Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
347 PM EDT Fri Aug 19 2022

Valid 00Z Sat Aug 20 2022 - 00Z Mon Aug 22 2022

...Significant heavy rainfall event may lead to major flash flood impacts
in the Southwest...

...More heat expected across interior California and the Pacific
Northwest...

...Thunderstorms could become severe over the Midwest today and
thunderstorms and possible flooding rains will spread across the
South/Southeast and then up the Mid-Atlantic by the weekend...

Much of southern Arizona and New Mexico could have prolific rainfall and
widespread significant flash flooding conditions into the weekend as a
mid-level low and anomalously high moisture associated with a remnant
tropical wave help to enhance storm development associated with an already
very active monsoon season. WPC has a Moderate Risk for excessive rainfall
covering southeast Arizona and southwest/central New Mexico, Slight Risk
spanning from western Arizona to the Texas panhandle and Marginally
encompassing those areas and into the Four Corners/Rockies region. Areal
average rainfall totals of 2-3 inches, with locally higher amounts
approaching 5-7 inches, may lead to numerous instances of flash flooding.
Urban locations in addition to areas of complex terrain, slot canyons,
arroyos, and burn scars are especially vulnerable for flash flooding and
can quickly turn into very dangerous situations.

The focus of the heavy rainfall is expected to shift eastward into the
Southern Plains and persist in proximity to a wavy, stationary front
stretching from the Southeast into the Southern Plains. Several inches of
rain are forecast along a nearly west-east axis from the Texas Panhandle
to the Gulf states, with the heaviest amounts focusing over northeast
Texas, southern Oklahoma, southern Arkansas and northern Louisiana. Much
of this part of the country has had drought conditions, but multiple days
of moderate to excessive rainfall may quickly lead to areas of flooding.
WPC parts of Southern Plains covered by a Slight Risk for Sunday into
Monday. Further north, widespread showers and thunderstorms will continue
along a frontal system moving from the Northern Plains into the Midwest
into the weekend. Instability associated with an upper low rotating across
the northern Plains toward the Midwest could trigger severe thunderstorms
later today into tonight from Iowa into northern Missouri and western
Illinois.  This system will likely trigger additional strong to severe
thunderstorms as it approaches the Great Lakes later Saturday into Sunday
morning.

The heatwave will persist over California and the Pacific Northwest.
Numerous heat-related advisories are in place as temperatures are forecast
to reach into the upper 90s to low 100s today for portions of the interior
Pacific Northwest and northern Great Basin. Some moderating of the daily
temperatures will occur by Saturday with the approaching upper-level, with
a few degrees cool down expected. The central valleys of California, the
heat is forecast to peak on Saturday where afternoon temperatures are
expected to reach into the low to mid-100s. In contrast, much of the
Southwest, Great Basin and Southern Rockies will be well below normal due
to the extensive cloud cover and prolonged rainfall. Daily maximum
temperatures will stay in the 70s to lower 80s. Below normal highs are
also forecast for the Southeast (low to mid-80s) and for the Northern
Plains (low to mid-70s) under the upper low, with temperatures increasing
a few degrees closer to normal Saturday. Hotter temperatures in the upper
80s to around 90 degrees will return to the Mid-Atlantic and New England
with otherwise tranquil conditions expected into the weekend.

Campbell


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