Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
350 AM EDT Fri Apr 21 2023

Valid 12Z Fri Apr 21 2023 - 12Z Mon Apr 24 2023

...Northern/Central Rockies...
Days 1-2...

A sheared and weakening vort max over the northern Rockies this
morning will continue southeastward and eventually dissipate as it
slips toward the High Plains by early Saturday. Despite limited
moisture and weakening dynamics/upper support, upslope will
provide added lift and the terrain of western MT/WY into northern
UT will see several inches of snow this morning into the
afternoon. Snow will continue to spread quickly southeastward
across the CO Rockies and even into the Foothills after dark, with
the highest amounts generally above 8000ft in the Park Range, Flat
Tops, and Sawatch Range. Snow will come to an end over CO through
the day Saturday. WPC probabilities for at least 4 inches of snow
are high (>70%) above about 8000-9000ft.


...Northern MN and the U.P. of Michigan...
Days 1-2...

Mature, occluded, and stacked cyclone over MN/WI early this
morning will slowly wobble eastward over the next 24 hours in
concert with the upper low. Cyclonic flow will continue to bring
in sufficiently cold air over the eastern Dakotas and into MN with
generally light snow and snow showers through the D1 period in the
unstable air mass. Into D2, the upper low will weaken and move
across Lower Michigan but continued northerly flow across Lake
Superior will support lake enhanced snows on Saturday in the
western U.P. (Porcupine Mountains), across the Keweenaw Peninsula,
and toward the Huron Mountains. Amounts will be light both days,
and WPC probabilities for at least 4 inches each day will be less
than 50%.


...Pacific Northwest...
Day 3...

Compact/small upper low is forecast to come into coastal WA toward
the end of the period, with light snow for the Cascades where WPC
probabilities for at least 4 inches are generally less than 50%.


The probability of significant icing greater than 0.25" is less
than 10 percent for Days 1-3.


Fracasso