079
FXUS63 KLSX 241055
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
555 AM CDT Fri Jul 24 2026

.KEY MESSAGES...

- Periods of scattered showers and a few thunderstorms are
  expected today through early Saturday, with the primary
  threat being locally heavy rainfall.

- Heat and humidity will lead to dangerous conditions early
  next week. An Extreme Heat Watch is in effect for Sunday
  afternoon through Tuesday evening.

&&

.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 246 AM CDT Fri Jul 24 2026

Broad northwesterly flow extends from the Northern Rockies to the
Eastern Seaboard per current water vapor imagery. Within this flow,
a shortwave is moving through the Central Plains and heading toward
the Middle Mississippi Valley. This shortwave will pass through the
region through the day today into early Saturday, bringing periods
of mainly scattered showers but a few thunderstorms as well.
Instability will be limited through today, increasing gradually
tomorrow but remaining low. Therefore, only occasional, weak
thunderstorms are expected. Even so, with PWAT hovering around 2"
and the warm cloud layer being around 10kft, showers and
thunderstorms will be capable of locally heavy rainfall. Storm
motion will limit residence time for any one location, with
accumulations over an inch being the result of a low chance for
training convection. The 00z HREF and REFS support very isolated
amounts of up to 3-4" of rain mainly along and south of I-70. Given
the low potential and isolated nature of this threat, confidence is
not high enough at this time to warrant a Flood Watch, but we will
continue to monitor the potential.

Thanks to the rainfall and associated cloud cover, temperatures
today will remain unseasonably cool. Most locations will struggle to
break out of the 80s. However, this will be the last day of cooler
conditions, as a ridge will gradually amplify over the western CONUS
today into Saturday, with low-level flow becoming southwesterly
tomorrow. More seasonable air will advect into the region as a
result, with afternoon temperatures topping out in the upper 80s for
most locations. Depending on how quickly temperatures warm, portions
of central Missouri may reach the 90s. The southwesterly surface
winds support this rapid warm up, and typically favor lower dew
points. If dew points are not impacted via the downsloping effects
of the Ozarks, then heat index values of up to 105 degrees will
occur across portions of Central Missouri. Therefore, there is a low
chance that these locations may need a Heat Advisory already
Saturday afternoon.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
Issued at 246 AM CDT Fri Jul 24 2026

From Sunday through the end of the period, both deterministic
guidance and global ensembles keep upper-level ridging across the
western CONUS, with northwesterly flow persisting over Middle
Mississippi Valley. However, mid-level ridging will build into the
Middle Mississippi, with southwesterly flow advecting anomalously
warm air into the region. While the CWA will have already sampled
some of this heat on Saturday, the true brunt of it will be realized
starting Sunday. Then, guidance consensus is that 850 mb
temperatures will top out around in the low 20 degrees C, with
values around 25 degrees C on Monday. This climatologically favors
surface temperatures in the mid 90s on Sunday and then upper 90s to
around 100 degrees on Monday. NBM dew points in the mid to upper 70s
seems bold with this degree of heat; however, these values are
supported by a majority of ensemble members. This will produce
widespread heat index values of 105-110 degrees, if not higher.

Variability in the placement of the mid-level ridge increases on
Tuesday, though mid-level temperatures generally hold steady. There
is a portion of guidance that also sends at least a weak front
through the area that has the potential to take the edge off the
heat. However, with the low to mid-levels favoring another day of
oppressive heat, an Excessive Heat Watch has been issued for Sunday
through Tuesday.

Ensemble consensus is that 850 mb temperatures gradually cool as the
western ridge stays in place Wednesday through Friday, though the
exact phasing differs among ensemble clusters. These phasing
differences paired with the threat of additional disturbances within
the northwesterly flow aloft lead to uncertainty in how warm
temperatures will remain. A warmer solution favors high Wednesday-
Friday in the mid 90s, while a cooler solution supports highs
through that stretch in the upper 80s to around 90 degrees. The
current forecast does have temperatures gradually cooling, and
splits the difference between the two solutions.

&&

.AVIATION /06Z TAFS THROUGH 12Z SATURDAY/...
Issued at 540 AM CDT Fri Jul 24 2026

Periods of scattered showers with a low chance for thunderstorms
are expected through a majority of the period at all local
terminals. Given the prolonged period of potential impacts, only
the initial round of rain has been put in the TAFs. Lower
ceilings will move into the region and impact KCOU, KJEF, and
KUIN. Weather model guidance is supporting lower ceilings than
what is currently in the TAFs; however, the diurnal timing
doesn`t climatologically favor such flight conditions. While
ceilings are forecast to lift by this evening, there is a low
chance that they do not clear until after sunset, which will
increase the chance that they remain at least in the MVFR range.

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Extreme Heat Watch from Sunday morning through Tuesday evening
     for MOZ018-019-026-027-034>036-041-042-047>052-059>065-
     072>075-084-085-099.
IL...Extreme Heat Watch from Sunday morning through Tuesday evening
     for ILZ058>060-064-065-069-070-074-079-095>102.

&&

$$

SHORT TERM...Elmore
LONG TERM...Elmore
AVIATION...Elmore