Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
442 AM EDT Wed Mar 27 2019

Valid 12Z Wed Mar 27 2019 - 12Z Sat Mar 30 2019


...Pacific Northwest and Northern California to the
Northern/Central Rockies and High Plains...

A vertically-stacked low over the eastern North Pacific ocean will
gradually weaken as it meanders toward the Pacific Northwest coast
this period.  Shortwave energy moving south of the low will send
another occluded frontal band into northern California later
today.  Strong moisture transport, supported by deep southwesterly
flow, interacting with divergent flow aloft is expected to
generate widespread precipitation, with orographic enhancement
producing some locally heavy totals.  Snow levels begin above 5000
ft and then lowers to around 4000 as the front pushes through the
area tonight.  Along the western slopes of the northern Sierra,
WPC Day 1 probabilities (ending 12Z Thursday) show a Moderate Risk
for accumulations of a 8-inches or more for areas above 6000 ft,
with a High Risk for a foot or more across a few of the higher
peaks.

Post-frontal showers are expected to continue, possibly producing
additional locally heavy totals along the Sierra.  However with
onshore flow weakening, the potential for widespread additional
heavy amounts is expected to decrease on Thursday.

Farther to the northeast, moisture spreading inland will move
underneath strengthening divergence aloft associated with the
left-exit region of an upper jet extending out ahead of the low. 
That, combined with strengthening low-mid level frontogenesis and
upslope flow, is expected to support locally heavy snow totals
over portions of the northern Rockies - particularly the ranges of
southwestern Montana and northwest Wyoming.

As the leading shortwave moves across the northern and central
Rockies, snows are expected to spread southeast across of the
Divide.  There is a fairly good model signal for moderate to heavy
snows developing over the central High Plains from southwestern
South Dakota, southeast Wyoming, across the much of the Nebraska
panhandle and out over the plains of western Nebraska....with one
Moderate Risk area of 4 inches extending as far east as the 100th
meridian. 

Bann