Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
354 PM EDT Fri Oct 22 2021

Valid 00Z Sat Oct 23 2021 - 00Z Mon Oct 25 2021

...A parade of Pacific storm systems to produce copious amounts of rain
and isolated heavy mountain snow in the Northwest and California...

...Developing low pressure system in the Central Plains to bring heavy
rain and severe weather to the region over the weekend...

...Above normal temperatures will continue in the Central and Southern
Plains; more seasonal temperatures to return to the Intermountain West and
East Coast; cooler than average temperatures hang over the Midwest and
along the West Coast...

...Elevated fire weather risk issued for portions of the Southern Plains...

A series of Pacific storms moving onshore over northern California and the
Pacific Northwest will serve to continue the recent trend of wet weather
over the regions. As the remaining cold front from yesterday's system
moves further inland an additional 1 to 2 inches of rain are expected to
fall over burn scar affected areas of northern California. Given the
continued potential for rapid runoff and debris flows in these areas a
Marginal Risk of Excessive Rainfall has been maintained for the northern
Sierra Nevada. Continued eastward progression of the frontal boundary will
spread moderate rain and high elevation snow into the Intermountain West
and Northern/Central Rockies overnight. Before the memory of the first
Pacific storm is able to fade the second system is forecast to make its
approach on the West Coast Saturday morning. Relatively weaker than the
previous system, this storm is expected to dissipate quickly after
landfall, but not before bringing an additional 1 to 2 inches of rain and
to northern California and southern Oregon. Due to the numerous burn scars
in these areas as well as the general sensitivity of the soils from the
previous days' rain a Marginal Risk has been maintained on Saturday for
the northern Sierra Nevada and expanded to encompass coastal northern
California and extreme southwestern Oregon. Not to be outdone, the third
and strongest of the forecasted Pacific storms will slam into the West
Coast Sunday morning. Exceptionally high levels of atmospheric moisture
embedded within this system in the form of a very powerful Atmospheric
River are expected to slam into northern California. With snow levels at
the time sitting around 10000-11000 ft, most of the precipitation
associated with this system will fall as rain except for at this highest
mountain peaks. Such an intense influx of moisture will inundate northern
California in as much as 3 to 5+ inches of rain in 24 hours, exacerbating
concerns for flash flooding, rapid runoff, and debris flows. As such, the
Weather Prediction Center has upgraded its Excessive Rainfall Outlook to a
Moderate Risk on Sunday for portions of northern Sierra Nevada, while a
Slight Risk remains in place for the surrounding areas.

Farther east, a developing low pressure system is forecast to bring
showers and thunderstorms to the Central Plains and Middle Mississippi
Valley overnight ahead of a lifting warm front. As the system
progressively deepens on Saturday it's attendant warm front will continue
its northward track and begin encroaching on a quasi-stationary boundary
over Missouri Saturday afternoon. With ample surface instability and
moisture available between these two fronts, any thunderstorms that
develop may become severe. Given the potential for these thunderstorms to
produce damaging wind, large hail, and an isolated tornado or two, the
Storm Prediction Center has issued a Slight Risk of Severe Thunderstorms
for portions of northeastern Kansas and far western Missouri effective
Saturday morning to Sunday morning. Further strengthening of the system
overnight will lead to the continuation of the severe weather threat over
the Middle Mississippi Valley in the form of an Enhanced Risk of Severe
Weather. Forecasted environmental conditions appear favorable for the
development of supercells with the potential to produce damaging wind
gusts, large hail, and tornadoes. In addition to the severe weather
threat, there will also be the risk of flash flooding as heavy rainfall
could lead to accumulations of 2 to 3 inches of rain in a 24 hour period
over portions of the Middle Mississippi Valley, prompting the issuance of
a Slight Risk of Excessive Rainfall for Sunday. Meanwhile, a cold front
passing slowly through the Eastern Seaboard will move offshore overnight
tonight, but not before triggering more showers and thunderstorms over
eastern North Carolina, some of which may become severe with isolated wind
damage and moderate sized hail.

Temperatures will generally remain near or above normal in the
south-central part of the country during the short range period. These
warm temperatures, lack of recent precipitation, and sustained dry and
breezy conditions will support modest priming of grass-based fuels. As
such, the Storm Prediction Center has issued an Elevated Risk of fire
weather for portions of New Mexico through Sunday morning and the northern
Texas Panhandle Saturday morning to Sunday morning. To the north, cold air
ushered in by surface high pressure situated over central Canada and the
Midwest will set the stage for modest temperature drops from the Upper
Midwest to the Northeast. While daily highs will remain generally in the
low to mid 50s, which is just a few degrees below average, some isolated
areas could experience temperature anomalies as large as 10 degrees below
normal. As for the West Coast, persistent cloud cover from the series of
systems moving onshore will keep the region around 10 to 15 degrees cooler
than average for this time of year. However, in areas of higher elevation
such as the Sierra Nevada, temperature departures are expected to be more
extreme at 20 to 25 degrees below normal.

Zavadoff

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