199
FXUS63 KLSX 221137
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
637 AM CDT Tue Sep 22 2026

.KEY MESSAGES...

- Seasonably cool temperatures expected to continue through the
  week.

&&

.SHORT TERM /THROUGH WEDNESDAY/...
Issued at 328 AM CDT Tue Sep 22 2026

An anomalously strong 1030mb surface high is located over
southeast Canada, which is supporting northeasterly flow across
our region. This northeasterly flow is promoting low-level cold
air advection that is supporting widespread low stratus over our
entire area, which is currently visible on GOES-19 satellite
imagery. These clouds moderated our temperatures yesterday and
are expected to continue to impact our temperatures through
tomorrow. Thanks to the clouds, our temperatures didnt cool
very much overnight, dropping only to the low to mid 60s after
having highs in the low to mid 70s. According to conditional
climatology for diurnal temperature swings, with the cloud we
are expected to experience today, high temperatures may only
rebound around 7 degrees to the upper 60s and low 70s, possibly
with mid 70s in southeastern MO. This will likely make today the
coolest day of the week across much of the area.

The surface high is expected to move to the southeast allowing
surface winds to shift to a more northerly wind direction. This
will bring drier conditions to the area to help clear the cloud
cover that we are experiencing. Current NBM and CONSShort
guidance shows clouds are expected to clear in central and
north-central MO, which will allow temperatures to fall into the
upper 50s in that region by Wednesday morning, while eastern MO
and southwest IL will continue to experience cloud cover
preventing low temperatures to drop below 60 degrees. High
temperatures on Wednesday are expected to be similar to today,
but with less cloud in central and north-central MO, highs are
expected to be warmer in the low 70s.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Issued at 328 AM CDT Tue Sep 22 2026

Thanks to the clearing cloud cover, low temperatures Wednesday
night are expected to drop further compared to tonight. Current
guidance shows temperatures dropping into the 50s across the
entire region. As the clouds continue to clear, a gradual
warming trend is expected through the rest of the work week. The
LREF is showing interquartile ranges of only 3-5 degrees each
day for high temperatures, indicating high confidence in these
values.

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 bringing
temperatures back up. There remains uncertainty in the exact
magnitude of the warm up however. LREF interquartile ranges for
Saturday through Monday are 8-10 degrees, so guidance is unsure
if we will remain in the mid to upper 70s or heat up into the
mid 80s. To illustrate next weekend, the 25th percentile of
guidance is in the low to mid 70s and the 75th percentile being
in the mid to upper 80s.

&&

.AVIATION /12Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 636 AM CDT Tue Sep 22 2026

MVFR ceilings are expected to prevail through the morning and
into the afternoon, except for at COU where IFR ceilings are
present before lifting to MVFR later this morning. During the
morning there are fuel alternate ceilings expected for the St.
Louis metro terminals. Northerly flow in the afternoon and
evening should bring drier air to the region that will lift
ceilings to allow for VFR conditions around sunset.

&&

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

&&

$$

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