Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
348 AM EST Sat Feb 29 2020

Valid 12Z Sat Feb 29 2020 - 12Z Tue Mar 03 2020


...Western U.S....
Days 1-3...

A potent shortwave digging along the California coast through
early Sunday will deepen and close off as it traverses southern CA
on Monday and drops into Baja Tuesday. At the same time, a
pronounced and robust subtropical jet will streak west to east
across the southern tier of the CONUS through Sunday, and begin to
lift poleward in response to the deepening and southward advection
upper trough the latter half of the forecast period. The
combination of height falls, mid-level divergence ahead of the
closed low, and modest coupled jet structure producing diffluence
will lead to large scale ascent across the West, with a focus of
moisture funneling on SW 700-500mb flow into the Central Rockies.
In addition, a low-level front will drop out of the Northern
Plains producing a stripe of low-level fgen sinking southward into
the Four Corners and central High Plains, acting to intensify the
WAA/isentropic ascent, with upslope easterly flow developing in
its wake.

This best overlap of synoptic ascent enhanced by mesoscale forcing
via fgen or upslope is likely across Wyoming and Colorado, where
WPC probabilities for 8 inches are high on D2 from the Laramie
Range southward into parts of the northern Colorado Rockies, and
event total snowfall may exceed 12 inches in places. Heavy snow is
also likely across the Uintas and Wasatch in Utah, the Sierra of
California, and ranges of eastern Nebraska where WPC probabilities
for 6 inches are high Sunday into Monday. The best ascent will
wane by D3 as the upper low begins to kick out to the east across
northern Mexico, but another shortwave diving through the
mid-level confluent flow into the PacNW will bring renewed heavy
snow to the Cascades where WPC probabilities for 6 inches are high
Monday and Monday night.


For Days 1-3, the probability of significant icing (0.25-inch or
greater) is less than 10 percent.

Weiss