Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
347 AM EST Wed Nov 08 2023

Valid 12Z Wed Nov 08 2023 - 12Z Sat Nov 11 2023

...Colorado Rockies...
Day 1...

The base of a positively tilted upper trough axis shifts across
southern UT this morning with central/southern CO in the right
entrance region of a 130kt+ SWly jet streak extending over the
Central Plains. A cold front surging south from central CO this
morning will continue to bring strengthening N-NE low level flow,
providing modest upslope ascent into the Front Range of the
Rockies of CO into northern NM with modest 700mb moisture flux.
Day 1 WPC probabilities show moderate chances (40-60%) of >6"
snowfall along the Front Range and central CO with topping 6",
with 10-30% for >12" in the highest peaks.


...Northern Great Lakes, Northeast...
Days 1-3...

The southwesterly jet over the central Plains shifts east to the
Great Lakes today, then intensifies as low pressure develops over
the Boundary Waters of MN tonight. A warm front at 850mb will
track east into the northern Great Lakes this morning and the
Northeast tonight. Snow currently falling over the U.P. of MI
continues to shift east today with moderate Day 1 probabilities
for for >4" limited to near Sault Ste. Marie.
Meanwhile, a sufficiently cold air-mass anchored by high pressure
centered over northern Quebec lays the ground work for a classic
overrunning setup for the Northeast featuring sub-freezing surface
temperatures and a burgeoning warm nose of >0C temps within the
850-750mb layer. This will result in an icy wintry mix from the
Catskills and Adirondacks to the Berkshires, Green, and White
Mountains. Day 1.5 WPC probabilities depict moderate probabilities
(30-60% chance) for ice accumulations >0.1" in these areas. Light
sleet accumulation can also be expected in these areas of icing.
While snow is likely at onset in interior Northeast locations,
little accumulation is expected out of the higher elevations of
northern New England.

Westerly flow in the wake of the low brings lake effect snow off
Lake Superior Thursday and Friday. Due to marginal thermals, the
only notable snow risk at this point through Day 3 is for the
Porcupine Mtns in the western U.P. of MI.


...Washington...
Days 2/3...

The next frontal system to approach the Pacific Northwest is
associated with a sharp upper trough that approaches on Thursday
that directs Pacific moisture western WA within S-SW prefrontal
flow and then prolonged onshore post-frontal flow. Snow levels
rise to around 4000ft at precip onset Thursday, then drop to
around 3500ft post-frontal Thursday night. Day 2 snow probs are
low-moderate (30-50%) for >6" over the higher WA Cascades then
shift to slower elevations of the Cascades for Day 2.5. With snow
levels reaching mountain pass level, extra caution is encouraged
with overland travel.


Jackson