Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
301 PM EST Thu Dec 23 2021

Valid 00Z Fri Dec 24 2021 - 00Z Sun Dec 26 2021

...Series of storm systems to bring heavy mountain snow, moderate lowland
snow, and coastal heavy rain to the western U.S. into the Holiday
weekend...

...Anomalous, record-breaking warmth will continue to spread across most
of the eastern half of the country...

...Scattered rain showers and a wintry mix forecast along a frontal system
moving northward across the Great Lakes and Northeast...


The focus for the short-range forecast period (Thursday afternoon through
Saturday) will be on a series of storm systems sweeping through the
western United States, with impacts enhanced by waves of increased
moisture due to an Atmospheric River. Significant, heavy mountain snow is
forecast from the Sierra Nevada in California north to the Cascades in the
Pacific Northwest. Snow totals will likely exceed a foot through the end
of the forecast period Saturday evening, with several feet possible for
northern portions of the Sierra Nevada. Meanwhile, each system will bring
in cooler and cooler air across the the Northwest, lowering snow levels
later in the forecast period to sea level. Snow showers and the potential
for light accumulations will begin by Saturday from Seattle to Portland.
High temperatures will drop down to the 30s for most locations across the
Northwest. In addition to snow, heavy rain and the potential for flooding
will continue for Southern California as waves of moisture overspread the
region due to the Atmospheric River. A Slight Risk of excessive rainfall
remains in effect through Friday morning for southern portions of the Los
Angeles metro area and the the northern Peninsular Mountains, with a
broader, Marginal Risk continuing north up the coast to the Bay Area. The
threat for a couple inches of heavy rain will continue through this
evening, with the highest flood threat concentrated along burn scars for
both the Peninsular and Transverse Mountains surrounding metro Los
Angeles. The heavy rain threat spreads southward on Friday, with a Slight
Risk of Excessive Rainfall in effect from the Peninsular Mountains and the
southern Inland Empire south across the greater San Diego area. Another 1
to 3 inches of rain is forecast, with rain rates of 0.5 inches per hour
possible. The flood threat will continue to remain concentrated across
burn scars. 

In contrast to the West, large-scale ridging will increase over the
eastern half of the country with conditions trending warmer and drier into
the Holiday Weekend. Daily high temperatures will be well above normal for
most, with near-record and record-breaking highs forecast from the Midwest
to the Southern Plains. High temperatures Friday will range from the 40s
and 50s from the Midwest to the Mid-Atlantic; the 50s and 60s for the
Central Plains, Ohio Valley, and Southeast; and the 70s and 80s for the
Southern Plains. Highs in northwest Texas may even approach 90 degrees. A
cold front will move south through the Midwest and northern portions of
the Southern Plains on Saturday, dropping forecast high temperatures by
about 10 degrees compared to Friday, though this will still be well above
normal. The warm temperatures, along with dry, windy conditions has led to
an Elevated Risk of fire weather issued by the Storm Prediction Center for
the Southern High Plains through Friday. One exception to this anomalous
warmth will be in the Northern Plains as a cold front ushers in frigid air
from Canada and then remains stalled south of the region. Highs on Friday
for much of Montana will be in the teens, with single digit highs forecast
for both Montana and North Dakota on Saturday.

Both rain showers and a wintry mix will likely continue from the Great
Lakes to the Northeast as a warm front moves northward across the region.
Snow showers are likely north of the front from the Great Lakes through
New York overnight Thursday. Light rain showers are forecast to move east
from the Great Lakes on Friday to the Mid-Atlantic Saturday as the warm
front moves northward. A wintry mix is forecast north of the boundary for
the northern Great Lakes, upstate New York, and New England.

Putnam


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