FOUS30 KWBC 160730
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
330 AM EDT Mon Mar 16 2026
Day 1
Valid 12Z Mon Mar 16 2026 - 12Z Tue Mar 17 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE MID-ATLANTIC AND NORTHEASTERN U.S...
Broad axis of diffluence positioned over the Ohio Valley into the
Northeast will lead to multiple rounds of convection once east of
the Appalachian front. Warm moist air will continue to funnel
poleward ahead of a very amplified trough axis centered over the
Midwest to Mid-Mississippi Valley. PWATs across the Mid Atlantic
have already surged beyond 1", a solid 3 standard deviations above
normal compared to climatology putting into the 97-99th percentile
for mid-March. Expectation is for this surge to continue pushing
further north within the amplified flow east of the Mississippi
leading to a large swath of the east coast to exhibit an
environment favorable for at least the threat of heavy rainfall.
A multi-round scenario of convective impacts are anticipated as
weak mid-level perturbations usher north-northeast ahead of the
mean trough and cold front migrating through the Ohio Valley. Prior
to the cold front arrival and associated precip field along and
ahead of the front, moderate to locally heavy rains from
convective clusters could help prime local soils before the main
time frame of impact after 18z occurs. One of the trends within
guidance was a relatively skinny convective segment that will be
the main player in the higher rates exhibited in this setup. The
linear segment will be relatively progressive, but rates between
0.75-1.5"/hr at peak intensity are plausible as it moves through
the Mid Atlantic and Northeast leading to a threat for flash
flooding as it migrates into the Piedmont and urban zones
characterized within the Northeastern Megalopolis. Areal average
of 0.75-1.5" is forecast for much of the area from northern VA up
into NY state and Northeast New England. The maxima of over 2" is
still showing up within deterministic output via both global and
CAMs physics. The area of interest continues to point to
CT/RI/Southern MA as the primary spot for more appreciable totals
2". This is supported via the neighborhood prob fields of 50-80%
for at least 2" by the latest 00 HREF output. Other notable areas
include high probs >70% for at least 1" aligned along the Blue
Ridge to the I-95 corridor for VA/MD/PA extending into the Lower
Hudson and Catskills area of NY state. Another axis of higher probs
exists across eastern ME and parts of Northern New England which
coupled with high SWE presence should allow for rapid snow melt and
potential for local hydrologic issues stemming from both the
precip and snow/ice melt. This signal was sufficient for
maintenance of the previous MRGL risk with only some minor
adjustments on the southern edge of the risk area to account for
the latest model trends.
The progressive nature of the precip should curb some of the flash
flood concerns making this a solid MRGL risk with perhaps a bump in
the risk magnitude if guidances trends more aggressive in QPF
output. For now, this is a classic setup for early spring
convection and modest flash flood prospects.
Kleebauer
Day 2
Valid 12Z Tue Mar 17 2026 - 12Z Wed Mar 18 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
WASHINGTON STATE...
Active pattern across the Gulf of Alaska will lead to another AR
contribution into portions of the Pacific Northwest as the main
IVT surge will adjust south into WA state after impacting
neighboring British Columbia the day prior. Looking at IVT values
between 500-700 kg/ms across northwest WA state with the surge
propagating far enough inland to impact the Northern Cascades.
Rainfall amounts between 2-3" will be common in the hardest hit
areas, mainly into the Olympic Peninsula, Chehalis River valley,
as well as the Cascades to the east of Seattle. Rates will lack
vigor to the point for a more substantial impact, so the threat is
mainly due to prolonged moderate to locally heavy rain prospects
falling over relatively moist soil layer present after being
impacted for weeks leading in. The previous MRGL risk was generally
unchanged with the threat leaning towards the lower-end of the risk
threshold. Areal hydrologic concerns are still viable with river
and small stream flooding the most notable potential impacts.
Kleebauer
Day 3
Valid 12Z Wed Mar 18 2026 - 12Z Thu Mar 19 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
WASHINGTON STATE...
Occluded low over the Gulf of Alaska a strong mid-level ridge
positioned across the Southwest U.S. will lead to a continued
transport of modest IVT into WA state for the D3 period. AR
dominated pattern will enhance rainfall prospects for the northern
half of WA leading to cumulative rainfall totals breaching 4" in
spots within the Northern Cascades, Olympics, and adjacent coastal
areas of northwest WA. Real concern is the growing hydrologic
factors with river flooding coupled with moderate rainfall posing a
problem for areas around the main rivers and tributaries for the
aforementioned areas. Flash flood threat remains low due to the
rates anticipated with the rainfall as hourly rainfall will remain
<0.5"/hr for a majority of Wednesday. However, the coupling of the
previous days rain and the already saturated soils will likely lead
to some hydro concerns mid-week, so maintained the previous MRGL
risk inherited with only some minor tweaks at the southwest edge of the risk.
Kleebauer
$$
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