Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
235 AM EST Wed Jan 24 2024

Valid 12Z Wed Jan 24 2024 - 12Z Sat Jan 27 2024

...Western U.S....
Days 1-3...
A closed low will continue to move east across the northeastern
Pacific toward southern British Columbia and the Pacific Northwest
today.  Precipitation will return to the Pacific Northwest and
Northern California along with a weakening occluded front moving
into the region this morning.  This will bring a brief period of
moderate to heavy high elevation snow to the region this morning,
followed by additional light snow that will supported by onshore
flow in the wake of the leading frontal band.  Some locally heavy
snow accumulations are expected in the Cascades, mostly for areas
above 4000 ft.

The upper low is expected to transition to an open wave as it
moves inland on Thursday.  Remnant energy associated with this
system is forecast to dig southeast, carving out a deep trough
over the Four Corners region Thursday night.  This will bring
areas of snow across the Intermountain West into the Four Corners
region, with some locally heavy accumulations possible, especially
along the Utah and southwestern Colorado ranges.  Meanwhile,
additional energy moving off of the top of a building ridge will
help generate additional heavy accumulations over the Washington
Cascades where snow levels are expected to linger around 4000 ft
on Thursday.  By Friday snow levels will begin to increase notably
as an amplified shortwave ridge shifts east from the eastern
Pacific into the western U.S.


...Upper Midwest to the Northeast...
Days 1-3...
A strong upper ridge extending from the western Atlantic into the
eastern U.S. will direct a series of shortwaves from the southern
Plains to the Northeast, bringing periods of snow and ice to
portions of the Upper Midwest, Great Lakes, and Northeast. 
Ongoing precipitation associated with a low-amplitude wave moving
from the Great Lakes into the Northeast is expected to produce
some additional light snow and ice accumulations across portions
of eastern Upstate New York into central and northern New England
later this morning.  This system will be quickly followed by
another low-amplitude shortwave lifting northeast through the Ohio
Valley into the Great Lakes.  By this afternoon, precipitation
will begin to spread back into the Northeast along a lingering
frontal boundary.  All rain is expected across much of New York. 
However, further east, a lingering wedge of cold air will support
snow changing to freezing rain across portions northern New
England, remaining mostly snow across northern Maine.  WPC PWPF
shows probabilities above 50 percent for ice accumulations of 0.10
inch or more centered over central New Hampshire on Day 1.  Snow
accumulations with these two systems are expected to remain light,
with probabilities for accumulations of 4 inches or more remaining
less than 10 percent through Day 1.  Meanwhile, a light wintry mix
is expected to develop within the wave's deformation zone,
producing some minor ice accumulations from Iowa to Lower Michigan.

A more amplified shortwave is forecast to lift out of the southern
Plains on Thursday, reaching the Great Lakes by Friday morning. 
This will bring the next round of precipitation into the
Northeast.  A wedge of cold air associated with high pressure
sliding east across Quebec into Atlantic Canada will support a
wintry mix across the Adirondack region into Vermont, New
Hampshire, and northwestern Maine.  Precipitation is expected to
fall mostly as snow across northern Maine as a developing coastal
helps to lock in the cold air.  WPC PWPF shows probabilities of
10-30 percent for ice accumulations of 0.10 inch or more centered
over northern New Hampshire into northwestern Maine on Day 3. 
Probabilities above 50 percent for snow accumulations of 4 inches
or more are centered over Aroostook County.

Pereira