Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
347 AM EDT Mon Apr 01 2019

Valid 12Z Mon Apr 01 2019 - 12Z Thu Apr 04 2019

...Oregon/California to the North and Central Rockies...
Days 1-3...

Surface low pressure approaches the CA/OR border today before
moving onshore Tuesday. Atop this feature, Pacific jet energy and
a parent shortwave will dig into California while weakening,
spreading moisture as far inland as the Panhandle of Nebraska. The
moist advection south of these features will drive anomalously
high PWAT air into the West, but snow levels will be above 7000 ft
initially, limiting snow to the highest terrain of the Sierra
where WPC probabilities are low for 8 inches. Beyond Monday into
Day2/Day3, the trough shifts inland causing snow levels to drop at
least slightly to 5000-7000 ft. This will spread the heavy snow
inland, with the heaviest snow expected from the Sierra to the
Uintas, Wind Rivers, Laramies, and CO Rockies on Tuesday, shifting
further east and starting to ease on Wednesday. WPC probabilities
are highest for 6 inches across these ranges on Day 2, and 3 day
snowfall totals may exceed 1 foot in a few of the ranges.


...Western Carolinas...
Days 1-2...

A surface low pressure will move northeast from the N FL coast
this evening to off the Outer Banks of NC Tuesday evening. As this
low moves up the coast, it will interact with a shortwave ejecting
from TX and enhanced jet level diffluence to deepen, and spread
moisture NW into the Carolinas. Although there remains
considerable spread among the guidance, with the NAM a consistent
but western outlier, and the GFS on the eastern edge of the
envelope, confidence is increasing that some snow is possible in
the upstate of SC and into the southern foothills of NC.
Temperatures will be marginal so snow will be dependent on dynamic
and wet-bulb cooling, and QPF will feature a sharp gradient, but
WPC probabilities have increased to 20-30% for 1 inch late Monday
night into early Tuesday afternoon. Although this is below
watch/warning thresholds, 1" in April is rare for this area so
would be significant if it occurs.


The probability for significant freezing rain (0.25 inches) is
less than 10 percent all 3 days.


Weiss