771 
FXUS63 KLSX 030747
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
247 AM CDT Thu Sep 3 2026

.KEY MESSAGES...

- An Extreme Heat Warning is now effect until Saturday evening as 
  the dangerous late season heatwave continues.

- Temperatures are forecast to "cool" slightly Sunday into Labor
  Day before another period of near-record breaking heat returns
  by the middle of next week.

&&

.SHORT TERM /THROUGH SATURDAY/...
Issued at 244 AM CDT Thu Sep 3 2026

The Heat Advisory has been upgraded to an Extreme Heat Warning for 
the entire area with this forecast.  Heat indexes yesterday 
afternoon were at or above 105 degrees over much of the area 
including central Missouri.  These same areas are expected to see at 
or above 105 degrees for four straight days (through Saturday) which 
increases the dangerous nature of this current heatwave.

Persistence will be the best tool through Saturday as the HREF is 
showing an upper ridge building across the central CONUS. 
Temperatures at 850mb are forecast to stay around 22C with deep 
mixing up to 700mb and southwesterly winds keeping highs in the 
middle 90s to near 100 degrees.  Even with the deep mixing, 
dewpoints yesterday afternoon only dropped into the middle 60s to 
around 70 degrees which didn't stop heat indexes from climbing above 
105 degrees in many areas.  The soil temperatures have gone up 
slightly here at the NWS office over the past week which may also 
help boost temperatures, and a weak "cold" front will be moving in 
from the east by late Saturday which may slightly elevate dewpoints. 
Have kept the NBM temperatures and used a short term blend for 
dewpoints to account for the mixing which produces heat indexes 
between 102 and 110 degrees during the afternoon and early evening 
hours.   

There were some brief showers yesterday over central Missouri as the 
atmosphere became uncapped, but they did not last long under the 
upper ridge.  We may see similar activity today and Friday, but the 
area will remain mainly dry with the ridge.  There will be a 
slightly better chance on Saturday as the ridge shifts west and the 
both the ECMWF/GFS hint at a MCS moving southeast across the Midwest 
Friday night into Saturday, though it is farther east than 24 hours 
ago. This eastward trend is also reflected in the LREF at it now 
only has 15-25% of its members producing rain at St. Louis on 
Saturday.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
Issued at 244 AM CDT Thu Sep 3 2026

Model guidance remains in good agreement with a weak cold front 
moving through the area Saturday night. The NBM 25th/75th percentile 
temperature forecast at St. Louis for both Saturday and Sunday is 
still only showing 3-5 degree spread. Most areas will remain dry as 
only 15-20% of the LREF members are producing rain on Saturday night 
and Sunday.  Temperatures will still be unseasonably hot Sunday and 
Monday with highs in the lower to middle 90s.  Dewpoints will be 
slower to drop with the easterly winds and readings mainly in the 
70s on Sunday versus 60s on Monday.  This will result in heat 
indexes on Sunday over parts of the area still climbing over 100 
degrees which may require an extenion to the going headlines. 
Temperatures will climb back into the middle 90s by the middle 
of next week as the upper high builds back into the area. Highs 
will be close to records again over parts of the area. The upper
high will also keep the area dry through the middle of next 
week.

&&

.AVIATION /00Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1045 PM CDT Wed Sep 2 2026

Stationary high pressure and ridging means aviation concerns are
limited to minor wind shifts. I can't rule out a pinhead 
showers tomorrow afternoon, but given the low probability of 
this occurring at all and the extremely small areas that would 
be impacted by these showers if they do occur, they are not 
worth mentioning in the TAFs.

&&

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

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

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

September 5
KSTL: 103/1954...80/1899
KCOU: 103/1899...75/1983
KUIN: 100/1925...76/1912

&&

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

&&

$$

SHORT TERM...Britt
LONG TERM...Britt
AVIATION...BSH
CLIMATE...Britt