Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
401 AM EDT Thu Oct 21 2021

Valid 12Z Thu Oct 21 2021 - 12Z Sat Oct 23 2021

...Powerful Pacific storm to deliver heavy rain and gusty winds to the
Pacific Northwest, Slight Risks for Excessive Rainfall in Northern
California and far southwestern Oregon today...

...Severe thunderstorms possible in some eastern regions due to a low
pressure system tracking through the Great Lakes today; scattered
thunderstorms also possible in portions of the Southern Plains today and
Friday...

...Abnormally warm conditions in the Rockies and High Plains; warm day
along the East Coast today gives way to cooler temps by week's end; cooler
in the Midwest and along the West Coast...

A rapidly deepening cyclone in the northeast Pacific responsible for the
development of an atmospheric river aimed at the West Coast and coastal
British Columbia is set to produce unsettled weather that will arrive in
the Pacific Northwest later today. The bouts of rain are a sight for sore
eyes in the drought stricken areas of the Northwest with beneficial
rainfall totals ranging between 2 to 5 inches in the higher elevations of
Northern California and southwestern Oregon. However, locally heavy
rainfall rates atop burn scarred areas could lead to flash flooding, rapid
runoff, and debris flows in these locations. Slight Risks for Excessive
Rainfall have been issued for a handful of areas in Northern California
and far southwestern Oregon along with Flash Flood Watches in parts of the
northern Sierra Nevada. As the upper low associated with this Pacific
storm moves ashore Thursday night, snow levels will drop throughout the
night and into Friday as it also aids in pushing precipitation farther
inland. Despite the falling snow levels, snow totals will generally be
light with the lone exceptions being the highest peaks of mountain ranges
that include the northern Sierra Nevada, the Shastas, and the Cascades. As
the storm system pushes into the northern Rockies and gradually weakens,
the next Pacific low pressure system is hot on its heels as it ushers in
more unsettled weather into the Pacific Northwest on Saturday.

Meanwhile, a vigorous upper level disturbance in the Midwest early this
morning will track east underneath a large upper low spinning over
northern Ontario. The surface low is forecast to strengthen as it tracks
through the Great Lakes and its associated cold front sweeps across the
Ohio Valley and Mid-South. Thunderstorms firing out ahead of the cold
front could be severe, prompting the Storm Prediction Center to issue a
Marginal risk for severe weather from the eastern Great Lakes on south
into the Tennessee Valley. Severe storms are also possible in West Texas
where a modestly unstable air-mass will be in place. After spotty showers
and thunderstorms track through the Northeast and Mid-Atlantic Thursday
night, the cold front reaches the East Coast by Friday afternoon. Some
severe storms could occur in eastern North Carolina and South Florida
Friday afternoon. Farther west, a warm front pushing north through the
Southern Plains could trigger hit-or-miss showers and thunderstorms Friday
afternoon and into Friday night.

Temperatures will be warmest in the Intermountain West and Great Plains as
upper level ridging builds aloft downwind of the robust upper trough in
the northeast Pacific. Fridays high temps will be quite warm from the
Southern Plains to the plains of Montana with the hottest temperatures
expected along the Rio Grande River where highs could hit 90 degrees. The
East Coast rebounds to more September-like levels of heat today before the
aforementioned cold front sends a shot or more autumn-like conditions,
currently located in the Midwest, into the Great Lakes and Northeast for
Friday and into the upcoming weekend. Expect the Deep South to remain on
the abnormally warm side through the end of the work-week. Lastly, the
West Coast will contend with persistent cloud cover thanks to the series
of systems causing onshore flow. Temperatures ranging between 5 to 15
degrees cooler than average are expected with the coldest anomalies
focused in Northern California.

Mullinax

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