Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
333 AM EDT Mon Aug 21 2023

Valid 12Z Mon Aug 21 2023 - 12Z Wed Aug 23 2023

...Heavy rain, scattered flash flooding, and gusty winds associated with
Hilary continue throughout the Intermountain West today...

...Excessive rainfall threat exists across South Texas on Tuesday...

...About 80 million people under heat alerts as record-breaking heat
continues from the Midwest to Gulf Coast...

After moving inland across Southern California late Sunday, moisture
associated with Hilary is forecast to continue streaming northward through
the Intermountain West today. The anomalous moisture fetch is being aided
by upper-level troughing across the West Coast and a strong ridge in the
middle of the country. Areas of lingering showers and thunderstorms may
lead to additional areas of flash flooding across the high terrain of the
Sierra and throughout much of Nevada. Farther north, widespread moderate
to locally heavy rain may also create flooding concerns throughout the
northern Great Basin as a nearby frontal boundary provides a focus for
precipitation. A Slight Risk (level 2/4) of Excessive Rainfall remains in
effect across a broad region extending from northwest Montana to southern
Nevada and north-central Arizona. Additionally, gusty winds associated
with a surface low progressing northward could lead to wind gusts up to 70
mph across the higher terrain, passes, and summits of the Intermountain
West. High Wind Warnings extend from the Desert Southwest to southern
Idaho. Additional moisture funneling northward through midweek could lead
to renewed scattered flash flooding concerns across the northern Great
Basin and Utah.

Heavy rain chances also exist across South Texas on Tuesday as a fast
moving tropical disturbance enters the region from the Gulf of Mexico,
which the National Hurricane Center happens to be monitoring for potential
development. Regardless of organization, a few inches of rain within a
short period of time could lead to scattered flash flooding throughout the
region. This has prompted a Slight Risk of Excessive Rainfall to be issued
from Corpus Christi to the U.S.-Mexico border.

Meanwhile, the more widespread weather hazard extending through midweek
involves searing temperatures impacting a majority of the central U.S. and
Gulf Coast. Dangerous heat underneath an extremely potent upper-level
ridge centered over the Middle Mississippi Valley is forecast to stretch
from parts of the Upper Midwest to the Gulf Coast. Highs into the
upper-90s and triple digits will be easy to come by over the next several
days, with heat indices into the 110s when taking into account the
humidity. Although the middle to end of August can be notoriously hot, the
forecast temperature readings for these areas are expected to break
numerous daily and potentially monthly records. Highs over Iowa and
neighboring states could reach as high as 20 degrees above average when
compared to climatology. The prolonged nature of the heat wave combined
with very warm overnight temperatures will limit relief from the
oppressive daytime heat and compound overall heat impacts. Residents and
visitors are advised to follow proper heat safety, which includes staying
hydrated and avoid extended periods of time outdoors. Excessive Heat
Warnings/Watches and Heat Advisories currently include 18 states from
Louisiana to Minnesota, which includes approximately 80 million people.
Steamy temperatures into the Southeast and Mid-Atlantic are also forecast,
with temperatures in the Mid-Atlantic quickly cooling behind a cold front
on Tuesday.

Elsewhere, on the periphery of the strong upper-level ridge, isolated
severe thunderstorms are possible across the Upper Midwest and Great Lakes
through Tuesday. For the Pacific Northwest, dense wildfire smoke over the
region is expected to linger for at least an additional day, prompting
widespread Air Quality Alerts.

Snell


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