751
FXUS63 KLSX 231126
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
626 AM CDT Wed Sep 23 2026

.KEY MESSAGES...

- Seasonably cool temperatures are expected to continue through
  the end of the week.

- Rain chances return to the area this weekend into next week.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 336 AM CDT Wed Sep 23 2026

An anomalously strong 1038mb surface high (>99th climatological
percentile) is located over eastern Canada, which is supporting
north-northeasterly flow across our region. This north-
northeasterly flow is promoting low-level cold air advection,
which in combination with a mid/upper-level shortwave over the
Midwest is supporting the development of widespread low stratus
over eastern and southeastern IL. The clouds that were over our
area yesterday are moving to the west and dissipating allowing
for a clearing in the clouds over southwestern IL and
southeastern MO. This should allow temperatures to drop slightly
more in those areas, possibly dropping into the mid to upper 50s
briefly. The low stratus moving west from IL will move over our
area today before stalling just west of the Mississippi River.
This will moderate our high temperatures similar to yesterday,
but thanks to the clearing some areas will be starting with
lower temperatures this morning. According to conditional
climatology for diurnal temperature swings, with the clouds we
are expected to experience today, high temperatures may only
rebound around 7 degrees along and east of the Mississippi
River. This could result in lower high temperatures than
yesterday (upper 60s and low 70s). Current NBM guidance
continues the cloud cover into Thursday, but has been currently
indicating that high temperatures Thursday will be about 5-10
degrees warmer than today. The NBM has been struggling to handle
temperatures when widespread cloud cover is expected, so I
wouldnt be surprised if high temperatures would turn out
similar to today.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Issued at 336 AM CDT Wed Sep 23 2026

The rest of the work week looks to continue to be similar to
today and tomorrow, but with slightly less cloud cover and a
gradual warming into the weekend. The GFS and EPS ensembles are
showing that a mid/upper-level ridge is expected to build over
the Midwest by the weekend. This would bring southerly flow back
to the area, possibly increasing temperatures early next week.
There remains uncertainty in the exact magnitude of the warm up
however. NBM and LREF interquartile ranges for Saturday through
Tuesday are around 7-8 degrees, so guidance is unsure if we will
remain in the mid to upper 70s or heat up into the mid 80s.
These wide ranges are driven by a return of rain chances which
could cool temperatures as low as the mid 60s (10% percentile).
The NBM does hint at a possible return to the 90s with the 75th
percentile for Tuesdays high temperature being in the upper 80s
to low 90s. Long-range deterministic models are also hinting of
a deep trough moving through the central Great Plains on Tuesday
that could bring a cold front to the area Tuesday into
Wednesday, but ensembles during the same time are having a
difficult time capturing the timing of the front with
interquartile ranges around 10 degrees by the middle of next
week; temperatures could remain in the 80s or drop back into the
70s.

With the approaching warm up, our chances of rain increase
again. The LREF is showing a 40-70% chance of some rainfall
across central and northeastern MO over the weekend. Guidance
during the last several days has been pushing these rain chances
farther east into our area with each model run. The possible
cold front during the middle of the week also brings the
greatest chance of widespread rain through the forecast period.
LREF guidance shows a 70-80% chance of rain across our entire
area.

&&

.AVIATION /12Z TAFS THROUGH 18Z THURSDAY/...
Issued at 625 AM CDT Wed Sep 23 2026

Widespread low stratus is moving west through southern IL and
will cause MVFR ceilings to impact the St. Louis metro and UIN
terminals during the morning hours, but should raise to VFR by
the afternoon. These low clouds are expected to stall just west
of the Mississippi River, so the central MO terminals will
continue to experience VFR conditions. More clouds are expected
to be in the area tomorrow and could bring another round of MVFR
ceilings in the morning, but there is some uncertainty if the
ceilings will get that low. As a result, a SCT025 was included
in STLs TAF for tomorrow morning to highlight the possibility
of these lowered ceilings.

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.

&&

$$

SHORT TERM...Asel/Gosselin
LONG TERM...Asel/Gosselin
AVIATION...Asel/Gosselin