Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
343 AM EST Tue Mar 02 2021

Valid 12Z Tue Mar 02 2021 - 12Z Fri Mar 05 2021

...Upstate New York...
Days 1-2...

A clipper type low will dive quickly out of Canada while weakening
beneath a modest shortwave through tonight. Generally fast flow
and modest ascent with limited moisture will preclude much in the
way of heavy snowfall across most of the area. However, pronounced
NW flow beneath subtle height falls should allow for some
enhancement in the favored upwind terrain on the north sides of
the Adirondacks and Tug Hill Plateau. Light synoptic snow plus
this enhanced upslope should produce modest accumulations through
early Wednesday in these areas. WPC probabilities for 4 inches are
as high as 60%.

...Four Corners...
Days 2-3...

A strong closed low moving into Southern California Wednesday
evening will drive ascent into the Four Corners region as
mid-level diffluence, height falls, and backed winds on WAA
combine. Pacific moisture flooding into the area cyclonically
around this feature will allow precipitation to expand Wednesday
night into Thursday, aided by weak surface cyclogenesis in the lee
of the Rockies. This Pacific air will cause snow levels to rise to
6000ft or more, so heavy snow should be confined to the higher
terrain of the eastern Great Basin and southern/central Rockies.
The heaviest snow is likely in the San Juans which will benefit
from upslope on southerly 700mb flow, and WPC probabilities here
are as high as 60% for 6 inches on D2.5. Otherwise, WPC
probabilities indicate a moderate chance for 4" in the Wasatch,
Mogollon Rim, and into much of the CO ranges.


...Pacific Northwest...
Day 3...

A closed mid-level low will approach Washington and Oregon late
Thursday night accompanied by a Pacific jet streak and warm/moist
mid-level SW flow. The slow eastward progression of this feature
will allow for significant precipitation to spread across the
coast of WA and OR much of D3. However, snow levels are likely to
climb above 4000 ft, limiting significant snowfall to the Olympics
where WPC probabilities are high for 6 inches, and more than 12"
is possible in the highest terrain.


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

Weiss