Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
152 PM EDT Sat Apr 11 2026

Valid 12Z Sat Apr 11 2026 - 12Z Tue Apr 14 2026

...Sierra Nevada and Rockies...
Days 1-3...

Anomalously deep low (500-700mb heights below the 0.5 percentile of
the CFSR climatology according to NAEFS) will spin onshore
California north of San Francisco by Sunday morning, and then
gradually weaken into an open trough as it progresses into the
Great Basin on Monday. Despite this steady weakening of the upper
feature, impressive ascent through height falls, PVA, divergence,
and upper jet streak, and strong orographic lift will create
widespread precipitation falling as snow in the higher elevations.
The heaviest snow is likely D1 across the Sierra when the WPC
prototype snowband tool indicates a high chance for 1-3"/hr
snowfall rates as snow levels fall to around 4500 ft beneath the
core of the upper low. This will create dangerous travel across
many of the Sierra Passes, with some of the northern California
passes (through the Shasta/Trinity region) also experiencing
hazardous travel due to heavy snow. WPC probabilities D1 are high
(>90%) for at least 12 inches of snow in the Sierra, with locally
2-3 feet possible before snow wanes quickly during D2. In the
Shasta/Trinity region, WPC probabilities D1 are moderate to high
for 12 inches.

Farther east into the Great Basin and the Rockies, light to
locally modest snow in association with the incoming system will
spread across the region Sunday and continue through Monday. WPC
probabilities for at least 6 inches of snow are >50% above about
8000ft over eastern NV/OR into the central Idaho ranges and above
10,000-11,000ft into the Wasatch and the Uintas.


...Washington...
Day 3...

Pinched mid-level flow south of a closed low dropping south along
the coast of British Columbia will combine with a zonally oriented
Pacific jet streak to drive moisture into Washington D3. This is
reflected by an IVT surge exceeding 300 kg/m/s according to the
West-WRF, with the core of this plume moving onshore Tuesday aftn
before steadily dropping southeast through 00Z/Wednesday. This
will manifest as increasing moisture and precipitation in a
relatively narrow corridor late D3 and continuing beyond this
forecast period. The overall column will be marginal for any wintry
precipitation initially, but as the upper low approaches and a cold
front drops southward, snow levels will fall from 4000-5000 ft to
as low as 3000 ft by 00Z/Wednesday. This suggests most of the
significant accumulations will occur above many of the passes,
where WPC probabilities are 50-70% for at least 6 inches of snow,
but some light/slushy accumulations are possible as low as Stevens
and Snoqualmie Passes very late D3 and into D4 before snowfall
wanes on Wednesday.


...Colorado Rockies...
Day 3...

Closed mid-level low over the Great Basin Monday will open into a
positively tilted trough as it swings eastward, with an embedded
shortwave and vorticity maxima rotating through its base on
Tuesday. While there are considerable amplitude differences
through this evolution, the timing is generally well aligned among
the various ensemble camps, suggesting this shortwave/vorticity
maxima will move into the Central Rockies around 12Z Tuesday. The
corresponding ascent (through height falls and divergence) will
work in tandem with the LFQ of a poleward arcing jet streak to
drive lee cyclogenesis in eastern CO, with this low shifting
rapidly northeast into the Central Plains by the end of the
forecast period.

The mid-level SW flow will transport moisture into the area, while
increasing low-level southerly flow will tap some Gulf moisture as
well. However, the speed of this system ejecting northeast should
limit the ability of the accompanying theta-e to surge into CO, and
this is reflected by PWs that are progged to be around normal
according to NAEFS ensemble tables. Still, sufficient moisture
being wrung out by the impressive synoptic ascent will produce
areas of precipitation across the CO Rockies, with snow falling
above wavering snow levels between 6500-8000 ft. Total snowfall
will be somewhat modest, but WPC probabilities D3 indicate a 50-70%
chance of at least 4 inches across the San Juans and other higher
peaks of western CO.


The probability of significant icing for days 1-3 across the CONUS
is less than 10 percent.

Weiss