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

Valid 00Z Tue Aug 22 2023 - 00Z Thu Aug 24 2023

...There is a Slight of excessive rainfall over parts of the Western U. S.
on Monday and Tuesday and southern Texas on Tuesday...

...There are Air Quality Warnings over the parts of the Pacific Northwest,
Central Rockies, and Mid-Atlantic...

...Excessive Heat Warnings and Advisories from parts of the Plains, the
Mississippi Valley, and Central/Western Gulf Coast...

A plume of moisture associated with what was once Hilary will produce
showers and thunderstorms over parts of California, the Great Basin,
Southwest, Pacific Northwest, Northern Intermountain Region, and Northern
Rockies. Therefore, the WPC has issued a Slight Risk of excessive rainfall
over parts of California, Great Basin, Southwest, Pacific Northwest,
Northern Intermountain Region, and Northern Rockies through Tuesday
morning. The associated heavy rain will create mainly localized areas of
flash flooding, with urban areas, roads, small streams, and burn scars the
most vulnerable.

In addition, the associated moisture plume will aid in producing strong to
severe thunderstorms over parts of the Southwest, Great Basin, and
Northern. Therefore, the SPC has issued a Marginal Risk of severe
thunderstorms over parts of the Southwest, Great Basin, and Northern
Rockies through Tuesday morning. The hazards associated with these
thunderstorms are frequent lightning, severe thunderstorm wind gusts,
minor threat of hail, and a minimal threat of tornadoes.

The threat of excessive rainfall continues on Tuesday as showers and
thunderstorms with heavy rain develop over parts of the Great Basin,
Southwest, and Northern Intermountain Region. Therefore, the WPC has
issued a Slight Risk of excessive rainfall with these thunderstorms over
two regions, the first area over parts of the Northern Intermountain
Region and the second over parts of the Great Basin, on Tuesday into
Wednesday morning. The associated heavy rain will create mainly localized
areas of flash flooding, with urban areas, roads, small streams, and burn
scars the most vulnerable.

In addition, on Tuesday, Potential Tropical Cyclone NINE over the northern
Gulf of Mexico will stream moisture into the Western Gulf Coast, producing
showers and thunderstorms with heavy rain. Therefore, the WPC has issued a
Slight Risk of excessive rainfall with these thunderstorms over parts of
the Western Gulf Coast (southern Texas) on Tuesday. The associated heavy
rain will create mainly localized areas of flash flooding, with urban
areas, roads, and small streams the most vulnerable.

Elsewhere, a front over the Northeast will settle over the Mid-Atlantic by
Tuesday. The system will produce scattered showers and thunderstorms over
parts of the Northeast on Monday evening. In addition, a wave of low
pressure over the Upper Mississippi Valley will produce scatted showers
and thunderstorms over parts of the Upper Mississippi Valley and Upper
Great Lakes on Tuesday. As the wave moves eastward, showers and
thunderstorms will develop over parts of the Great Lakes/Ohio Valley on
Wednesday. Further, onshore flow off the Atlantic will continue to produce
showers and thunderstorms over the southern tip of Florida through
Wednesday.

Moreover, wildfire smoke over parts of the Pacific Northwest, Central
Rockies, and Mid-Atlantic has prompted Air Quality Alerts over parts of
the Pacific Northwest Central Rockies and Mid-Atlantic on Monday evening
into Tuesday morning.

Meanwhile, an upper-level high over the Central Plains/Middle Mississippi
Valley will create oppressive daytime heat, limited overnight cooling,
which will also contribute to the effects of heat, prompting Excessive
Heat Warnings and Heat Advisories over portions of the Central/Southern
Plains, the Upper/Middle/Lower Mississippi Valley, Central/Western Gulf
Coast.

In addition, extremely dangerous heat will expand and intensify across
much of the central U.S., with numerous daily high-temperature records
expected, especially in Texas and the Lower Mississippi Valley. Parts of
the Upper and Middle Mississippi Valley and Central Plains will experience
heat index readings near or above record levels this afternoon through
Thursday this week. The excessive heat threat will begin to retreat from
the Upper and Middle Mississippi Valley later this week before settling
over the Gulf Coast this weekend. Take the heat seriously and avoid
extended time outdoors. Temperatures and heat indices will reach levels
that would pose a health risk and be potentially deadly to anyone without
effective cooling and/or adequate hydration.


Ziegenfelder


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