FOUS11 KWBC 150803
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
303 AM EST Sat Feb 15 2025

Valid 12Z Sat Feb 15 2025 - 12Z Tue Feb 18 2025

...Rockies... Day 1...

The upper trough centered across the Four Corners will continue 
eastward today, with the last trailing vorticity pushing through 
the CO Rockies this afternoon. Light to modest snow over the higher
peaks of CO into southeastern WY will diminsh through the day with
an additional 4-8+" likely and much lighter snow into the valleys 
and Front Range. 

...Corn Belt/Midwest/Great Lakes/Northeast... Days 1-3...

Trough in the Rockies will exit today with a long extension to the
northeast into the Upper Midwest. Base of the trough will lag 
through TX but additional height falls out of Canada will slow the 
northern stream, alloiwing the trough to recongeal as it heads into
the Ohio Valley and then the Northeast. The setup will be broad 
WAA-driven snow into the Great Lakes and Northeast but as the 
trough sharpens and jet becomes more S-shaped along 80W, low 
pressure will deepen and surge mild air far northward toward the 
Canadian border, allowing snow to change to sleet/freezing rain and
just rain through Sunday with the main low into western NY. By 
that time, a new area of low pressure will start to take shape and 
eventually take over southeast MA into the Gulf of Maine, 
essentially halting the northward surge in milder air into/through 
New England as the low finall then lifts northeastward along the 
Maine coast and into Atlantic Canada by early Monday. 

For D1, strengthening jet across Michigan into Canada will act to 
maintain snowfall over Lower MI today where WPC probabilities for 
at least 4 inches of snow are >50% for the central/eastern 2/3rds. 
Into the Northeast, WAA-driven snow will overspread the region this
morning/afternoon where temperatures are cold. Could capitalize on
good WAA for this front-end thump of snow but strong southerly 
surge will drive the mixed ptype zone northward from the Mid- 
Atlantic later this afternoon into tonight. WPC probs for at least 
4 inches of snow are highest (>50%) farthest north where the cold 
air will hang on the longest -- north of I-90 into the Adirondacks 
and Green Mountains as well as into the Berkshires and Worcester 
Hills. To the south, temperatures are sub-freezing thanks to high 
pressure overhead this morning but aloft it is near and just above 
0C. Any snow will turn to sleet or more likely freezing rain from 
across the Midwest and especially into the central Appalachians (SW
VA into central PA then up into the Southern Tier of NY). Ice 
accumulation will depend on how long the cold surface temperature 
can resist the strong surge in mild air from the south. WPC probs 
for at least 0.25" icing are at least 30% along the WV/VA line 
northward to the I-99/US 220 corridor. 

Into D2, low pressure over southeastern OH will track 
northeastward toward western/central NY by the afternoon as the 
coastal low takes shape, which should stop the northward push of 
the mix ptype zone but not before it may reach all the way to the 
Canadian border (NY/VT) and into Downeast Maine. The remaining cold
air will be largely confined to northern Maine where WPC probs for
at least 6 inches of snow are >50% north of I-95. Ice 
accumulations will be primarily over eastern NY and north of I-95 
into New England, especially into the Berkshires and Monadnocks 
where ice probs for at least 0.25" are at least 20%. 

By D3, storm will be well out into the Atlantic but with a broad 
cyclonic flow back across the Great Lakes, supporting lake-effect 
snow off all the lakes but especially off Lake Ontario on WNW flow.
This could support a healthy single band into the northern SYR 
suburbs from Oswego toward Rome/Utica where at least several inches
of snow are possible. 

...Pacific Northwest/Rockies/Central Plains... Days 1-3...

The next multi-vorticity lobe upper low in the northeast Pacific 
will send a cold front into the Pac NW later today with snow levels
around 3000-4000ft for the WA/OR Cascades. With the upper jet 
nosed into southern OR for the next two days or so, onshore flow 
will continue to provide Pacific moisture to the region and into 
the Great Basin/northern Rockies, overriding cold air on the east 
side of the Divide. There, lower level convergence should enhance 
snowfall over western MT D2 into D3 with two-day WPC snow 
probabilities for >12" >70%. Snow into the Cascades will affect 
the passes esp D1-2 until the trailing upper low finally reaches the coast.

Farther southeast, moisture will spread back into the central/CO 
Rockies with additional amounts of at least 6 inches likely by D3. 
Onto the Plains, incoming vort maxes in the quick WNW flow atop 
lower-level WAA will favor light snow stretching from western NE 
southeastward toward the MS River Valley including much of KS. The 
air mass will be fairly cold thanks to high pressure starting to 
assert itself across southern Canada into the Dakotas, supporting 
SLRs ~15:1. Through 12Z Tue, WPC probabilities for at least 4 
inches of snow are 40-60% over the northern half of KS into 
southern NE with more to follow. 

Fracasso

...Winter Storm Key Messages are in effect. Please see current 
 Key Messages below...

https://www.wpc.ncep.noaa.gov/key_messages/La...

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