Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
441 AM EDT Sat Aug 20 2022

Valid 12Z Sat Aug 20 2022 - 12Z Mon Aug 22 2022

...A heavy rainfall and flash flooding event moving across Arizona and New
Mexico today is forecast to shift eastward into northern Texas Sunday and
Monday...

...Potential Tropical Cyclone Four is forecast to reach southern Texas as
a tropical storm with heavy rain and some squalls later on Sunday...

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

...Thunderstorms moving across the Midwest could be strong today; some
strong thunderstorms are also possible on Sunday as they move across the
Mid-Atlantic on Sunday...

The stage is set for southern Arizona and New Mexico to potentially
receive prolific rainfall and widespread flash flooding today as a
mid-level low and anomalously high moisture associated with a remnant
tropical wave trigger heavy rain and thunderstorms with an ongoing 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.

Meanwhile, Potntial Tropical Cyclone Four (PTC-4) currently over the
southwestern Gulf of Mexico is forecast to reach southern Texas as a
tropical storm on Sunday.  This system is adding uncertainty and
complexity to the forecast across Texas for the next couple of days. 
Areas of heavy rain and some squalls are expected to move into southern
Texas on Sunday as the system arrives.  Tropical moisture associated with
the system could potential be directed farther north and interact with the
front across northern Texas to prolong the heavy rain threat there.

From later today into Sunday, the focus of the heavy rainfall is expected
to shift eastward into the Southern Plains where a wavy stationary front
stretches from the Southern Plains to the Southeast. Several inches of
rain are forecast along a nearly west-east axis from the Texas Panhandle
eastward to northern Louisiana. Much of this part of the country has had
drought conditions, but multiple days of moderate to excessive rainfall
with potential interaction with tropical moisture from PTC-4 may quickly
lead to areas of flooding. WPC continues to highlight parts of Southern
Plains with a Slight Risk of excessive rainfall from Sunday into Monday.
Further north across the Midwest, widespread showers and possibly strong
thunderstorms are expected to form ahead of an upper low interacting with
a front today.  The showers/thunderstorms are expected to impact the Ohio
Valley on Sunday.  Meanwhile, increasing southwesterly flow will expand
the area of showers and storms across the Deep South on Sunday before
spreading up the East Coast on Monday.  Some storng thunderstorms are also
possibly near the Mid-Atlantic coast later on Sunday, and they could focus
farther north across the northern Mid-Atlantic later on Monday.

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 is expected today with the approaching upper-level trough. 
Meanwhile over the central valleys of California, the heat is forecast to
peak today with afternoon temperatures possibly near 110 degrees at the
hotest locations. 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 across
the Mid-Atlantic and New England this weekend will be followed by clouds
and precipitation approaching from the south on Monday.

Kong/Campbell/Putnum


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