Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
348 PM EDT Tue Mar 19 2019

Valid 00Z Wed Mar 20 2019 - 00Z Sat Mar 23 2019


...California/Great Basin/central to southern Rockies....

...Day 1...
The models continue to show a negatively-tilted trough swinging
east into California late tonight through Wed.  Initial warm
temperatures leave snow levels high, with accumulating snows
primarily in the Sierra and Mt. Shasta, with WPC Day 1
probabilities indicating a Moderate Risk for areas above 8000 ft.

...Day 2...
As the trough moves slowly inland, the models show a closed 700 mb
low developing over the lower Colorado basin late Wednesday-early
Thursday.   Enhanced moisture and areas of ascent rotate around
the low and move up from Arizona up into UT and CO.  Snows are
expected persist early in the period across the Sierra and then
move farther east into the central Nevada, Utah, and southwest CO
ranges, with WPC Day 2 probabilities indicating a Moderate Risk
for accumulations of 4-inches or more for portions of these areas.


...Day 3...
The upper low drifts east across the Great Basin, so the snows
persist early and taper in the ranges of NV while lasting longer
in the mountains of UT and CO, spreading down in the ranges of
northern NM.  Left-exit region upper jet forcing is expected to
support accumulating snows across the UT Wasatch and farther east
into the Colorado San Juans and northern New Mexico San Juans and
then Sangre DeCristo ranges.  Higher accumulations are expected in
the southern CO and northern NM ranges due to longer duration of
snow.
Multi-day totals should be in the 1-2 foot ranges in the San Juand
Mountains.

WPC probabilities for the Day 3 period (ending 12Z Friday) show a
Moderate Risk for 4-inches or more across much of this area, with
a Moderate Risk for 8-inches or more across the San Juans in
southwest Colorado.

...Day 1 Southeast CO and Eastern NM...

Northeasterly flow behind the front pushing south through the
Rockies and High Plains will support accumulating snows along the
the Sangre de Cristo Mountains, with WPC probabilities indicating
a Moderate to High Risk for amounts of 4-inches or more across
portions of the Sangre de Cristos Mountains tonight, with the
event ending as a 700 mb ridge builds into the areas Wed with
drying aloft.

...Northeast Days 2/3...

As a northern stream trough progresses east across the Great
Lakes,
mid level warm/moist advection should result in light snow in
northern New England, focused on the ranges of western Maine.  The
southern stream portion of the trough helps initiate coastal
cyclogenesis in the mid Atlantic, but most of the coastal mid
Atlantic to northeast is too warm for snow.

As the southern stream low moves north on Friday, snow is possible
west of the 850 mb low track as it moves north across New England,
placing a threat for several inches of snow in the NY Adirondacks.
 The latest WPC probabilities show the greatest chance for
significant snows centering over northern New England, with a
Moderate Risk for accumulations of the 4-inches or more over
western Maine. 

The probability of significant freezing rain is less than 10
percent.

Petersen