From Mike Powell@618:250/1 to All on Thursday, October 17, 2024 08:58:00
FOUS11 KWBC 170836
QPFHSD
Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
436 AM EDT Thu Oct 17 2024
Valid 12Z Thu Oct 17 2024 - 12Z Sun Oct 20 2024
...Mountain West... Days 1-3...
**First Significant Winter Storm of the Season to Impact much of
the Rockies**
A shortwave trough crossing the PacNW coast this morning will dig
across the Great Basin tonight before closing into a low over
northern Arizona by Friday. This low then stalls/drifts east
through Saturday. Ascent ahead of this trough today will allow
widespread rain and high elevation snow today over the Great Basin
and the northern Absarokas where snow levels will be around
7000ft.
Snow levels ahead of the upper low will be quite high, generally
9000-10000ft over CO and southern WY through Saturday. However,
rapid cooling beneath the approach of the upper low and behind the
cold front should drive snow levels to as low as 4000 ft across the
Great Basin, and 5000-6000ft in UT/northern WY. High moisture flux
ahead of the low means heavy snow is likely to begin just above
these levels.
Day 1 snow probs are over 50% for >8" over the northern Absarokas
and Uinta, spreading through the Wind Rivers/Wasatch Friday/Day
1.5. Day 2 features over 80% probs for >8" in the higher San Juans
of CO where Day 3 probs are around 50% in the prolonged precip
ahead of the stalled low. Major accumulations are likely much of
across the San Juans with local maxima of 2-4 feet. These areas
are also where the greatest impacts are expected as the combination
of modest SLR but heavy precipitation causes WSSI to feature
major impacts during this early season storm.
The probability of significant ice across the CONUS is less than
10 percent.