Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
325 PM EST Fri Dec 08 2023

Valid 00Z Sat Dec 09 2023 - 00Z Tue Dec 12 2023


...Northern Plains into Upper Midwest...
Day 1...
A shortwave trough currently centered over the northern Plains is
expected to deepen this evening, with a closed 500mb low forecast
to develop near the North Dakota-Minnesota border.  Models have
shown a notable increase in QPF and snow within the associated
deformation band, supported in part by the favorable forcing aloft
overlapping low-to-mid level frontogenesis.  The latest HREF
guidance shows snowfall rates of 0.5-1 in/hr translating east from
eastern North Dakota into northwestern Minnesota during the
evening and overnight hours.  WPC guidance now shows high
probabilities (greater than 70 percent) for accumulations of 4
inches or more extending from east-central North Dakota into
northwest Minnesota.  Embedded within this area are some moderate
probabilities (greater than 40 to 70 percent) for accumulations of
8 inches or more.

...Pacific Northwest through the Northern Rockies...
Days 1-3... 

Mid-level shortwave will move into southwestern British Columbia
mid-day Saturday at the nose of a 130kt jet streak. Parent surface
low will track into the southern Alaska Panhandle with the surface
warm front coming ashore in the afternoon. Moisture surge from the
northeastern Pacific (PW anomalies +1 to +2 sigma) will bring
another round of snow to the region, with lower snow levels to
start (below most passes, around 3000ft) thanks to the in-situ
colder air mass. Warm front will help raise snow levels above
6000ft by early Sunday as 700mb temperatures rise past -5C (+1
sigma). The whole system will be stretched out into Monday as the
dynamics weaken at the expense of the developing Eastern US
system, but the onshore flow will continue to produce light to
modest snow through Sunday into Monday over the Cascades and
eastward into the Blue Mountains, Salmon River, Sawtooth, and
remaining Northern Rockies. Remaining weaker height falls will
also bring snow to western WY on Sunday into Monday. WPC
probabilities for at least 8 inches of snow during the period are
high (>70%) generally above 4500-5000ft over the Cascades into the
Blue Mountains and northern/central ID. Probabilities for at least
8 inches are moderate (40-70%) over western WY.

...Utah, Colorado and South-Central High Plains... 
Day 1... 

Broad multi-vort trough will continue to move through the central
Rockies/Front Range this afternoon and overnight, supporting
generally light to moderate snow as the LFQ of an approaching
130kt jet moves through UT. Snow will focus over the northern CO
ranges and also along the I-25 corridor this afternoon/evening
with some NNE flow well behind a surface cold front over the
Plains. Precipitation shield will sink south-southeastward
overnight before dissipating on Saturday as a strong surface high
pressure moves into the region. WPC probabilities for at least 4
inches of snow are moderate (40-70%) or higher from near and south
of Denver southward to the Raton Mesa.

...Central Appalachians through the Interior Northeast...
Day 3...
Energy currently centered over the northern Plains is forecast to
move farther east and north into the Great Lakes and eastern
Canada on Sunday.  Meanwhile energy over the western U.S. will dig
to the south, contributing to a sharp positively-tilted trough
extending from the Great Lakes to the western Gulf Coast early
Sunday.  Energy moving through the base of the trough is forecast
to assume a negative-tilt as it swings across the southeastern
U.S. Sunday evening, spurring the rapid development of a surface
low tracking north along a sharp cold front, with guidance
continuing to show a powerful cyclone tracking across New England
on Monday.  The deepening low will direct moisture onto the cold
side of the front, supporting rain changing to snow beginning
Sunday evening across the southern to central Appalachians, before
moving north through the interior Northeast Sunday night and
Monday. The heaviest amounts are expected to center across
northern Upstate New York and northern Vermont where a coupled
upper jet and strong low-to-mid level frontogenesis are forecast
to support heavy rates on the backside of the low.  The latest WPC
guidance is showing moderate to high probabilities for
accumulations of 8 inches or more across this area.

This is expected to be a fast-moving storm, with the surface low
moving quickly into eastern Canada by Monday evening.  However,
strong northwesterly to westerly flow in the wake of the system
will support lake effect and orographic snows, contributing to
additional amounts in the lee of the lower Great Lakes and over
northern New England late in the period.

Pereira/Fracasso