Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
207 PM EDT Fri Oct 18 2024

Valid 00Z Sat Oct 19 2024 - 00Z Tue Oct 22 2024


...Central and Southern Rockies...
Days 1-2...

An anomalous closed low with 700-500mb heights falling to around
-3 sigma according to the NAEFS ensemble tables will spin slowly
across the Four Corners before beginning to fill and eject into the
central High Plains Sunday night. This slow moving system will
provide ample deep-layer ascent through height falls, mid-level
divergence, and upper level diffluence within a modestly coupled
250mb jet structure. At the same time, moisture advection will
remain pronounced on S/SW flow around the base of the trough and
emerging from the Pacific Ocean, pushing an axis of PWs reaching +2
sigma into the Central Rockies, and even +3 sigma across the
central High Plains. The overlap of this significant ascent and
moisture will produce an expansive area of precipitation in the
form of rain and snow through Saturday.

Snow levels have trended warmer the past few runs, so the coverage
of heavy snow has decreased a bit in terms of areal footprint,
generally being confined to above 7000 ft in the Great Basin and
rising to around 10,000 ft in the eastern Four Corners. This
suggests any heavy snow will be confined to just the higher terrain
D1 before waning during D2, with heavy snow accumulations likely
across portions of the Wasatch, Kaibab Plateau, San Juans, and
Sangre de Cristos. WPC probabilities D1 for more than 6 inches of
snow are above 70% in these ranges (30% along the Kaibab Plateau),
and fall to just 30-50% for an additional 6 inches D2 only in the
San Juans. Storm total snowfall will still be significant though,
reaching 1-2 feet in the Sangre de Cristos, and locally as much as
3 feet in the San Juans.

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

Weiss