FOUS11 KWBC 150731
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
231 AM EST Wed Jan 15 2025

Valid 12Z Wed Jan 15 2025 - 12Z Sat Jan 18 2025

...Great Lakes & Central Appalachians... 
Days 1-2...

Ongoing lake-effect snow over the eastern Great Lakes will wind 
down today as a new shortwave moves in from the northwest, bringing
light snow to the Upper Midwest/Western Great Lakes on WAA. As the
warm front passes, winds will switch to NW as the cold front makes
its approach but weakens across the region in response to height 
rises from the west. Regardless, some lake enhancement or lake 
effect snow is likely over much of the region but with overall 
light amounts over the U.P. and into western Lower Michigan. 

East of Lakes Erie and Ontario, system will bring in some light 
snow followed by a period of lake enhanced/effect snow D2 before 
ending D3. To the south, shortwave will swing right through the 
central Appalachians, maximizing upslope into eastern WV where 
several inches of snow are likely D2. WPC probabilities for at 
least 6 inches are high (>70%) especially over 2000ft. 


...Northern/central Rockies/High Plains...
Day 3...

As an upper ridge builds across the Northeastern Pacific Thursday 
into Friday, downstream response will be digging troughing out of 
western Canada nearly due south through the High Plains via a 
strong cold front ("blue norther". Though moisture will be 
limited, strong northerly flow will support upslope enhancement 
into some of the terrain over central/western Montana (esp the 
Little Belts and Big Snowy Mountains) southward into the Bighorns, 
Absarokas, and into the southeastern WY ranges. 

As the front dives southward, steeper lapse rates will support 
snow squalls along the front Friday in Montana progressing into 
Wyoming. Snow squall parameter per the guidance still shows values 
>1 (and even >3) suggesting the possibility of bursts of snow with 
sharply reduced visibility leading to near whiteout conditions. CAM
guidance should shed a little more light on the threat over the 
next two days, but we have outlined this area in our Key Messages 
(see below). WPC probabilities for at least 4 inches of snow over
Montana/Wyoming are moderate (40-70%) and mostly over the terrain 
with light snow (1-2" elsewhere. 

As the system races southward, cold front will slow a bit across 
the Rockies but continue to plunge through the High Plains, 
favoring upslope enhancement into the Front Range late Fri/early 
Sat. Snow will expand through the I-25 corridor into the Denver 
Metro area with higher amounts across the Front Range as 
temperatures fall into the teens, helping to increase SLRs from 
~12:1 up toward ~18:1. Additional snowfall is likely past 12Z Sat. 
Through then, WPC probabilities for at least 4 inches of snow are 
at least 50% across the Front Range.


For the Day 1-3 period, the probability of significant icing of at
least 0.10" is less than 10 percent across the CONUS.


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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