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

Valid 00Z Sun Mar 01 2020 - 00Z Wed Mar 04 2020


...Central High Plains...Southern and Central
Rockies...Intermountain West...Desert Southwest....
Days 1-2...

A potent positively tilted trough digs southeast to the northern
CA coast tonight...closing off to a low Sunday over the central CA
Coast that then shifts down the CA to northern Baja coast through
Monday before shifting east over northwest Mexico through Tuesday.
A powerful subtropical jet streak blowing west to east in excess
of 150kt persists across the southern tier of the CONUS through
Sunday before tilting southwest ahead of the upper trough Sunday
night through Monday. The combination of height falls, mid-level
divergence ahead of the closing low, and modest coupled jet
structure producing diffluence will lead to large scale ascent
across central portions of The West, with a focus of moisture
funneling on SW 700-500mb flow from the Southwest across the
Central Rockies. In addition, a low-level front will drop out of
the Northern Plains producing low-level frontogenesis sinking
southward over the Great Plains and central High Plains,
intensifying  warm air advection/isentropic ascent, with upslope
northeasterly flow developing in its wake.

This best overlap of synoptic ascent enhanced by mesoscale forcing
via frontogenesis or upslope flow is across WY on Day 1 and CO on
Day 2, where WPC probabilities for 8 inches are high on Day 1 for
the Wind River Range and Tetons with moderate risks for the
Bighorn, Laramie Range southwestward across the Uintas and Wasatch
in UT, and the eastern Nevada ranges. Upslope flow direct from the
Pacific provides enhanced snow on the Sierra Nevada where Day 1
probabilities are moderate to high for 8 or more inches. Moisture
influx and forcing shifts south of the border Monday with Day 2
snowfall probabilities much lower for a stripe south of Day 1 with
moderate probabilities for southern UT/the highest peaks of
northern AZ, and central CO. Upslope northeasterly flow in
northern CO provides some low chance Day 1.5/2 probabilities for 6
or more inches for the Palmer Divide.


...Pacific Northwest...
Days 2-3...

The first of a series of impulses pushes southeast across BC
Sunday night with the next trailing right behind and crossing a
little farther south over BC Monday night. Northwest flow south of
these impulses direct Pacific moisture across WA to the northern
Rockies Monday through Tuesday. The high moisture content will
promote higher snow levels (generally 3000 to 4000ft) and moderate
precipitation for the WA Cascades to the northern ID/northwest MT
Rockies. Day 3 snow probabilities are moderate to high for 6 or
more inches for these mountains.



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

Jackson