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

Valid 00Z Mon Apr 15 2024 - 00Z Thu Apr 18 2024


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

Current WV satellite depicts our closed upper low entering into
the southern CA coast with expected progression eastward as it
traverses into the Great Basin. Snowfall continues in-of of the
central and northern Sierra with snow levels generally around 5000'
expected thanks to the falling height pattern. Highest
probabilities for >6" of snow remain over the Siskiyou Mountains
and Mt Shasta with PWPF outputs between 50-70% with upwards of 90%
in the tallest peaks. A secondary maxima will be within the central
Sierra due to primed mid- level ascent and a feed of Pacific
moWBCQPFHSDisture into the terrain as PWPF peaks at 50-70%.
Probabilities for >8" are much lower outside the taller peaks, but
generally within the 10-30% range with over 50% located within
locations above 10000' in both regions.

Snow will subside in the Sierra and shift focus eastward into UT
on D2 as large scale forcing increases under the diffluent pattern
of the upper low. Probabilities for >6" are greatest within the
Wasatch down into the ranges of southern and central UT. PWPF
values for at least 6" are between 50-80%, confined to areas above
6500' with the higher elevations above 8000' running closer to the
upper percentile probabilistically.

By D3, attention shifts into the central Rockies within CO as our
upper low continues its progression to the east. Totals within the
the central Rockies are forecasted to be highest thanks to a
combination of the favored upper ascent, as well as aid from lee
cyclogenesis over the Front Range. Solid low to mid-level moisture
transport from the Gulf will funnel into the lee of the Rockies
with primed upslope pattern within the terrain over northern CO.
PWPF for >6" encompasses much of the terrain above 7500' with the
highest probabilities running between 50-80% with upwards of 90% in
the tallest peaks of the Medicine Bow and Park Ranges. The
prospects for >12" are within the aforementioned area as well with
probabilities of exceedance running between 30-60% with best chance
located into the central and southern Medicine Bow mountains.

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

A potent mid-level shortwave will progress out of southeast BC and
make headway into the northern Rockies and adjacent Saskatchewan
by the end of D2 into D3. A combination of strong surface ridging
providing prominent cold air advection for the season along with a
inverted trough located over the northern plains to the southern
prairies of Canada will create a primed upslope enhancement over
the northern Rockies by Tuesday night into Wednesday. PWPF for >6"
is highest within the mountains of southwest MT into northwestern
WY over to the Big Horns, along with Glacier National as snow
levels plummet (Falling 3500' to 1500' by Wednesday AM) due to the
cold air advection regime and falling heights aloft. Probabilities
for at least 6" are between 40-60% for Glacier National Park, and
generally between 50-90% across those areas over into Yellowstone
over to the Big Horn Range by the end of the period.

Kleebauer