Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
603 AM EDT Sun Oct 27 2024

Valid 12Z Sun Oct 27 2024 - 12Z Wed Oct 30 2024


...Pacific Northwest to the central Rockies...
Days 1-3...

A frontal band associated with a low moving into British Columbia
will continue to produce widespread precipitation across the
Pacific Northwest and northern California today. Ample moisture,
along with mid-level energy embedded within deep onshore flow, will
support areas of moderate to heavy precipitation in the favored
terrain early in the period. Snow levels, starting above 6000 ft
along much of the Washington and Oregon Cascades, will steadily
drop through today, dipping into the 4000-5000 ft range across much
of the region by early Monday. While the heaviest precipitation is
expected to fall this morning along the front, persistent onshore
flow in its wake will support continued unsettled weather. Heavy
snow accumulations are expected to remain above the major passes,
however some light amounts are possible by Monday morning.

As onshore flow and unsettled weather continues Monday into
Tuesday, probabilities for at least a few inches of snow are
expected to increase in the Cascade Passes. Meanwhile, as the
upper trough and its associated front move further inland, mountain
snow is forecast to develop father south and east from the Sierra
Nevada to portions of the northern and central Rockies. WPC
probabilities continue to highlight the southwestern Montana ranges
as one area that could see locally heavy accumulations by early
Tuesday. Supported by a weak wave moving along the low level front,
WPC probabilities indicate that locally heavy amounts of 6 inches
or more are likely, especially for areas above 8000 ft. Further to
the south, deep southwesterly flow, along with strong forcing
ahead a well-defined shortwave moving through the base of the
broader scale trough, are expected to generate some heavy totals
over the San Juans in southwestern Colorado.

As the previously noted shortwave continues to translate through
the base of the trough and lift northeast from the Southwest,
the potential for heavy snow is expected to expand across a larger
portion of the central Rockies on Tuesday. Increasing upslope flow
on
the north side of a developing low level wave moving across
Wyoming, along with favorable upper forcing will likely support
locally heavy accumulations across some of the western and central
Wyoming ranges. This includes the Wind River and Big Horns, where
probabilities for accumulations of 8 inches or more are above 70
percent for some of the higher elevations. Other areas that will
likely be impacted include the Uintas in northern Utah and the
Black
Hills along the Wyoming-South Dakota Border, where WPC
probabilities for accumulations for accumulations of 8 inches or
more are above 50 percent for parts of those regions.

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

Pereira