732 
FXUS63 KLSX 021722
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
1222 PM CDT Wed Sep 2 2026

.KEY MESSAGES...

- The dangerous heat is expected to continue through Saturday.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 221 AM CDT Wed Sep 2 2026

I have made no changes to the going heat advisory and kept it in 
effect through Saturday evening with this forecast. The latest 
surface analysis continues to show a surface high centered over the 
eastern CONUS with a surface front well north of the CWA over Iowa 
and Wisconsin. Temperatures have dropped back into the 70s in much 
of the rural parts of the CWA while they remain in the 80s in the 
heat island of St. Louis.  The large upper high which is responsible 
for the late season hot and dry weather was centered over Kentucky 
and Tennessee this morning.  The HREF is showing a ridge building 
back over the central CONUS in response to an upper trough digging 
into the West Coast.  The 850mb temperatures will stay in the 20-23C 
range (>90th percentile) through tomorrow with RAP soundings showing 
mixing up to 700mb supporting highs in the mid 90s to near 100 
degrees with a slight drop in dewpoints during the afternoon. This
results in heat index values in the 98-106 degree range both 
afternoons.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Issued at 221 AM CDT Wed Sep 2 2026

The LREF continues to show the upper ridge building over the central 
CONUS with the upper flow becoming northwesterly over Missouri and 
Illinois by the weekend.  The models have been consistent keeping 
850mb temperatures around 22C through Saturday before a weak cold 
front moves east across the area Saturday night.  The NBM 25th/75th 
percentile forecast at St. Louis for both Saturday and Sunday is now 
only showing a 4-5 degree spread.  This supports keeping the 
advisory going through Saturday before both temperatures and 
dewpoints fall slightly on Sunday which will push the heat index 
below advisory criteria.  Even with this said, there does remain 
some uncertainty this far out as both the GFS/ECMWF are hinting at a 
MCS moving southeast over the area on Saturday.  This is supported 
by 20-35% of the LREF members producing rain at St. Louis over the 
weekend. However, any "cooling" effects of the rain could be 
countered by moisture pooling by the incoming front which would 
boost dewpoints. As we go into early next week, less than 20% of the 
LREF members have any rain chances as the upper ridge begins to 
build back into the Midwest. Highs are forecast to stay in the 90s, 
though forecast slightly lower dewpoints should keep heat indexes 
below 100 degrees.

&&

.AVIATION /18Z TAFS THROUGH 00Z FRIDAY/...
Issued at 1220 PM CDT Wed Sep 2 2026

Dry/VFR conditions are forecast with west/southwest winds 
backing this evening to the south and then veering to the 
west/southwest Thursday morning.

&&

.CLIMATE...
Issued at 1220 PM CDT Wed Sep 02 2026

Record Highs...Record High Lows (value/year):          

September 2 
KSTL: 101/2011...80/2011 
KCOU: 100/1913...77/1913 
KUIN: 103/1913...80/1913

September 3 
KSTL: 101/2011...80/1913 
KCOU: 103/1939...75/1939 
KUIN: 103/1913...78/1913

September 4 
KSTL: 104/1954...81/1925 
KCOU: 103/1913...73/1947 
KUIN: 105/1913...75/1947

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Heat Advisory until 8 PM CDT Saturday for MOZ018-019-026-027-
     034>036-041-042-047>052-059>065-072>075-084-085-099.
     Air Quality Alert until 8 PM CDT this evening for MOZ061>065.
IL...Heat Advisory until 8 PM CDT Saturday for ILZ058>060-064-065-
     069-070-074-079-095>102.
     Air Quality Alert until 8 PM CDT this evening for ILZ100>102.

&&

$$

SHORT TERM...Britt
LONG TERM...Britt
AVIATION...Gosselin
CLIMATE...Gosselin