Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
442 AM EDT Wed Apr 12 2023

Valid 12Z Wed Apr 12 2023 - 12Z Sat Apr 15 2023

...Pacific Northwest...
Day 1...

A closed upper low will push over NW OR this morning. Snow levels
will dip to 1000ft or locally less under the upper low center.
There are moderate probabilities for ?4" additional snow over the
OR and southern WA Cascades. Probabilities for >2" extend down
into the Columbia Gorge.


...Rockies and the Northern High Plains...
Days 1-3...

The upper low over OR swings east to Idaho through tonight before
pivoting northeast over south-central/eastern MT Thursday/Thursday
night, while also taking on a subtle negative-tilt within the
larger-scale trough. Ample Pacific-sourced moisture will focus
over the northern Rockies Wednesday night/Thursday with lee-side
cyclogenesis increasing NEly flow over mainly MT ranges along with
additional moisture from the western Gulf via the Plains. High Day
1.5 probabilities for >6" are over most SW/central MT and around
Yellowstone in WY, with moderate probs of at least 12" of snow
those parts of MT above 6000ft. The heavier Thursday precip should
be limited a bit in snow accum Thursday, but rates do look heavy
enough to overcome the strong diurnal. Day 2 snow probs low to
moderate for >4" over the Plains of north-central and NE MT. While
areas of higher terrain stand out in the probabilities, where the
bands set up there should be sufficient cooling to allow snow
accum.

As the mean trough axis shifts east to the Rockies on Friday, lift
and moisture result in CO Rockies snow. Post-frontal flow has a
bit of an easterly component with low to moderate Day 3 snow probs
over >6" focused along the Front Range.


The probability for icing over 0.1" is less than 5% Days 1-3.


Jackson