FOUS11 KWBC 240835
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
335 AM EST Sun Nov 24 2024

Valid 12Z Sun Nov 24 2024 - 12Z Wed Nov 27 2024

...Northern New England...
Days 1-2...

Upper low moving over Atlantic Canada is expected to stall today
and absorb approaching upper shortwave diving southeastward over
Ontario. These features combined with strong northwest flow will
support upslope snow over the higher terrain of far northern New
England (mainly the White Mts through northern Maine). WPC
probabilities of an additional 4 inches of additional snow are
medium (40-70%) over these areas. Light snow is also favored over
eastern NY (Adirondacks into the Catskills) but amounts should be
under 4 inches.

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

Tonight, energy from two separate disturbances, one an upper level
low over the Canadian prairies, and the other an ejecting
shortwave out of central Great Basin, will merge over a strong
surface cold front diving southward over the central Plains. An
area of low pressure will then form and progress northeastward from
the Midwest to the Great Lakes on D2. The combination of upper
level energy and upper diffluence beneath the favorable left- exit
region of a quick moving 250 mb 105 kt jet streak will aid in a
blossoming precipitation shield from northern MN to northern WI and
the U.P. of Michigan into Monday morning. As the low tracks
northeast across the L.P., much colder air wrapping around the back
side of the low will allow for additional widespread lake-effect
snow and snow showers persisting into D3 for much of the U.P. WPC
probabilities for at least 4" of snow are medium (30-60%) across
the Arrowhead of MN, far northern WI, and the U.P. of Michigan.

As this low and precipitation moves eastward over the Northeast
and New England on D3, light freezing rain is possible over
interior New England as low- level cold air remains locked in
place as mid- level temperatures rapidly warm above freezing along
with the precipitation shield. Surface temperatures should also
eventually rise above freezing given the strong low forecast to
track north of the region into southern Quebec. Only the northern
White Mts and far northern Maine could see temperatures remain
around the freezing mark and the entire column potentially
remaining cold enough for light snow.

...Sierra, Wasatch, CO Rockies...
Days 1-3...

Ejecting upper shortwave and surface cold front crossing the
Intermountain West and central Rockies today will include residual
moisture from the atmospheric river impacting northern California
over the last few days and will have the potential to produce a
burst of snow over the region. Snow levels starting around
5000-6000ft will fall below 4500-5000ft by the end of D1 and
behind the cold front, but also as the column gradually dries out.
WPC probabilities for at least 6 inches of snow are mostly low
(10-30%) for the Wasatch Mts and CO Rockies, with higher chances
above 9000ft.

Troughing off the West Coast will continue during the short range
period, with a rather steady stream of moisture into the region.
Generally lighter snow is forecast for D1 above 4000ft or so
over northern CA and the Cascades WPC probabilities for at least 6
inches of snow are medium (40-70%) for these ranges and high
(>70%) above 6000ft. By D2, the next heavy snow event enters the
West as another surge of moisture will aim toward the Sierra with
PW and IVT values climbing above the 95th percentile per the NAEFS
ESAT. With a favorable WSW flow into the central/southern Sierra,
moderate to very heavy snow is likely for areas south of Lake Tahoe
into D3 as PW/IVT anomalies peak above the 99th percentile. Snow
levels will rise well above 7000ft to 9000ft (north to south) but
those high elevations may see several feet of snow over the two-day
period. WPC probabilities for at least 24 inches of snow are
highest above 8000ft with the highest peaks possibly receiving
closer to four feet.

Farther east, 120-140kt upper jet will stream across the Great
Basin with the axis of moisture focused across southern NV/UT. This
will set up favorable westerly flow into the Wasatch and then the
CO Rockies with moderate-to-heavy snow accumulations on D3 as snow
levels increase (7500-9000ft). The extended duration of elevated
moisture and favorable westerly flow could lead to higher
elevations receiving multiple feet of snowfall by the end of the
event on Thursday. Currently, WPC probabilities for at least 12
inches are >50% above 9000ft in the CO Rockies and Wasatch MTs
through Wednesday morning.


Snell



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