Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
300 PM EST Thu Nov 11 2021

Valid 00Z Fri Nov 12 2021 - 00Z Sun Nov 14 2021

...Moderate to heavy snow coupled with high winds expected over the
Northern Plains and Upper Midwest through Friday evening; isolated
blizzard conditions possible...

...Flash flooding potential to continue over the Pacific Northwest through
Saturday morning as onslaught of heavy rainfall continues...

...A sweeping cold front will drop temperatures well below normal from the
Plains to the Appalachians...

An occluded low pressure/frontal system centered over the Upper Midwest
will be the focus of a snow storm set to impact the region and the
neighboring Northern Plains through late Friday evening. Cold air
advection to the north/west of the system, an influx of moisture from the
Gulf of Mexico, and deep layer ascent due to coupling with a cut-off low
aloft will all contribute to the development of a favorable environment
for moderate to heavy snowfall. Widespread accumulations of 2-6 inches are
likely, with higher totals of 6-8+ inches expected in northern Minnesota
and along the Canadian border in eastern North Dakota. Winter Weather
Advisories are currently in effect for portions of the Dakotas, Minnesota,
and northern Iowa while Winter Storm Warnings have been issued for
portions of northern Minnesota. In addition to the snow a tight pressure
gradient on the western edge of this system will generate high winds with
gusts reaching 60-70 mph over the Northern Plains, where both High Wind
Warnings and Wind Advisories are in effect. While hazardous enough on
their own, these high winds are forecast to impact some areas where
moderate snowfall rates and accumulations are expected. Due to the
potential for these strong winds to blow snow around and significantly
reduce visibility, a Blizzard Warning has been issued for portions of
northeast South Dakota and west-central Minnesota.

On the warmer eastern edge of this system showers and thunderstorms
focused around and ahead of the trailing cold front will deliver moderate
to heavy rain from the Ohio and Tennessee Valleys to the Eastern Seaboard
through Friday night. The heaviest rainfall is expected over the northern
Mid-Atlantic and Northeast, where high rain rates could lead to isolated
instances of runoff and flash flooding. As such, the Weather Prediction
Center has issued a Marginal Risk of Excessive Rainfall for portions of
the Northeast effective Friday morning through Saturday morning.

Shifting focus out west, onshore moisture flow from a modest atmospheric
river will bring moderate to heavy rainfall to portions of the Pacific
Northwest. Another 2-4 inches of rain have been forecast for the region
over the next 24 hours and rainfall rates over some areas may be as high
as 0.5-0.75 inches per hour. Given the already saturated soils from the
previous days' rain and the concern for the development of rapid run-off
and urban flooding, the Weather Prediction Center has issued a Slight Risk
of Excessive Rainfall for portions of the Pacific Northwest through Friday
morning. Though the onshore moisture flow from the atmospheric river is
expected to begin tapering off on Friday, thus dropping 24 hour rainfall
totals to around 1-2 inches over the region, the potential for high
rainfall rates and associated flooding issues will continue through Friday
afternoon prompting the maintenance of a Marginal Risk of Excessive
Rainfall over the Pacific Northwest through Saturday morning.

In the Central/Southern Plains, dry and breezy conditions coinciding with
low values of relative humidity has prompted the issuance of an Elevated
Risk of fire weather by the Storm Prediction Center through Saturday
morning, as these conditions could allow any fires that ignite to spread
rapidly.

Temperature-wise, daily highs across much of the country are forecast to
sit near or moderately (within 10 degrees) above normal. However, for
those areas that find themselves to the west/southwest of the occluded low
pressure system the opposite holds true. Significant cold air advection
behind the system, aided by the cut off low aloft, will force temperatures
to drop well below normal behind a cold front set to develop across the
central US this evening. On Friday the Central Plains and Middle
Mississippi Valley will be hit the hardest as highs are expected to fall
into the 30s and 40s, around 10 to 15 degrees below normal. As the Plains
warm up on Saturday with the advancement of a warm front through the
region, cooler temperatures are expected to settle into the Tennessee and
Ohio Valleys with the eastward progression of the cold front. With
temperatures sitting 10 to 20 degrees below normal, daily highs in these
areas will be unable to escape the 40s and 50s.

Zavadoff


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