Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
310 AM EDT Fri May 3 2024

Valid 12Z Fri May 03 2024 - 12Z Mon May 06 2024

...Cascades through Sierra Nevada and Intermountain West...
Days 2-3...

An upper low will continue to deepen as it drops southeast from
the Gulf of Alaska and across the northeastern Pacific today,
reaching the Pacific Northwest tonight. Models continue to
advertise an anomalously deep system for early May, with 500mb
heights dropping 2-3 standard deviations below normal across Oregon
and northern California as the system moves onshore. This system
will bring widespread precipitation and windy conditions across the
region, beginning in the Pacific Northwest and northwestern
California tonight, before spreading further south and east on
Saturday. As snow levels drop below 5000ft from the southern
Cascades to the northern Sierra, impactful accumulations are
expected in the higher terrain on Saturday. The heaviest amounts
are most likely to fall along the Sierra Nevada, where left-exit
region upper jet forcing in addition to strong upslope flow are
expected to help bolster rates. WPC PWPF shows high probabilities
for 8 inches or more falling along the northern to central Sierra
in areas above 5000ft on Saturday. Heavier accumulations of 1-2ft
can be expected across some of the higher peaks. In addition to the
falling snow, gusty winds and blowing snow are forecast to
contribute to moderate winter storm impacts as indicated by the
WSSI.

The system is forecast to gradually weaken and transition to an
open wave as it swings east across the Great Basin into the central
Rockies on Sunday into early Monday. Widespread heavy snow
accumulations are not expected, although some portions of the Great
Basin into the Rockies could see some locally heavy totals. This
includes the eastern Oregon, northern Nevada, and northern Utah
mountains.

The probability of significant icing is less than 10 percent.

Pereira