FOUS11 KWBC 190701
QPFHSD
Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
201 AM EST Wed Feb 19 2025
Valid 12Z Wed Feb 19 2025 - 12Z Sat Feb 22 2025
...Southern Mid-Atlantic States... Day 1...
A significant winter storm will continue to spread eastward into
the southern Mid-Atlantic with potentially major impacts including
heavy snow and significant ice. See the latest Key Messages linked
at the end of the discussion.
Surface low along the Central Gulf coast will cross North Florida
early this afternoon and parallel the Southeast Coast tonight. The
northern stream shortwave responsible for the heavy snow in the
Plains will continue eastward into the southern Mid-Atlantic,
helping to spread generally light snow to the southern
Appalachians, aided by some orographic enhancement. WPC
probabilities for at least 4 inches are generally <30%.
As the Gulf low transitions to a western Atlantic/coastal low,
precipitation will progress to the VA/NC coast with snow to the
north (solidly cold column over VA) and freezing rain and sleet to
the south where warmer air aloft will overrun the cold surface
temperatures near and just below freezing over eastern NC and into
portions of eastern SC as well. Snowfall to the north will likely
maximize later this afternoon and evening as the surface low starts
to deepen over the Gulf Stream, with locally heavier rates >1"/hr
over southeastern VA, leading to moderate/heavy amounts. WPC
probabilities for at least 6 inches of snow are >50% there. There
is a much larger footprint of >2" probabilities of at least 40%,
extending from southwestern VA eastward, as far north as
Fredericksburg, VA to Rehoboth Beach, DE, and as far south as the Raleigh-Durham metro.
Into NC, several hours of freezing rain are likely starting this
afternoon and continuing into the evening. Accretion will depend on
rainfall rates (which limit accretion), wind, and time of day, but
most of the guidance still indicates the potential for a couple
tenths of an inch of ice, roughly along and east of I-95 in eastern
NC. WPC probabilities for at least 0.10" ice are >40% with some
areas likely seeing >0.25" ice. Precipitation will wind down
overnight and end by Thursday morning.
...Great Lakes/Northeast... Days 1-2...
Lake effect snow will diminish this morning as height falls over
the Corn Belt move into the region, favoring widespread light snow
over the Great Lakes and Midwest tonight into Thursday. WPC
probabilities for at least 4 inches of snow are low (<40%) except
for some lingering lake bands and/or lake enhanced snows.
...Pacific Northwest through the Central Rockies... Days 1-3...
A potent but progressive Pacific system will start to move into
the Northwest this morning, spanning the latitudes from NorCal up
to the Canadian border. IVT will be modestly high (~90th
percentile) into NorCal/southern OR/northern NV toward Idaho,
supporting light to moderate snows for the terrain with snow levels
near 3000ft to the north and 5000ft to the south that will rise a
bit as the core of the moisture plume pushes through. The system
will move steadily along which will end QPF from west to east
starting as early as tonight over the Cascades and on Thursday over
the Great Basin. Moisture will wane with decreasing synoptic
support into Thursday, with snow confined mainly to the Unitas and
higher CO Rockies by then. For the 2-day period, WPC probabilities
for at least 8 inches of snow are highest (>70%) over the higher
terrain above 6000ft closer to the coast, 7000-8000ft over the
Great Basin, and 9000ft over CO/WY. A new system will to enter the
Northwest by D3 with lighter snow into the northern Cascades.
...Southeastern Mass... Day 2...
The exiting system from the Southeast/southern Mid-Atlantic will
track northeastward and may clip southeastern MA/Cape Cod on
Thursday on its way into Atlantic Canada. The question revolves
around the speed of the incoming northern stream upper low and how
much it can capture the exiting system and pump up the downstream
ridge. 00Z guidance still shows at least some snow into the region,
but vary on how much. The best chances for snowfall over 4 inches
remains over Nantucket (~70%) as well as both Martha's Vineyard and
Cape Cod (40-60%), with low probs (10-20%) from Block Island to
New Bedford to Plymouth.
Fracasso
...Winter Storm Key Messages are in effect. Please see current
Key Messages below...
https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_2.png
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