heavier
convective cells and an isolated flash flood risk.

Chenard

$$
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FOUS30 KWBC 180815
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
415 AM EDT Sun May 18 2025

Day 1
Valid 12Z Sun May 18 2025 - 12Z Mon May 19 2025

...THERE IS SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE
CENTRAL PLAINS INTO THE LOWER AND MIDDLE MISSISSIPPI VALLEY...

...Plains, MS Valley and Southeast...

A favorable pattern for widespread convection and heavy rainfall
today across the middle portion of the country. A longwave trough
and embedded shortwaves pushing eastward across the Rockies and into
the Plains will provide ascent over a broad region. The frontal
pattern will likely feature a developing low moving into the High
Plains of CO/NE, a warm or stationary front extending east of this
low across portions of OK/KS into MO/AR, and a dryline stretching
from central KS into TX. A large pool of instability is expected east
of the dryline and south of the stationary front, with values
upwards of 4000-5000 j/kg.

Complicated convective evolution today into tonight, but the
greatest risk of flash flooding will likely be with any upscale
growth of convection that can occur this evening into tonight near
the warm/stationary front. There is a significant amount of spread
amongst the 00z HREF members and global guidance regarding
convective details today, supporting the idea of a lower confidence
forecast. However, while the confidence on the details may be lower
than normal for a day 1 forecast, there is decent confidence that
somewhere will see a more organized flash flood risk develop later
today into tonight.

The overall expectation is that robust convective development occurs
along and east of the dryline this afternoon from central TX into OK
and KS. The activity over TX may try to grow into a few convective
clusters, and rainfall rates should be intense enough for a
localized flash flood risk. However it appears like the better
threat for more widespread organized development is over northern OK
into central KS, closer to the dryline/warm front intersection. This
activity will have greater lower level convergence to work with and
also be closer to the mid level vort energy swinging through the
High Plains. This activity should grow upscale Sunday evening into
the overnight, potentially into an MCS, at which point it should
feel the impact of the strong southwesterly low level jet and begin
turning easterly and then southeasterly aligned with the upwind
Corfidi Vectors and along the instability gradient. As this process
occurs some training/backbuilding on the southwest extent is
probable resulting in a scattered flash flood threat.

The exact MCS location/track remains a bit uncertain. As already
mentioned, the HREF members are all over the place, and thus the 00z
HREF probabilities do not appear all that useful. Best guess at this
point is something close to the 00z GEM reg might be reasonable.
Also like the placement of the 00z AIFS and EC mean...with a
maximum QPF somewhere from northeast OK into southeast KS,
southwest MO and northwest AR. Do consider these areas to be a
higher end Slight risk today, as where any training MCS does
develop we could be looking at a swath of upwards of 3-5" of rain.
Main thing to watch will be how far north the warm front gets today
over OK/KS and where convection first starts to grow upscale. If
this all happens earlier/farther south then OK into northern AR
become more in play for flash flooding...while if it happens later
and farther north then we are looking more at eastern KS into
central MO. Tend to think both the 00z and 06z HRRR are too far
north, but also can not completely rule that scenario out either.

Another area of interest will be farther northwest into central and
western NE, closer to the low track. A multi-model signal exists for
a second QPF max over this area...which makes sense given what
should be impressive synoptic driven ascent and instability along
the stationary/occluded front. Considered expanding the Slight risk
into this area...but opted against that for now. This area remains
in severe drought and possible that a majority of the training
convection ends up over the high FFG sand hills. These factors
should keep the flash flooding localized in nature, and thus will
maintain the Marginal.

The extension of the Marginal risk into Southeast accounts for
organized convection that should be ongoing this morning, and then
potential isolated redevelopment later today near the lingering
boundary where substantial instability will support heavy rainfall
with any storms that are able to develop.

...Northeast...

A Marginal risk continues over portions of northern New England on
Sunday as a deep layered low remains overhead. Instability and PWs
are lower today, however cold air aloft and some surface heating
should allow for showers and a few heavier convective cells to
develop this afternoon. Both the 00z HREF and 18z REFS indicates a
30-40% chance of exceeding 1" of rain in an hour, and cells will be
slow moving.

Chenard


Day 2
Valid 12Z Mon May 19 2025 - 12Z Tue May 20 2025

...THERE IS SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE
CENTRAL PLAINS INTO THE LOWER AND MIDDLE MISSISSIPPI VALLEY...

Another day of widespread heavy rainfall expected across the middle
portion of the country on Monday as the longwave trough and embedded
shortwave energy slowly moves eastward. It will likely be an active
day/night with a broad region where flash flooding will be possible.
Not much change was needed to the inherited risk area, with a Slight
risk stretching from northeast TX into southern IA. Expect
convection to again develop Monday afternoon along the dryline and
approaching cold front from TX into NE. The northern extent of the
Slight risk will be near the warm/stationary front extending east
across northern MO and southern IA. Strong forcing overrunning this
boundary will likely result in an expansive area of convection, with
some training/backbuilding possible. The southern portion of the
Slight risk from TX into eastern OK and AR covers initial dryline
development and possible upscale growth. While the low pressure
driven stronger convergence will be farther north over IA/MO, there
are indications that a corridor of enhanced low level moisture
transport could evolve from TX into AR aided by shortwave energy at
the base of the longwave trough. Several pieces of guidance thus
depict a secondary max QPF swath over these areas from possible
training convection.

Exactly where the focus of highest QPF ends up remains a bit of a
question, but generally anywhere within the Slight risk is in play.
There are meteorological reasons (described above) for two maximum
rainfall swaths, one farther north near the warm front over northern
MO and southern IA, and another from northeast TX into AR. However
getting these details right at this lead time is difficult. So
whether or not we end up seeing two separate areas of training
convection or one more consolidated area, the main story is that
the ingredients will be in place for training/backbuilding
convection leading to excessive rainfall. Some of these areas will
also likely see heavy rain on day 1 as well, and so hydrologic
conditions could be more sensitive by this day 2 time frame. Thus
do consider most of the Slight area as a higher end Slight risk at
this time, and think areas of flash flooding are likely. It seems
possible (maybe even probable) that an embedded MDT risk will
eventually be needed somewhere within the broad Slight area.
However uncertainty in both the convective details and hydrologic
conditions (pending what rainfall happens on day 1) leads to low
confidence in any MDT risk location at this time. Thus we will hold
with a higher end Slight and continue to monitor trends.

Chenard


Day 3
Valid 12Z Tue May 20 2025 - 12Z Wed May 21 2025

The system described in the day 1 and 2 discussions begins moving
east on Tuesday. The overall setup for heavy rainfall amounts is
generally not as good by this time as it was on previous days
farther west. The large scale forcing is more progressive by Tuesday
and the degree of instability is not as robust. Thus not surprising
that the global model QPFs are generally lower than what is forecast
farther west on day 2. With that said, there is likely still an
excessive rainfall risk Tuesday. While the system is becoming more
progressive by this time, there will be a stationary front extending
from IL into KY through, with enough moisture transport and synoptic
ascent to support a broad area of convection along this front. This
setup thus could allow for either multiple convective rounds near
the front, or even a more prolonged period of repeat/training
convection. The main question will be whether we are able to
maintain enough instability to support prolonged intense convection
and also whether the mid/upper level forcing is enough to allow for
a persistence of stronger convection. It is also worth noting that
portions of KY and WV are more sensitive to additional rain, with
higher soil saturation and streamflows in place.

Overall think this is a solid Slight risk, with isolated to
scattered flash flooding possible anywhere from IA to
KY/TN/WV...generally along and just south of wherever the
stationary/warm front ends up by this time. The potential for
greater flash flood coverage and higher impacts is
uncertain...noting the aforementioned uncertainties with
forcing/instability and the general downtick in model QPFs by this
time. However the orientation of the forcing and stationary front
does suggest a potential for training and more significant rainfall
totals, which could open the door for a corridor of more widespread
and/or higher impacts. The 00z RRFS depicts a swath of strong
convection Tuesday, but generally shows things progressive, keeping
most areas in the 1-2" range...likely not enough for widespread
flash flooding. However it does show some swaths over 3", especially
over portions of KY and TN where a bit more training occurs. So we
will continue to monitor trends, and pay close attention to areas
that may be more sensitive to additional rainfall, such as KY and WV.

Chenard

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