Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
423 AM EDT Sun Mar 29 2020

Valid 12Z Sun Mar 29 2020 - 12Z Wed Apr 01 2020



...Northeast...
Days 1-2...

Low pressure moving through the Great Lakes will extend a warm
front into New England. This front will lift slowly northeast,
impeded by a persistent wedge of high pressure which will only
slowly retreat to the east. Along this boundary, a surface low is
likely to develop near Cape Cod before slowly exiting eastward
through Monday. Strong WAA associated with the warm front combined
with increasing isentropic ascent atop the wedge will drive a
burst of heavy precipitation across Northern New England tonight
into Monday. While the column will be marginal for snow outside of
Maine, wet bulb effects should lead to some sleet and freezing
rain, especially in the White Mountains of NH and far western ME.
The freezing rain accretion should be generally less than 0.1
inches, and sleet accumulation will keep snowfall amounts down in
this region as well. Further to the NE into much of central and
northern ME, heavy snow is likely Sunday night into Monday, before
tapering off Monday morning. However, a lingering upper low and
surface trough extending into ME/MA will allow light snow to
persist periodically into Tuesday morning. The most significant
accumulation is likely Sunday night into Monday when WPC
probabilities for 6 inches are high. Additional snowfall Monday
night into Tuesday is likely to be less than 4 inches.


...The West...
Days 1-3...

Two distinct shortwaves will lift onto the West Coast and shift
inland through the forecast period. The first is pivoting onshore
this morning and will split with a weak northern and southern
stream vort max racing eastward. This will spread generally light
snow across the Great Basin and into the Wasatch, with moderate
snow in the Olympics, Cascades, and into the Northern Rockies. WPC
probabilities for 6 inches on D1 exceed 50% only in WA and OR.

A much stronger impulse with associated jet level diffluence, a
surface low, and intensifying moist advection on mid-level
confluent flow will spread heavy snow across much of the terrain
north of 40N latitude from Washington through Wyoming. Snow levels
are expected to drop from around 4000 ft Monday to below 2000 ft
Tuesday across WA, while falling across the rest of the region too
but with subtly higher snow levels. Persistent moist advection and
ascent will periods of heavy snow both D2 and D3, and as 700mb
flow backs to be more southerly, heavy snow will accumulate
rapidly. WPC probabilities on D2 for 12 inches are high in the
Olympics and Cascades of WA/OR, as well as the Sawtooth and Blue
Mountains. By D3, snow accumulations should be a bit lighter, but
WPC probabilities for 8 inches are high from the Olympics and
Cascades of WA, through much of the terrain as far southeast as
the Grand Tetons and Wind Rivers.


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

Weiss