Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
213 PM EST Mon Jan 10 2022

Valid 00Z Tue Jan 11 2022 - 00Z Fri Jan 14 2022

...Great Lakes...
Days 1-3...

Secondary cold surge associated with a shortwave digging across
Northern New England will shift winds more to the north and
continue CAA across the still warm Great Lakes. With flow more
northerly than westerly, the fetch length decreases, so while LES
is likely to continue D1, it should consist more of weaker
multi-bands than what occurred on Sun/Mon. WPC probabilities on D1
for more than 4 inches are moderate near the Chautauqua Ridge SE
of Lake Erie, and around the Syracuse/Finger Lakes region SE of
Lake Ontario. This LES should wane and dissipate Tuesday aftn as
dry air envelops the area and is replaced by shortwave ridging.
However, late D2, and especially on D3, another cold front will
drop across the Great Lakes followed by pronounced eastern
troughing and renewed CAA. This should redevelop LES, especially
across the eastern U.P. of MI. However, favorable conditions for
LES are likely to be transient with this next front, and this is
reflected by WPC probabilities for more than 4 inches that are 5
percent or less. LES may develop downstream of Lake Erie and
Ontario late D3, but accumulations before the end of the forecast
period are expected to be light.


...Pacific Northwest into Northern Rockies...
Days 1-3...

A series of shortwaves split by quick shortwave ridging will bring
periods of precipitation to the Pacific Northwest this week. The
lead shortwave will move onshore tonight followed by zonal but
moist flow, with a more pronounced shortwave lifting into WA state
Thursday morning /D3./ Both of these features will help transport
moisture onshore, with ascent through height falls and leading
mid-level divergence producing precipitation, generally from
northern OR through WA and into the Northern Rockies of ID/MT.
Snow levels are progged to climb from 4000 ft tonight to as high
as 8000 ft in the most robust moisture plume Thursday, confining
the heavy snow above the mountain passes. WPC probabilities for 6+
inches are low to moderate each day, focused in the WA Cascades,
but at times spilling over into the Northern Rockies.

At the same time, periods of light precipitation spilling over the
Cascade crest and into the Columbia Basin will fall over cold
surface temperatures as a surface high pressure only slowly
retreats through D2. This could allow for light freezing rain
accumulations, and WPC probabilities are as high as 20-30%,
peaking on D2.


Weiss