017
FXUS63 KLSX 271941
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
241 PM CDT Mon Jul 27 2026

.KEY MESSAGES...

- One last day with dangerous heat and humidity is forecast on
  Tuesday along/south of I-70.

- A few strong to severe storms are possible with damaging through
  late this evening in parts of south-central Illinois.

- Widespread heat relief is expected by Wednesday, with near
  normal temperatures through the end of the work week.

&&

.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 239 PM CDT Mon Jul 27 2026

Dangerous heat and humidity remains the main story today with
temperatures climbing well into the mid 90s as of 2 PM. A few
spots today may touch the century mark. Dewpoints are still
unseasonably high as well (~90th percentile), though are an
improvement compared to yesterday. Heat index values are mostly
in the 105-110F range, and may come up another couple of degrees
later this afternoon.

Chances of showers and thunderstorms is the next concern through
this evening. Ongoing severe convection near and just southeast of
Chicago should continue to move south/southeast and stay away from
our region. There have been some subtle signs at development farther
west into western Illinois over the past 1-2 hours. GOES-19 also is
showing a westward-propagating gravity wave, which could also impact
convective initiation over the next 1-2 hours. IF storms can develop
and strengthen, they may clip our south-central Illinois counties
this evening. Damaging winds would be the main threat if any storms
move into our region. Finally, there is some weaker elevated
convection as far west as the Missouri River near the NE/IA border.
These storms have been on/off nearly all day and have never been
able to move much southeast due to strong capping. The expectation
is for this cap to continue to help shield central/northeast
Missouri from these storms making it into the area.

The synoptic cold front is expected to move southward slowly
overnight tonight through Tuesday morning. This boundary may help
serve the focus for a few isolated (weaker) thunderstorms with as a
weak low-level jet strengthens overnight. A better chance (30%) of
showers and a few storms comes late morning through the evening
hours on Tuesday as a midlevel shortwave trough ejects out of the
mid-Missouri Valley. This activity looks to be behind the synoptic
cold front and elevated in nature. Strong to severe storms are
therefore not likely as the threat for damaging winds with elevated
convection is quite low and chances of severe hail making it to the
surface also very low.

Dangerous heat/humidity remains a top concern on Tuesday, though the
threat area will shift more to the south and out of areas north of I-
70. Lingering high dewpoints though north of the cold front will
still make it feel like 100-105+ for those along/south of I-70.
Where 105+ values are expected once again, continued the heat
warning another day with an advisory to the north for locations
where peak heat index values of 100-105F are forecast.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Issued at 239 PM CDT Mon Jul 27 2026

Dry weather with near normal temperatures is forecast Wednesday
through Thursday thanks in part due to a weak ridge of surface high
pressure across the area. We are still looking for a good chance (50-
70%) of showers and thunderstorms from a potential MCS Thursday
night - Friday night. Ensemble guidance has shifted a bit more
toward a slower midlevel trough passage this weekend, with a
minority (23%) of members from the LREF showing a cutoff midlevel
low. This means a couple of things, but namely: 1) cooler daytime
temperatures Friday through next weekend and 2) lingering rain
chances.

&&

.AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 1220 PM CDT Mon Jul 27 2026

While a stray storm or two cannot be ruled out, the expectation
is for the terminals to say dry through the period. Southwest
winds are expected to veer behind a cold front to the
north from north to south late tonight into Tuesday morning.

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Extreme Heat Warning until 9 PM CDT this evening for MOZ018-
     019-026-027-034>036-041-042-047>052-059>064.
     Heat Advisory from 9 PM this evening to 7 PM CDT Tuesday for
     MOZ041-047>052-059>064.
     Extreme Heat Warning until 7 PM CDT Tuesday for MOZ065-072>075-
     084-085-099.
IL...Extreme Heat Warning until 9 PM CDT this evening for
     ILZ058>060-064-065-069-070-095>100.
     Heat Advisory from 9 PM this evening to 7 PM CDT Tuesday for
     ILZ064-069-070-100.
     Extreme Heat Warning until 7 PM CDT Tuesday for ILZ074-079-101-
     102.

&&

$$

SHORT TERM...Gosselin
LONG TERM...Gosselin
AVIATION...Gosselin