Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
348 PM EDT Wed Oct 26 2022

Valid 00Z Thu Oct 27 2022 - 00Z Sun Oct 30 2022

...Pacific Northwest & Central Rockies...
Days 1-2...

The focus in the short range is on an amplifying upper trough in
the Intermountain West that will become a closed low and dive
south and east into the southern Rockies by Thursday. The
evolution of this upper trough will result in falling heights,
crashing snow levels, and robust vertical motion in the upper
levels of the atmosphere. Within the 500-300mb layer, PVA will
result in strong vertical motion while upsloping flow along
topographically-favored terrain enhances snowfall rates. This is
also due to the diffluent left-exit region of a 300mb jet streak
being positioned over the Colorado and northern New Mexico Rockies
late tonight and through midday Friday. Some of the heaviest
snowfall rates may occur in the Sangre De Cristos as the 500mb low
tracks just south of them on Thursday and NNE 700mb moisture flux
increases on the back side of the 700mb low ejecting into the
TX/OK Panhandles Thursday midday and early afternoon. These
variables all support accumulating heavy snow, especially above
6,000 ft. The latest WPC PWPF depicts >50% probabilities of
snowfall exceeding 6" just south of I-70 along the Sawatch Range
and into Grand Mesa. WPC's experimental pWSSI shows 60-70%
probabilities of "Moderate" impacts in these areas, as well as
portions of the San Juans through Thursday. Farther south in the
peaks of the Sangre De Cristos of southern Colorado, similar PWPF
values are present in the northern New Mexico Sangre De Cristos
while pWSSI "Moderate" impact probabilities top out are 30%.

In the Pacific Northwest, a steady diet of Pacific moisture will
stream into the northern Cascades Thursday and into early Friday.
The slug of moisture embedded within westerly flow supports
upslope flow into the northern Cascades and thus the potential for
heavy snowfall rates in the higher elevations >5,000 ft. WPC PWPF
for snowfall probabilities >6"  top out around 30-40% on Thursday
with some residual 10-20% probabilities into early Friday. Drier
mid-level moisture rarives in wake of a passing cold front on
Friday, which will shut off any lingering periods of snow by
Friday evening.


The probability of significant icing is less than 10 percent
nationwide.

Mullinax