Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
356 PM EDT Thu Sep 16 2021

Valid 00Z Fri Sep 17 2021 - 00Z Sun Sep 19 2021

...Post-Tropical Cyclone Nicholas will continue to bring a threat of
locally heavy rain and flash flooding to portions of the Gulf Coast states
over the next couple of days...

...Severe thunderstorms will be possible late this afternoon and this
evening across Minnesota into southeast South Dakota and parts of
Nebraska...

...First atmospheric river of the season will bring very beneficial and
welcomed rains to drought and wildfire-stricken areas of the Pacific
Northwest going into the weekend...

...Very warm, windy, and dry conditions will maintain a wildfire threat
across many areas of the Intermountain West and the northern High Plains
for the next couple of days...

Post-Tropical Cyclone Nicholas continue to linger over far southern
Louisiana this afternoon and should very slowly move northward over the
next couple of days before then dissipating. The system will continue to
bring areas of locally heavy showers and thunderstorms to portions of the
Gulf Coast states for the next couple of days. This will drive concerns
for some additional flash flooding, and the Weather Prediction Center has
depicted a Slight Risk of excessive rainfall for the central Gulf Coast
region stretching from southeast Louisiana east to the western Florida
Panhandle.

Meanwhile, a cold front currently settling southeast across the central
and northern Plains and adjacent areas of the upper Midwest will bring
scattered thunderstorms late this afternoon and evening across this
region, and there will be a threat for some of these thunderstorms to be
severe. In fact, the Storm Prediction Center has depicted a Slight Risk of
severe weather going into the evening hours across Minnesota, southeast
South Dakota, and parts of Nebraska with concerns for supercell
thunderstorms that will be capable of producing large hail, damaging
winds, and a few tornadoes. As the front moves through the Great Lakes
region on Friday and the Ohio Valley early this weekend, there will be
additional scattered areas of showers and thunderstorms associated with
it, but severe weather is generally not anticipated across these areas at
this time.

A well-defined atmospheric river associated with a strong low pressure
system advancing through the Gulf of Alaska will begin impacting the
Pacific Northwest by early Friday morning and will continue doing so
through the weekend. This is the first atmospheric river of the season and
it is expected to bring locally several inches to the coastal ranges of
Washington and Oregon, and also interior areas of the Cascades. Rain
should advance down into at least northern California including the
northern Sierra-Nevada by late in the weekend. This will be very
beneficial and welcomed rain given the current widespread drought
conditions and ongoing wildfire activity.

This system will move into the Rockies by Sunday and much colder
temperatures will settle in behind the frontal passage across the
Northwest which will yield temperatures of as much as 15 to 20 degrees
below average for this time of the year by the end of the weekend.
Conversely, the temperatures out ahead of the cold front will be quite
warm and this will result in a large area of the central and northern High
Plains seeing temperatures at least 15 to 20 degree above average. The
very warm, windy and dry conditions expected ahead of the cold front will
also yield an elevated threat of wildfire activity from areas of the
Intermountain West east into the northern High Plains, and there are
currently Red Flag Warnings in effect to address the wildfire concerns
over the next couple of days.

Orrison

Graphics are available at www.wpc.ncep.noaa.gov/basicwx/basicwx ndfd.php