FOUS11 KWBC 050629
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
129 AM EST Thu Dec 5 2024

Valid 12Z Thu Dec 05 2024 - 12Z Sun Dec 08 2024

...Eastern Great Lakes and Northeast... 
Days 1-3... 

Strong low pressure moving through Quebec this morning will 
continue eastward, with WAA-driven snow over northern New England. 
500mb heights/wind are near the CFSR reanalysis min/max 
(respectively) with this potent system. The associated cold front, 
responsible for numerous snow squalls yesterday afternoon and 
overnight, will help feed moisture into northern/interior Maine 
where sub-freezing temperatures will support all snow this morning.
Low pressure will quickly translate into Atlantic Canada early 
this afternoon, with the FROPA turning winds around to the 
northwest and helping to enhance orographic lift across much of the
Northeast into the central Appalachians. Strong pressure gradient 
will also maintain windy conditions with blowing/drifting snow over
the interior and near-blizzard/blizzard conditions in the higher 
elevations (esp WV). Lake-effect snow, already in progress over MI,
will redevelop/strengthen over the eastern Great Lakes by this 
afternoon on NW flow with some double (Lake) dip increase in 
moisture. CAM guidance continues to depict some rather robust 
single bands off some of the lakes with a far reach inland of at 
least lighter snow. Winds will eventually back and lighten by 
tomorrow with less coverage/intensity overall but still some more 
potent bands possible. A trailing shortwave out of Canada will 
swing through the Lakes late Friday, again enhancing some lake- 
effect snows across MI into NY and NW PA. 

WPC probabilities for at least 12 inches of additional snow after 
12Z Thu are highest (>50%) east of Lake Erie (NW PA into SW NY) and
southeast of Lake Ontario (between ART and SYR). Moderate snow 
(>8" is likely over the higher terrain of the Adirondacks into the
Green and White Mountains due to upslope flow. In addition, the 
eastern U.P. of Michigan and the western side of Lower Michigan 
show moderate (40-70%) and low (10-40%) probabilities, 
respectively, of at least another 8 inches of snow through 
Saturday. 

Lastly, with the progression of the cold front this morning, the 
threat of snow squalls remains for parts of the northern Mid- 
Atlantic into New England. This may produce a quick drop in 
visibility coincident with gusty winds and slippery travel. 


...Pacific Northwest/Northern Rockies... 
Day 3...

Upper low in the northeastern Pacific will stream eastward along 
50N into British Columbia, bringing in a surge of moisture to the 
Cascades then into the northern Rockies on Saturday. Snow levels 
will be on the higher side, about 8000ft at precip onset, but will 
lower to around 5000-6000ft Saturday afternoon as the front moves 
in, and falling farther to around 3500ft as the precipitation 
lightens into Sunday morning. Snow will likely affect the higher 
passes, where the probability of at least 6 inches is >50% above 
4000ft or so. East of the Cascades, some icing and/or a wintry mix 
of sleet/freezing rain will be possible as colder surface 
temperatures are overrun by mild air aloft. Into the northern 
Rockies, moisture will get wrung out over the higher terrain with 
several inches likely (>50% chance of 6 inches) on the higher 
mountain ridges. 


The probability of significant ice >0.25" across the CONUS is less
than 10 percent. 


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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