Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
428 AM EDT Thu Apr 13 2023

Valid 12Z Thu Apr 13 2023 - 12Z Sun Apr 16 2023


...Central and Northern Rockies into Northern and Central Plains...
Days 1-3...
A 700mb low associated with a well-defined shortwave moving east
of the Cascades is expected to track northeast from southwestern
to northeastern Montana today.  Low level frontogenesis combined
with favorable upper forcing is expected to support moderate to
heavy snow northwest of the low, with the latest HREF guidance
indicating rates of 1-2 inches/hr.  With snow levels dropping
below 4000 ft across much of the region, WPC probabilities
indicate that widespread amounts of 4 to 8 inches, with locally
higher totals are likely for the southwestern to central Montana
mountains today.   Generally lighter totals are expected farther
northeast over the high plains of northeastern Montana.  Snows are
expected to diminish from southwest to northeast as the wave lifts
north into southern Canada this evening.

Meanwhile, upstream energy will continue to maintain a broad
trough in the West as it dives southwest through the Pacific
Northwest and Intermountain West.  As the trough amplifies and
moves east, this will produce snows across the Wyoming and
Colorado ranges on Friday into early Saturday.  While widespread
heavy totals are not expected, some high elevation areas could see
locally heavy amounts.  This includes the Colorado Front Range,
where a period of post-frontal upslope flow, enhanced by a low
level wave moving along the boundary, is contributing to higher
probabilities for heavier amounts.

Models show the trough continuing to amplify as it moves east of
the Rockies, with a closed center beginning to form over the mid
Mississippi Valley late in the period.  This will likely support
the transition to some wet snow along the western edge of the
associated precipitation shield overnight Saturday into early
Sunday.  While some models are more bullish than others, forecast
confidence and probabilities for any significant accumulations are
low through early Sunday.

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

Pereira