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Winter Weather Forecast Discussion
 
(Latest Discussion - Issued 0748Z Apr 04, 2020)
 
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Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
348 AM EDT Sat Apr 04 2020

Valid 12Z Sat Apr 04 2020 - 12Z Tue Apr 07 2020


...Western U.S....
...Late Season Heavy Snow for higher California Mountains...

Days 1-3...
Successive lows off the northern California coast (the latter of
which becomes cutoff and drifts with the coast) are forecast to
bring late season heavy snows to the southern Cascades, Klamath
and Shasta/Siskiyous, the entirety of the Sierra Nevada, and
higher southern California mountains through Monday night. The
highest amounts are expected in the Shasta region and along the
Sierra Nevada where 2 to 5 feet are likely.

A compact shortwave low swings east into the coastal border of
CA/OR today, weakening as it pushes through a ridge before
reaching the northern Rockies tonight. This initial system will
have an enhanced swath of Pacific moisture (PW above 0.75in)
across northern CA with a quick hitting heavy snow above the
4000ft snow level for the Klamath, Shasta/Siskiyous, Trinity Alps,
southern OR and CA Cascades today, spreading south to the northern
Sierra Nevada tonight. The combination of the weakening low,
higher snow levels, and much of the moisture precipitated in
CA/OR, little heavy snow risk exists over the northern Great Basin
with Day 1 snow probs limited to the aforementioned mountains with
high probabilities for 8 or more inches.

The second, stronger low approaches the far northern CA coast late
tonight, nearly stalling through Sunday night before drifting
south and slowly weakening as it reaches a point off the central
CA coast Monday night. The narrow corridor of enhanced Pacific
moisture plume is maintained south of this low with considerable
moisture flux into CA through the forecast period. Snow levels are
expected to be 3000 to 4000ft near the low/coast and 4000 to
5000ft over the Sierra Nevada and southern CA mountains (on Day
3). Day 2 snow probabilities for 8 or more inches are similar to
Day 1 (high) over far northern CA with the entirety of the Sierra
Nevada in heavy snow from the slow moving low and continued influx
of enhanced moisture. The Sierra Nevada have high probabilities
for 18 or more inches on Day 2 and 2 to 4 feet are likely over the
High Sierra. High Day 3 snow probabilities for 8 or more inches
are focused on the southern half of the Sierra Nevada and the San
Bernardino Mtns (particularly near Big Bear), along with the White
Mtns and the ranges of central Nevada (all within the main plume
of Pacific moisture). Speaking of this plume, the Day 2.5 time
frame is best for moisture intrusion across the Great Basin with
moderate probabilities for 8 or more inches for the Sawtooth Mtns
of ID and the Tetons in WY.

Jackson