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

Valid 00Z Sat Apr 22 2023 - 00Z Tue Apr 25 2023

...Central Rockies...
Days 1-2...

A sheared and weakening vort max spanning the length of the U.S.
Rockies this afternoon will continue gradually dissipating while
also sliding southeastward tonight in response to a deep cutoff
upper-level low over the Upper Great Lakes. Despite limited
moisture and weakening dynamics/upper support, upslope will
provide added lift in the terrain of WY and CO tonight. 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.
A few inches of snow are possible across the CO Foothills within a
brief period of favorable banding potential tonight under a
right-entrance region of the weakening jet streak. WPC
probabilities for at least 4 inches of snow are high (>70%) above
about 8000-9000ft.

...U.P. of Michigan...
Day 1...

Mature, occluded, and stacked cyclone over far northern MN this
afternoon will slowly wobble eastward over Lake Superior tonight
before merging with a developing surface low over southeast
Ontario on Saturday. Cyclonic flow will continue to bring in
sufficiently cold air over the northern Plains and eventually the
Upper Great Lakes with light snow showers ending this evening in
the unstable air mass. On Saturday, in response to the upper low
weakening and moving across Lower Michigan, continued northerly
flow across Lake Superior will support lake enhanced snows into
the western U.P. (Porcupine Mountains), across the Keweenaw
Peninsula, and toward the Huron Mountains. Amounts will be
generally light both days, with the highest WPC probabilities
(40-50%) for at least 4 inches centered across the western U.P.


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

Compact/small upper low is forecast to come into coastal WA toward
the end of the period (Monday), with light snow for the Cascades
and Clearwater Mountains. 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.


Snell