Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
335 AM EDT Mon May 6 2024

Valid 12Z Mon May 06 2024 - 12Z Thu May 09 2024

...Cascades through Rockies...
Days 1-3...

A negatively-tilted upper trough will continue to deepen as it
moves from the Great Basin this morning, with a closed low centered
over eastern Wyoming forecast to develop later today. This will
bring areas of high elevation heavy snow to locations that include
the northern Utah, western to central Wyoming, and north-central
Colorado ranges. WPC PWPF indicates that portions of these areas
are likely to see snow accumulations of 8 inches or more today. As
the system moves east of the Rockies it will begin to tap a plume
of deep moisture surging north through the Plains. Drawn into an
area of impressive lift, this moisture will support the development
of widespread moderate to heavy precipitation, but with high snow
levels, this will be an all rain event for the High Plains.

Meanwhile, a mid-level shortwave and upper jet diving southeast
from the northeast Pacific will bring additional snow showers from
the Cascades to the northern Rockies. As snow levels drop, portions
of the Cascades, especially the Oregon Cascades above 4000ft,
could see several more inches of snow, to over a foot in some
locations today.

Back to the east, the upper low developing over the High Plains
later today is forecast to slowing lift to the north into eastern
Montana tonight before drifting back to the west as it interacts
with a blocking high to its north. This will shift the focus for
heavier precipitation further west into central and western
Montana. Snow levels between 3000-4000ft are expected to increase,
but hover between 4000-5000ft on Tuesday into early Wednesday,
supporting heavy accumulations in the Glacier NP region and across
the Little Belt and Highwood mountains. WPC PWPF indicates that
accumulations of a foot or more are likely across portions of these
areas by early Wednesday. Snow levels are expected to climb across
the region as the low gradually weakens and settles south on
Wednesday, but not before several more inches of snow are likely
to
accumulate across the Little Belt Mountains. As the low settles
south, this is expected to support an increase in precipitation and
the potential for heavy snow across the southwestern Montana and
northwestern to north-central Wyoming ranges, including the
Absaroka and Big Horns.

The probability of significant icing across the CONUS is less than
10 percent.

Pereira