Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
254 PM EDT Thu Apr 11 2024

Valid 12Z Thu Apr 11 2024 - 12Z Sun Apr 14 2024

...California...
Days 2-3...

A robust and compact upper low will approach the Golden State late
Friday and result in an unsettled weather pattern this upcoming
weekend. NAEFS shows that by 00Z Friday, 500mb heights within the
core of the upper low will fall below the observed CFSR database
(between 1979-2009) and this will be the case through Friday night.
This impressive upper low for mid-April will also accompany a
strong IVT (topping 300 kg/m/s) surpassing the 97.5 climatological
percentile on NAEFS Friday night and into the day on Saturday. It
is worth noting that this upper low will gradually weaken
throughout the day Saturday, and with the calendar now reading mid-
April, it will be increasingly difficult to see heavy snow
<6,000ft. The heaviest snowfall looks to start Saturday morning
along the coastal range and in the Salmon/Shasta Mountains at
elevations >5,000ft, then in the Sierra Nevada >6,000ft around
midday Saturday. While snow levels will lower to roughly 5,000ft by
Saturday evening as the upper low approaches, the IVT will
gradually weaken and mean 850-500mb flow will be oriented more
parallel to the Sierra Nevada, minimizing the amount of strong
topographic ascent. This should keep heavy snow confined to
elevations >7,000ft through Saturday night and into Sunday morning.
By Sunday, the upper low will be much weaker with the best
vertical ascent located to the north of the 500mb low over the
northern Sierra Nevada. Snowfall rates will continue to lighten up
throughout the day with mainly light accumulations through Sunday
afternoon.

WPC PWPF 48-hour probabilities show moderate-to-high chances
(50-70%) for snowfall totals >8" for elevations >7,000ft in the
central and southern Sierra Nevada, the tallest peaks of the
northern Sierra Nevada, and around Mount Shasta. Probabilities drop
to low chances (10-30%) for elevations between 6,000-7,000ft. The
bulk of the more populated areas of the Sierra Nevada should
generally witness Minor Impacts as a result of the snow, with any
Moderate Impacts confined to the more remote and rugged terrain of
the Sierra Nevada that is >7,000ft in elevation through Sunday.

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

Mullinax