094
FXUS01 KWBC 212000
PMDSPD

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
259 PM EST Thu Nov 21 2024

Valid 00Z Fri Nov 22 2024 - 00Z Sun Nov 24 2024

...Strong atmospheric river continues to impact northern
California with heavy rain and life-threatening flooding through
Friday...

...Developing storm system forecast to bring another round of
gusty winds to the Pacific Northwest on Friday with heavy mountain
snow spreading toward the northern Rockies this weekend...

...Unsettled weather expected across much of the Northeast and
Great Lakes over the next few days, including the likelihood of
heavy snow in the central Appalachians and higher elevations of
northeastern Pennsylvania and southern New York...

The big weather story is the heavy rain and flood threat in the
Pacific Northwest into early Saturday, though the greatest risk
for flooding is ongoing today, Thursday Nov 21st, with the peak of
the atmospheric river transport into southern Oregon and northern
California.  Several inches of rainfall are still possible, around
5-7 inches remain possible over 48 hours with isolated areas in
terrain to see 10 + inches of rain. Northern California is under a
High Risk for Excessive Rainfall and a Moderate Risk goes
northward into southern Oregon. For Friday, the atmospheric river
will be waning, but the atmosphere may still drop a couple of more
inches of rain onto saturated soils. Therefore, most of the
coastal plain from northern California to southern Oregon remain
under a Slight Risk for Excessive Rainfall. The Sierra Nevada
mountain range will be under a Moderate Risk for Excessive
Rainfall with some rain totals greater than 3+ locally on Friday;
additionally, snow levels will be high as warm advection moves in
so areas of higher elevation may see heavy rain as well on top of
snow pack.

The coastal plains and areas of higher elevation in the Pacific
Northwest will continue to face hazardous coastal erosion and
strong winds as another strong area of low pressure develops
offshore. High Wind Warnings are up through Friday morning and the
forecast calls for winds in the 45-65 mph range. Power outages are
possible and unsecured items may get blown over. Then, states in
the northern Rockies like Montana and Idaho and the Sierra Nevada
in California will have the chance for heavy snowfall Friday into
Saturday as the moisture plume begins to advance inland over the
Northwest.

November snowfall is also in the forecast for parts of the
Northeast and Great Lakes thanks to a potent upper-level low
swinging over the region. At the surface, a compact area of low
pressure is currently looping around the Great Lakes with an
eventual southward trajectory over the northern Ohio Valley. Some
light to moderate snow is ongoing this afternoon across the Ohio
and Tennessee River Valleys as far south as Kentucky. The
combination of cold surface temperatues and moisture from the low
pressure will then maximize snowfall totals in the central
Appalachians where over a foot of snowfall is more than possible,
and a Winter Storm Warning is active over terrain in West Virginia
for blowing snow and reduced visibility, winds of 25-45 mph, and
possible power outages from wet snow. A separate area of low
pressure developing near Long Island today is also expected to
track in a looping orientation across the Northeast through
Friday, while also producing periods of heavy snow in areas of
higher terrain in the Northeast and Mid-Atlantic.The greatest
chances for at least 6 inches of snowfall is found across
northeast Pennsylvania and southern New York, including the Pocono
and Catskill mountains. Locations in the Washington-Philadelphia
metro may also see a snowflake or two, but accumulations chances
are low along the I95 corridor. Coastal areas in the Northeast and
Mid-Atlantic will be rather blustery and raw with rain showers and
temperatures in the 30s and 40s through Saturday, though the
precipitation totals should hover around an inch at the heaviest.

The central and southern U.S. can expect much more tranquil
conditions as high pressure creates a void in the unsettled
weather impacting both the East and West coasts. However, below
average temperatures are forecast from the Mississippi Valley to
the Southeast as breezy northwest flow ushers in a colder airmass.
Freeze warnings are active across areas in the Deep South with
lows dropping near to or below freezing.

Wilder

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