Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
331 PM EDT Wed Aug 23 2023

Valid 00Z Thu Aug 24 2023 - 00Z Sat Aug 26 2023

...Record heat to continue through this week for the mid section of the
nation, but relief is in sight for some by the weekend...

...Heavy rains and localized flash flooding possible from the Southwest
into the southern Great Basin and Central Rockies, and from the eastern
Great Lakes into the Mid-Atlantic and Northeast...

The anomalously strong mid to upper level ridge that has been driving the
most recent episode of the persistent summer 2023 U.S. heat wave will
continue to produce record heat and heat index values over the next few
days across large portions of the nation from the Mid-West, south through
the Mississippi Valley, across eastern portions of the Plains and into the
central Gulf Coast.  Across these regions triple digit high temperatures
are likely over the next two days.  When combined with high dew point
values from the mid 70s to lower 80s, maximum heat index values of 110 to
120 are likely.  Across these areas, excessive heat warnings and heat
advisories are in effect for nearly 120 million people.  The good news is
that there are changes on the horizon, with cooler temperatures likely to
begin to push from north to south by the end of this week into this
weekend as the mid to upper level ridge begins to weaken and a cold front
pushes south.  Areas of the Upper Mississippi Valley into the Mid-West
will be first to see cooler temperatures by Friday, with the big cities of
Minneapolis and Chicago seeing an end to the heat wave. By the weekend the
cooler temperatures will make it into Kansas City and St. Louis, but heat
and high heat indices will continue farther to the south across the
Southern Plains, Lower Mississippi Valley, Gulf Coast and Southeast
through the weekend.

Around the peripheries of this heat dome, active showers and thunderstorms
are possible from the Southwest into portions of the Great Basin and
Central Rockies.  Across these regions, above average moisture values from
the remnants of Harold,that made landfall on the Texas Gulf coast on
Tuesday, will rotate clockwise around the strong mid to upper level high
over the central U.S. and into portions of the Southwest, southern Great
Basin and Central Rockies region.  These above average moisture values
will support the potential for heavy rains and localized flash flooding
over the next two days.

Active showers and thunderstorms are also likely on the northern and
northeastern peripheries of the strong mid U.S. upper ridge from the
eastern Great Lakes, southeastward into the Mid-Atlantic and into the
Northeast.  Periods of active showers and thunderstorms are possible
across these areas beginning Wednesday night and continuing into Friday. 
This will support the potential for locally heavy rains and isolated flash
flooding across these areas.

In addition to the heavy rain threat over the lower Lakes into the
Mid-Atlantic, there will also be the potential for severe thunderstorms
over the next two days across these areas, with high winds and large hail
the greatest threat.

Oravec

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