FOUS11 KWBC 160846
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
346 AM EST Sun Feb 16 2025

Valid 12Z Sun Feb 16 2025 - 12Z Wed Feb 19 2025

...Great Lakes/Northeast... Days 1-3...

A powerful multi-hazard winter storm will continue to push 
into/through the Northeast today as the sharpening shortwave 
beneath the 160kt jet exits the Midwest. Cold air over the 
Northeast will eventually be scoured out nearly up to the Canadian 
border as low pressure lifts from near PIT this morning to central 
NYS this afternoon. By then, a new area of low pressure over Cape 
Cod will start to become the dominant low and lift into the Gulf of
Maine as the old parent low weakens into western New England. The 
new low will then move into Atlantic Canada tonight. The evolution 
will favor all snow near the Canadian border and into interior 
Maine where it will stay coldest thanks to the transfer of energy 
to the coast, a transient mixed area of sleet/freezing rain to the 
south, and rain surging northward after starting as snow this 
morning farther south. Icing will hang on longer in the colder 
terrain areas like the Adirondacks, Catskills, Berkshires/Greens, 
and Worcester Hills/Monadnocks but also across coastal Maine on the
north side of the new area of low pressure. The low pressure 
center will continue to deepen as it pulls away tonight into the 
low 970s mb and the synoptic snow will end Monday morning. 

WPC probabilities for at least 6 inches of snow today are highest 
north of I-90 in NY, north of the MA/VT/NH border, and 
north/northwest of I-95 through Maine. Totals near the Canadian 
border and over northern Maine may eclipse a foot (probs 30-70%+). 
Between the coast and I-90 or so, ice will be the main problem 
before some areas change over, briefly, to a cold rain (esp the 
valleys via strong southerly flow). WPC probabilities for at least 
0.25" icing are highest (40-70%) in the Berkshires/southern Greens 
and into the Worcester Hills/Monadnocks.

On the backside of the system, colder air will rush in across the 
Great Lakes and into the central Appalachians, supporting lake 
effect snow and upslope snow, respectively. Over eastern WV into 
the MD Panhandle and the Laurel Highlands, upslope will provide for
modest snow totals with WPC probabilities of at least 4 inches 
>70%. Though that area will see snow ending on Monday, the lake 
effect machine will keep cranking for the next few days as an upper
low swings through the region out of Canada. The flow will back 
from NW to WNW and favor the typical lake belts, but especially 
over the eastern U.P. of Michigan and southeast of Lake Ontario. 
There, WPC probabilities for at least 8 inches of snow over the 
next few days are high (>70%) and are moderate (40-70%) for 18 
inches of snow in localized areas that remain under banding. 

...Pacific Northwest/Rockies/Northern High Plains... Days 1-3...

An active Pacific jet will guide a lead system into the Northwest 
today, followed by onshore flow into Monday, then another system by
Tuesday into Wednesday. Snow levels will be a bit below pass level
and waver there for the next couple of days. East of the Divide a 
very cold air mass will be in place thanks to high pressure over 
Canada that pushes southward through the Plains, setting up upslope
flow into western MT. For the first system, Sun-Mon (though into 
Tue over WY), the highest snow totals will be over the Cascades 
eastward into the central Idaho ranges, western MT/WY and into 
northern CO/southern WY. Several feet of snow are likely in the 
higher terrain with only a brief break between systems. IVT values 
exceeding the 90th percentile will move through the region today, 
but then drop after tonight as the jet flattens out a bit. 
Nevertheless, the nearly continuous terrain-enhanced snow will 
accumulate well over 1-2 ft with WPC probs > 70% in the mountains. 
Snow will be fairly heavy over western-central MT on the upslope 
side as well, where WPC probs for at least 8 inches of snow are 
>50% around Billings up to Great Falls. 

The next system will enter the PacNW D3 (Tues afternoon) with some
light snow for the Cascades. This will push eastward into D4.

...Central Plains/Mid-MS Valley/Mid-South... Days 1-3...

Eastward extension of the Western US moisture will reach the 
central Plains later this evening as WNW flow rushes through the 
region. 700mb WAA will help drive light to modest snow across the 
Black Hills southeastward into Nebraska overnight with fairly high 
SLRs >15:1. Light snow will extend farther into northern MO by 
early Monday before tapering off thereafter as the pattern shifts a
bit. WPC probabilities for at least 4 inches of snow D1-1.5 are 
30-80% in this NW to SE stripe but diminish to <30% over northern MO.

Overnight Mon into Tue, height falls will dig through the Four 
Corners with a multi-stream jet east of 100W. A strong Arctic front
will push southward and increase low-level convergence, helping to
drive an expansion of snow through KS and into northern OK and 
eastward, growing heavier as the shortwave aloft reaches the Plains
Tues evening. Heavy snow is expected to develop over eastern KS 
into western MO beneath a quickening upper jet east of the 
Mississippi, bleeding southward into northern/northeastern OK and 
northern AR overnight. By the end of the period, the shortwave will
continue into the Mid-South with light to moderate snow into TN. 
On the southern side of the precip shield, colder air at the 
surface will undercut the milder >0C thermals aloft over central AR
where freezing rain is likely to form (with some sleet to the north).

WPC probabilities for at least 4 inches of snow are >50% from 
northwestern KS eastward to southern IL/western KY/northwestern TN,
including northern OK/AR. Within this broad region, an axis of 
heavier snow is likely to develop with rates >1"/hr and snow totals
>8". WPC probabilities for at least 8" are >50% over southeastern 
KS and southern MO. Farther south, ice probs for at least 0.10" are
>30% around the Ouachita Mountains. 

Fracasso

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

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

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

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