147
FXUS63 KLSX 211729
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
1229 PM CDT Tue Jul 21 2026

.KEY MESSAGES...

- A cold front will bring a slight chance for thunderstorms this
  afternoon over southwest Illinois and southeast Missouri. The
  strongest storms could produce strong wind gusts.

- Cooler and less humid air will move into the area behind the
  cold front, with highs only in the 70s and 80s from Wednesday
  through Friday.

&&

.SHORT TERM /THROUGH WEDNESDAY/...
Issued at 326 AM CDT Tue Jul 21 2026

A complex of thunderstorms are moving south across northern Missouri
early this morning ahead of a cold front that currently extends
across Iowa and Nebraska.  This complex is expected to begin to
diminish the next few hours as the low level jet veers to the east.
There is some potential that this complex will hold together this
morning and provide some early relief to the heat over parts of the
advisory area.  At this point I plan on holding on to the entire
area as high temperatures over the southern half the CWA should
still climb into the low-mid 90s.  Forecast guidance does not show
the dewpoints behind the front falling off into the 60s until this
afternoon so we will still see heat index values rising into the 100-
105+ range from late this morning into this afternoon, particularly
over parts of southeast Missouri into southwest Illinois.

There will be some potential for redevelopment of thunderstorms late
this morning and this afternoon along front.  There will be limited
synoptic lift and convergence along the front, so have kept only a
20% chance over southwest Illinois and southeast Missouri.  Couldn`t
rule out the potential for some strong wind gusts with these storms
based on the RAP soundings at SLO and FAM.  Once the front clears
the area, tonight and Tuesday looks dry.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Issued at 326 AM CDT Tue Jul 21 2026

Dry weather is expected to continue through Thursday the LREF is
showing a upper high building over the southern Plains.  The LREF is
still showing a trough dropping southeast across the Midwest late in
the week with a 40-60% chance of showers and thunderstorms on
Friday.   This is at the same time when the ECWMF/GFS is showing
high PWATS coupled with a strong LLJ and WPC is highlighting central
MO with a slight risk for excessive rainfall, so we will need
to keep an eye out for locally heavy rainfall. Otherwise, the
LREF is showing a ridge building over the central CONUS with the
NBM keeping the upcoming weekend dry.

The relief from the warm weather is expected to continue through
late week with high temperatures 5-10 degrees below normal through
Friday.  Highs will rise back above normal over the weekend as 850mb
temperatures climb back above +20C.

&&

.AVIATION /18Z TAFS THROUGH 00Z THURSDAY/...
Issued at 1225 PM CDT Tue Jul 21 2026

A cold front is moving south across the eastern Ozarks this
afternoon. There is a chance for scattered thunderstorms in
southeast Missouri along and ahead of the front. Any storms that
develop will be capable of producing 40-50kt wind gusts and IFR
visibilities in heavy downpours. Otherwise, VFR flight
conditions and northerly flow is expected to prevail across the
area as high pressure builds in behind the cold front.

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Heat Advisory until 7 PM CDT this evening for MOZ041-047>051-
     059>065-072>075-084-085-099.
IL...Heat Advisory until 7 PM CDT this evening for ILZ069-074-079-
     100>102.

&&

$$

SHORT TERM...Britt
LONG TERM...Britt
AVIATION...Carney