Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
400 AM EST Mon Mar 06 2023

Valid 12Z Mon Mar 06 2023 - 12Z Thu Mar 09 2023

...West/Rockies...
Days 1-3...

Upper ridging amplifying north over Alaska, even into the Beaufort
Sea, and strong high over Davis Strait (between Baffin Island and
Greenland) will help maintain blocking over the high latitudes
that favors troughing over the western portion of Canada and the
Pacific Northwest through midweek. The existing closed low off the
WA coast will begin to be disrupted today as reinforcing energy
from a deep low over the NW Territories of Canada shears the
offshore low into a wave tonight and then the low itself pushes
inland over OR Tuesday night as the NW Territories low ejects
southwest across western BC. Broad onshore flow up and down the
West Coast will continue to have a focus under the inland shifting
westerly Pacific jet over the Klamath, CA Cascades and northern
Sierra Nevada Days 1-2 where there are moderately high
probabilities for >8" both days. Farther east, moderate snow and
low to moderate >4" snow probs days 1 and 3 are noted over the
Wasatch and along the CO/WY border. With 700mb temperatures below
normal (-1 to -2 sigma), snow levels will generally be below
2000ft.

Thursday looks to be a lone break day for battered CA as brief
ridging overspreads the West Coast ahead of a notable atmospheric
river which has melting and heavy rainfall onto snow pack threats.
Please see the medium range discussion (PMDEPD) for further
forecast information for late in the week.


...Northern Great Lakes Through Northern Mid-Atlantic...
Day 1...

A shortwave trough over the Upper Midwest this morning will
continue tracking east today as it crosses MI. However,
reinforcing energy rounding a low over the Canadian Maritimes is
now expected to amplify this trough tonight as it tracks over the
northern Mid-Atlantic. This will enhance the snow banding
potential with a possibility for 1"/hr rates along the NY/PA
border this evening and accumulating snow now possible late
tonight through NJ. Lake enhancement will continue over the upper
Midwest with moderate probabilities for an additional 4" after 12Z
for northeast WI, the central U.P. and the northern L.P. There are
now moderate probabilities for 4" along the NY/PA border with
probabilities for 2" extending to northern NJ. However, this
narrow banding should be decently heavy and this case should be
monitored.


...Northern Plains...
Days 1-3...

Another round of westerly Pacific jet embedded shortwaves eject
east-northeastward across the north-central Rockies tonight
through Thursday. Particularly high surface pressure/cold air over
the Canadian Prairies will provide cold easterly component flow
while a plume from the western Gulf provides ample moisture for
broad synoptic forced snow that expands across the northern Plains
through midweek. Localized flow enhancement over the Black Hills
both tonight and Thursday will help the likelihood of a foot or
more of snow there through the forecast period. Day 1 snow
probabilities for >4" are moderate in a broken stripe from the
Black Hills through the western Dakotas/eastern MT. This threat
shifts east across the Dakotas for Day 2 with moderately high
probabilities for >4" and low to moderate >4" probabilities extend
from the length of the northern High Plains (eastern MT and WY)
across the Dakotas into MN.


For days 1-3, the probability of significant icing greater than
0.1" is less than 10 percent.


Jackson