Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
420 AM EDT Tue Mar 21 2023

Valid 12Z Tue Mar 21 2023 - 12Z Thu Mar 23 2023

...Powerful storm system to spread high winds, heavy rain, and heavy
mountain snow to parts of California and the Southwest...

...Widespread rain/heavy mountain snow expected to move across the Great
Basin and the central/southern Rockies through Thursday morning...

...A couple quick rounds of light-to-moderate snowfall are expected across
portions of the northern Plains and Upper Midwest through Thursday
morning...

A low pressure system currently developing rapidly over the Pacific to the
west of California is forecast to deliver quite an impactful weather event
through the southwestern quadrant of the country over the next couple of
days.  The outer edge of the precipitation associated with this system is
already moving onshore across southern California.  Heavy rain and heavy
mountain snow will likely expand through California, the Great Basin
followed by the Four Corners and through the central and southern Rockies
as the system slams onshore and moves across these areas through Thursday
morning.  In addition, potentially damaging wind gusts can accompany the
system, especially when the storm center is forecast to approach and/or
make landfall near San Francisco this evening, as the system possibly
acquires some sub-tropical characteristics near the center under an
anomalously cold upper low over the ocean.  Farther south, a strong
pressure gradient could lead to maximum wind gusts near 75 mph across
southern California.  Meanwhile, a surge of subtropical moisture will
accompany this system and create a ripe environment for heavy rain from
the central coastline to southern California. Heavy rain is likely to lead
to rapid runoff and areas of flooding across southern California, with
isolated flooding instances possible for regions to the north. For the
mountainous terrain of the southern/central Sierra Nevada and Southern
California, heavy snow will be the primary hazard as snowfall
accumulations add up to as much as 3 to 4 feet in spots. This additional
snowfall will lead to difficult travel and could strain infrastructure in
areas still buried under a record-breaking snowpack for the year-to-date.
Impacts are also anticipated to spread farther inland during the second
half of Tuesday across the Southwest, central Great Basin, and
south/central Rockies. Gusty southwesterly winds up to 60 mph are possible
across the Desert Southwest, with heavy rain and localized flash flooding
possible across parts of central Arizona. Elevated terrain from central
Nevada to western Colorado can expect heavy snow to last into Wednesday.
Dangerous to difficult travel is likely, with most mountain ranges
experiencing over a foot of snowfall. Numerous wind, flood, and winter
headlines have been issued for the upcoming storm. Be sure to check with
your local forecast office for details.

Wintry weather will also impact the north-central U.S. through early
Thursday as two separate systems traverse the region. Between Tuesday and
Wednesday morning, a low pressure system is forecast to swing from the
northern Plains to the Upper Great Lakes, with locally heavy snow possible
just to the north from southeast North Dakota to northern Minnesota.
Snowfall amounts up to 7 inches are possible and when combined with areas
of blowing snow, visibility could be reduced and create treacherous
driving conditions. Beginning late Wednesday, the western U.S. system is
forecast to redevelop over the central U.S. where a swath of additional
snowfall from south Dakota to southern Minnesota is expected just to the
south of the first storm. Snowfall totals could add up to over 4 inches.
Farther south and east, scattered showers and thunderstorms are
anticipated to develop along a stationary front Wednesday night across
portions of the Midwest.

Elsewhere, one more chilly morning is expected for the Southeast today
before springlike temperatures migrate eastward from the southern Plains
by midweek. Low temperatures tonight are still likely to dip below
freezing throughout the Tennessee Valley and Southeast. Freeze Warnings
and Frost Advisories have been issued from eastern Mississippi to the
Carolinas in order to highlight the potential for damage to sensitive
vegetation and unprotected outdoor plumbing.  Meanwhile, rain is forecast
to expand eastward across the Ohio Valley and Great Lakes on Wednesday
before reaching New England early Thursday with some wintry precipitation
expected for northern New England.


Kong/Snell


Graphics available at
https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php