FOUS11 KWBC 140845
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
345 AM EST Fri Feb 14 2025

Valid 12Z Fri Feb 14 2025 - 12Z Mon Feb 17 2025

...Central NYS... 
Day 1...

WNW flow will continue a lake effect snow band off Lake Ontario 
into the Syracuse metro this morning/afternoon and diminish later 
this evening as it lifts northward. Day 1 snow probs for >4" are 
40-90% in a narrow corridor.

...Sierra Nevada through the Rockies... 
Days 1-2...

Atmospheric River has moved well inland, but the lagging upper 
trough will continue onshore flow with instability enhancing precip
over the Sierra Nevada as the low opens into a slow-moving trough.
Snow levels have fallen back to 5000-6000ft under the trough axis 
(Sierra) and around 4500ft (Shasta/Trinity) bringing light snow to 
lower elevations. Snow should taper off later this evening from 
west to east across CA. Day 1 snow probs for an additional 8" are
moderate(40-70%) across much of the Sierra.

Moisture has reached the Rockies with a strong influx from the SW 
and the trough axis will pass the Four Corners early Sat, favoring 
moderate to heavy mountain snow with gradually lowering snow levels
as colder air moves in. Snow rates will ease over the next 12-24 
hours with additional snow over the Wasatch and Tushar in Utah and 
western CO Rockies northward into the Tetons and eastward into the 
San Juans and Sangre de Cristos. 48-hr snow probs for >12" are 
over 80% for these areas.

...Pacific Northwest...
Days 2-3...

The next multi-vorticity lobe upper low in the northeast Pacific 
will send a cold front into the Pac NW late Sat into early Sun. 
Snow levels around 3000-4000ft for the northern-southern Cascades
(respectively) will give light to moderate snow to the passes that 
continue into early Monday as the trailing main upper low finally 
reaches the coast. WSW flow will spread moisture across eastern OR 
into ID, western MT and western WY where the favored terrain will 
see moderate snow totals. Cold temperatures over the northern Great
Basin/northern Rockies will favor at least some snow to most 
valley floors. 48-hr snow probs for >12" are >50% for this higher terrain.

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

Eastward extension of the western trough will bring WSW flow to 
the Upper Midwest later today with embedded vort maxes atop an 
inverted surface trough. Thump of snow with this inverted trough is
on warm air advection, but sufficient cold air is there to allow 
heavier snow with >10:1 SLRs over much of WI tonight. WPC snow 
probs for >4" are >50% from southeastern MN across central WI. A 
broader area of light snow is expected over much of the region, 
setting up a somewhat prolonged but interrupted period of light snow.

Into D2, the western trough will push into the Plains and start to
amplify in concert with the downstream upper jet (>160kts) across 
the Great Lakes. Moisture will continue to spread eastward across 
Lower Michigan, southern Ontario, then into the Northeast. With a 
trend toward a slower/sharper upper system, QPF has increased over 
much of the Midwest and into Lower Michigan where WPC probs for at 
least 4 inches of snow on Sat are >50% over most of Lower Michigan,
but are at least 25% from southern Iowa and across northern IL. On
the eastern side, WAA will promote light snow over much of NY with
WPC probs for >4" snow highest over the Poconos into the 
Catskills, but also at least 30% over the higher elevations above 
1500ft or so. To the south, cold air at the surface along/east of 
the Appalachians (NC through VA into central PA) will hang tough as
overriding precip from the west encroaches, favoring freezing rain
and perhaps some sleet on Saturday. With a sfc low track from the 
Mid-South through OH, warm air will eventually win out due to 
strong 50kt SW 850 flow. WPC probs for at least 0.10" icing are 
>50% over southwestern VA northward into central PA, where there 
are also probs for >0.25" icing (30-50%). 

By D3, the surface low is forecast to track from just west of PIT 
toward western/central NY with some coastal redevelopment over 
southeastern MA (Cape Cod) that may move into the Gulf of Maine. A 
lot of details have yet to be resolved, but this scenario will 
likely result in all snow close to the Canadian border where warm 
air intrusion is least likely, a mix of snow to sleet/freezing rain
over much of the area between the I-90 and I-80 corridors, and 
rain farther south and southeast as warmer air surges up the coast.
The timing of the many players will modulate the amount of each 
ptype, but for now the highest probabilities for at least 8 inches 
of snow are over the Adirondacks into northern VT/NH and interior 
Maine. Several inches of snow are probable (40-60% chance) along ad
north of the I-86/Rt 17 to I-84 corridor (NY to CT). Icing is most
likely in areas that are able to stay coldest the longest, 
including central PA, the Poconos, Catskills, and Berkshires where 
WPC probs for at least 0.10" icing are >50%. Again, the details of 
the system are still in flux which will influence where and as what
type the precipitation may fall. 

Fracasso

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

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

$$
--- SBBSecho 3.20-Linux
 * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (618:250/1)