Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
330 PM EDT Fri Sep 17 2021

Valid 00Z Sat Sep 18 2021 - 00Z Mon Sep 20 2021

...Post-Tropical Cyclone Nicholas is gradually dissipating but will still
bring pockets of locally heavy rain and flash flooding to portions of the
Gulf Coast states this weekend...

...A strong cold front and accompanying atmospheric river will bring windy
conditions and heavy rains to the Northwest tonight through the weekend...

...Very warm, windy, and dry conditions will support widespread elevated
to critical fire weather conditions from the Great Basin to the northern
High Plains through Saturday...

Post-Tropical Cyclone Nicholas will continue to slowly drift north and
weaken over the lower Mississippi Valley over the day or so and should
dissipate on Saturday. However, there will still be additional periods of
showers and thunderstorms that will produce locally heavy rainfall along
the central Gulf Coast. Flash flooding impacts, especially in urban areas,
are possible across this area. Even as the system dissipates, ample
moisture will remain in place through the weekend across much of the
South, and this will support scattered areas of showers and thunderstorms
area wide through the weekend.

Wet weather is also expected for the Northwest as a strong cold front and
an accompanying plume of deep moisture associated with an atmospheric
river gradually crosses the region tonight through the weekend. Locally
strong winds and heavy rain will overspread the coastal ranges of
Washington and Oregon, and the interior high terrain of the Cascades. Rain
should advance down into at least northern California including the
northern Sierra-Nevada by late in the weekend and spread well inland into
the northern Rockies as well. Some of the higher peaks of the northern
Rockies and the northern Cascades by late in the weekend will also see
sufficient cold air arriving behind the cold front for some of the rain to
mix with or change to snow. Given that this is the first atmospheric river
of the season, the rainfall and colder temperatures will generally be
quite beneficial and welcomed given the current widespread drought
conditions and ongoing wildfire activity. Locally as much as 2 to 4 inches
of rain is expected with the highest amounts over the coastal ranges of
the Pacific Northwest and into the Cascades. However, some of this heavier
rainfall may be enough to result in concerns for some localized flash
flooding and debris flow activity around some of the burn scar locations.

Ahead of the system, windy, dry conditions and above-normal temperatures
are expected to support widespread elevated to critical fire weather
concerns across portions of the Great Basin, northern Sierra-Nevada,
northern Rockies, and the northern High Plains through Saturday. As a
result, Red Flag Warnings are in effect for much of this region. Some
temperatures are expected to surge well into the 90s, more than 20 degrees
above normal, across portions of the northern High Plains on Saturday.

Orrison

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