Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
424 AM EDT Mon Mar 18 2019

Valid 12Z Mon Mar 18 2019 - 12Z Thu Mar 21 2019

...Western U.S....

The ongoing quiet pattern with respect to precipitation is
expected to continue for another day before becoming a little more
active beginning Tuesday as a well-defined shortwave drops south
into the central Plains.  Models show a strong upper high shifting
east across western Canada and the northwestern U.S. with an
amplifying shortwave to its east dropping south.  This system is
expected to descend from the northern into the central Plains late
Tuesday into Wednesday.  This will send a weak surface wave moving
east from the High Plains toward the lower Missouri valley with a
trailing cold front pushing south through the Rockies.  Upslope
flow will encourage accumulating snows along the Colorado Front
Range south into the Sangre de Cristos and farther west into the
San Juans mainly east of the Divide.  Local amounts of 4-inches or
more are possible, with WPC probabilities indicating a Moderate
Risk on Day 2 (ending 12Z Wednesday) across portions of the higher
terrain. 

Meanwhile, farther to the west a negatively-titled upper level
trough is expected to move into California, supporting a Moderate
Risk for accumulations of 4-inches or more on Day 2 along the
Sierra, mainly for the western slopes above 7000 ft.  Accumulating
snows are expected to extend farther east on Day 3 as an upper low
closes off within the base of the trough and moves east across
California.  Additional snows are likely along the Sierra, with
WPC probabilities indicating a Moderate Risk for accumulations of
4-inches or more, with a Slight Risk for amounts reaching 8-inches
or more above 7000 ft during the Day 3 period (ending 12Z
Thursday).  Favorable upper jet dynamics may support locally heavy
totals farther east across the central Nevada southern Utah ranges
into the central Rockies.  WPC probabilities suggest some of the
heaviest amounts will occur along the southern facing slopes of
the San Juans in southwest Colorado, where a Moderate Risk for
8-inches and Slight Risk for a foot or more is indicated on Day 3.

Pereira