039
FXUS63 KLSX 241947
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
247 PM CDT Fri Jul 24 2026

.KEY MESSAGES...

- On and off showers and a few thunderstorms are forecast through
  Saturday morning.

- Heat and humidity returns to parts of central Missouri
  Saturday and then to the remainder of the area Sunday into
  early next week.

&&

.SHORT TERM /THROUGH SATURDAY/...
Issued at 231 PM CDT Fri Jul 24 2026

A midlevel shortwave is currently across southeast Kansas and
moving east/southeast this evening. This shortwave has helped
produce on/off light rain showers much of the day across the
region, and this is expected to continue overnight tonight
through Saturday morning. The low-level jet, albeit weak, does
increase late this evening into the early overnight hours, so
some uptick in the coverage of showers may occur. Elevated
instability also increases, so a few thunderstorms are possible.
The threat for locally heavy rain has lessened as model
guidance has decreased both the strength of the aforementioned
low-level jet and MUCAPE. Without a strong low-level jet or
high MUCAPE, the chances of deep convection have greatly
decreased. Without robust, deep convection, you will not get
high enough rainfall rates to produce flash flooding. Most
locations are only expected to see 0.10-0.25" of rain, though a
few pockets around 1+" are plausible if convection is realized.

After any lingering shower/weak thunderstorm activity moves out by
midday, heat and humidity will begin to build into the region by
Saturday afternoon. The hottest conditions are forecast to be across
parts of central Missouri, where peak heat index values of 100-105F
are expected. A heat advisory begins for Boone, Moniteau, and Cole
counties on Saturday at noon. Farther east, it will be a lot warmer
than today, but highs in the 80s are expected with heat index values
in the 90s.

&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
Issued at 231 PM CDT Fri Jul 24 2026

(Saturday Night - Tuesday)

Heat/humidity is expected to expand eastward across the remainder of
the area on Sunday, with max afternoon heat index readings 105+ for
most locations both Sunday and Monday. There still is not too much
of a signal for a thunderstorm cluster to impact the region during
this time frame in deterministic guidance, though the pattern
does suggest it is possible. The heart of the mid/upper level
anticyclone stays well to our west, and forward-propagating
Corfidi vectors suggest any complex to our north very well may
move south into our region. That appears to be an unlikely
possibility, but something that not only could prevent advisory
criteria HI values on a given day, but would also pose a threat
for damaging winds.

There is a bit better of a signal for some type of cold frontal
passage late Monday night - Tuesday, though the timing varies some
12+ hours amongst model guidance. In addition, there are some
discrepancies on the air mass behind this cold front. Regardless,
it does not look like a significant cool down, but could
provide enough relief from the heat to get back below advisory
criteria. Therefore, elected to have the heat advisory go only
through Monday for now, with the possibility it may need to be
extended in time for portions of the area.


(Tuesday Night - Next Friday)

Even slower model guidance has the cold front through the entire
area by Tuesday night into Wednesday. Again, there are no signs
of a significant cool down behind this front, but enough to
allow the bi-state area to get back closer to normal
temperatures for late July. Mostly dry weather is also expected
to continue, though we will have to keep an eye on at least the
possibility of ridge-running shortwaves as the mid/upper level
anticyclone shifts more toward the desert southwest.

&&

.AVIATION /18Z TAFS THROUGH 00Z SUNDAY/...
Issued at 1226 PM CDT Fri Jul 24 2026

Light rain is ongoing across much of eastern Missouri and far
western Illinois. Visibilities have stayed VFR for the most
part, and believe this will continue. Low MVFR ceilings are
being observed just west of KCOU/KJEF and should move into these
sites within the next 1-2 hours. Stratus is then forecast to
move out of central Missouri this evening, but may impact
northeast Missouri and west-central Illinois (including KUIN)
late this afternoon/evening. The threat for scattered showers
(and possibly a rumble of thunder) continues tonight through
Saturday morning, but confidence is low on where activity will
focus so kept TAFs dry for now.

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Heat Advisory from 11 AM Sunday to 9 PM CDT Monday for MOZ018-
     019-026-027-034>036-042-049>052-059>065-072>075-084-085-
     099.
     Heat Advisory from 1 PM Saturday to 9 PM CDT Monday for MOZ041-
     047-048.
IL...Heat Advisory from 11 AM Sunday to 9 PM CDT Monday for
     ILZ058>060-064-065-069-070-074-079-095>102.

&&

$$

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