FOUS11 KWBC 120643
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
243 AM EDT Sun Apr 12 2026

Valid 12Z Sun Apr 12 2026 - 12Z Wed Apr 15 2026

...Sierra Nevada to the Rockies... Days 1-3...

Deep upper low will move into NorCal today and continue to weaken
with its lead surface cold front already moving into/through the
Sierra. Despite this steady weakening of the upper feature,
impressive ascent through height falls, PVA, divergence, an upper
jet streak, and strong orographic lift will create widespread
precipitation falling as snow in the higher elevations. Though some
heavy snow has already fallen, additional modest to perhaps
heavier snow will continue in waves today over the Sierra with
1-2"/hr snowfall rates. Snow levels will fall to around 4500 ft
beneath the core of the upper low and create dangerous travel
across many of the Sierra Passes. WPC probabilities for at least an
additional 12 inches of snow are >50% above about 5000ft or so.

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 today and continue through Monday as broad
SW flow continues. By Tuesday, trailing vorticity on the SW side
of the weakening upper low this morning will move into the Four
Corners, enhancing snowfall over especially southwestern CO, but
more broadly over over the rest of the CO Rockies and also across
the Wasatch and Uintas. Snow levels initially around 8000-9000ft
will fall to around 7500ft by later Tuesday as most of the snow
ends from west to east. WPC probabilities for at least 6 inches of
snow are >50% above about 8000ft over eastern NV/OR into the
central Idaho ranges due to the lead upper trough today into
Monday, and above 10,000-11,000ft into the Wasatch, Uintas, and San Juans.

...Pacific Northwest/Northern Rockies... Day 3...

Troughing over Alaska today will steadily move southeastward along
the BC coast Tuesday, bringing a 105kt jet into western WA. A
modest surge of moisture along/ahead of the cold front (IVT values
around the 90th percentile for mid-April) will support widespread
rain and mountain snow starting around early Tuesday and continuing
into Wednesday. Snow levels initially around 3000ft (Cascades) to
4000ft (Northern Rockies) will fall to around 1500-2000ft in the
Cascades as much colder air works in from the northwest by 12Z
Wednesday (700mb temperatures dropping to around -10C to -14C) as
the cold front reaches the Cascades. This will bring snow to the
passes, though perhaps starting as rain in the lower passes, which
could be significant at higher passes. Through 12Z Wednesday, WPC
probabilities for at least 6 inches of snow are >50% above about
2500ft in the Cascades and 5000-6000ft in the Northern Rockies.


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

Fracasso

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