Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
432 AM EDT Sun Apr 14 2024

Valid 12Z Sun Apr 14 2024 - 12Z Wed Apr 17 2024


...Northern California across Great Basin and Colorado Rockies...
Days 1-3...

Occluding cutoff low on the northern CA coast continues to fill
today as it drifts east to Nevada. A shortwave rounding the low
currently lifting up the Sierra Nevada maintains a surface low over
the northern Great Basin today, shifting the heavy snow focus from
the Sierra Nevada north over the Shasta/Siskiyou east through the
Warner Mtns in the far northeast corner of CA today with snow
levels remaining around 5000'. Rates within snowbands here peak
early this morning around 1"/hr with Day 1 PWPF for >6" after 12Z
generally 40-70%.

The low will continue an eastward progression through the Great
Basin into Monday with large scale ascent focused over Utah tonight
into Monday before shifting to the CO Rockies Monday night.
Sufficient Pacific moisture allows for peak 1"/hr rates under the
upper low Monday afternoon over the Wasatch and Uinta mountains of
Utah where Day 2 PWPF for >6" is 40-70% with snow levels rising
from 6500' to 7500'.


As the low reaches western CO Monday afternoon, lee-side
cyclogenesis in northeast CO helps direct Gulf-sourced moisture
streaming up the Plains to be drawn over the central Rockies,
enhancing snow for CO Ranges generally west from the Continental
Divide. Snowfall rates peak late Monday night with Day 2.5 PWPF
for >6" in the 50-80% range with snow levels generally 7500'.
Probabilities for >12" are around 50% for the CO Front Range,
Medicine Bow, and Park Range for Day 2.5.


...Northern Rockies...
Day 3...

A northern stream trough currently over the Gulf of Alaska shifts
southeast to southeastern BC by early Tuesday which promoted an
inverted trough up the northern Plains from ND well into
Saskatchewan. By Tuesday night, the upper trough overspreads MT and
enough moisture from the Plains/Prairies rounds the inverted trough
to allow some upslope snow over the eastern side of the northern
Rockies of MT into northern WY. This air will be cold with snow
levels dropping generally from 3500' to 1500' over MT. Day 3 PWPF
for >6" is 40-60% around Glacier NP as well as the Absarokas north
and east of Yellowstone and the Bighorn Range.


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


Jackson