Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
424 PM EDT Sun Mar 10 2019

Valid 00Z Mon Mar 11 2019 - 00Z Thu Mar 14 2019


...Southwest to the Southern and Central Rockies...

An upper low closing off along the California coast is forecast to
drop farther south before turning east into the northern Baja
California Peninsula Monday night.  A strong upper level jet
extending from the base of the trough will help support some
orographically focused heavy snows along the south faces of the
San Juans on Monday.  Elsewhere however, limited moisture will
hamper the potential for more widespread heavy snows across the
region.

Monday night into Tuesday, models continue to show a well-defined
shortwave digging south of the low as it moves farther east along
the U.S.-Mexico -- amplifying the flow and increasing moisture
advection into the Southwest.  This will help raise the potential
for locally heavy snows across central Arizona along the Mogollon
Rim into the White Mountains, with additional heavy amounts likely
along the San Juans.

Snows will continue into Wednesday as the low begins to lift to
the northeast across the southern Rockies and ahead of a northern
stream trough digging across the Great Basin into the Four Corners
region.

...Pacific Northwest to the Northern Rockies...

Mountain snows are expected to return to the Northwest by early
Tuesday as an amplifying shortwave and its associated cold front
sweep into the region.  This will bring some locally heavy
accumulations to the northern Cascades, with generally lighter
amounts spreading across the Blue Mountains and northern Rockies
on Tuesday. As cold air filters in behind the front, snow levels
are expected to decrease but the latest guidance shows rain for
the lowlands of western Washington.  Models show this to be a
progressive system, with drier weather expected for the Northwest
on Wednesday.  However snows are forecast to continue for portions
of the northern Rockies, with generally light to moderate
accumulations expected.

...Central Rockies and Plains...

As the previously noted low in the Southwest begins to lift out
across the southern Rockies and into the Plains, heavy snows are
forecast to develop and spread east of the central Rockies into
the High Plains on Wednesday.  Models show the low assuming a
negative tilt, lifting northeast across New Mexico Wednesday night
ahead of the northern stream trough digging south into the Great
Basin.  As the low lifts into the central Plains, models are
showing a strong signal for developing heavy snows, supported by
strong upper dynamics, coupled with low-mid level frontogenesis
north and west of the low.  Strong cold air advection will support
rain changing to snow over the Plains.  With the NAM, GFS and EC
all in fairly good agreement with this system, the latest WPC
probabilities show a Moderate Risk for accumulations of 8-inches
or more during the Day 3 period (ending 00Z Thu) from southeast
Wyoming and northeast Colorado into the southern Nebraska
Panhandle.  A Slight Risk for a foot or more is indicated across
this same area as well.

Pereira