308 
FXUS63 KLSX 301720
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
1220 PM CDT Sun Aug 30 2026

.KEY MESSAGES...

- Record-threatening and potentially dangerous heat is expected
  through this week.

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 317 AM CDT Sun Aug 30 2026

Upper-level ridging is building into the Midwest per morning water 
vapor imagery as an expansive area of surface high pressure sits over 
the Southeast. As the upper-level ridge continues to build into the 
region today, 850 mb temperatures will warm to around 22 C. Deep 
mixing is expected given mostly clear skies, favoring surface 
temperatures in the mid to upper 90s. Dew points largely in the low 
to mid 60s will lead to little to no heat index, with southwesterly 
winds around 10 mph helping to lessen the feel of the heat. 

With the large-scale pattern holding and temperatures only bottoming 
out in the low to mid 70s early Monday morning, widespread upper 90s 
are expected for highs during the afternoon. The NBM has dew points 
trending upward on Monday by a couple of degrees; however, there are 
a few factors why confidence in dew points increasing is low. First, 
the bias-corrected guidance the NBM is based off of is likely being 
influenced by the typical summer humidity of the last couple of 
months. Next, surface flow will be southwesterly off the Ozark 
Plateau leading to adiabatic warming that will give temperatures a 
slight boost and decrease dew points. Therefore, dew points tomorrow 
have been decreased slightly, with resulting afternoon heat index 
values hovering around 100 degrees.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Issued at 317 AM CDT Sun Aug 30 2026

The axis of the upper-level trough will still be oriented along the 
Mississippi River at the start of the extended period on Tuesday, 
with the surface high holding strong over the Southeast. With this 
pattern holding through at least Thursday, the early week heat will 
only continue. One variable that may fluctuate is dew points, as 
continuous southerly flow with uninhibited Gulf access will gradually 
advect greater moisture into the area. Assuming high daily high 
temperatures top out in the upper 90s to around 100 degrees, this 
would lead to an uptick in heat index values. While this is the 
current NBM solution, an increase in humidity would lead to a couple-
degree decrease in temperatures. Additionally, there is a strong 
consensus among guidance for surface flow to be out of the 
southwest daily, which would lower dew points and boost temperatures 
thanks to downsloping off the Ozarks. Therefore, confidence remains 
low to medium in heat index magnitude as we get later into the week. 

Confidence decreases in our local weather Friday into the weekend, 
as guidance notably diverges on the phasing of the upper-level 
ridge. While there is some consensus on the ridge amplifying, where 
exactly this occurs across the CONUS varies among deterministic 
guidance and ensemble clusters. If the ridge axis remains generally 
over the Midwest, then we will see a continuation of the heat into 
the weekend. If the ridge amplifies over the Plains as some guidance 
suggests, then the CWA will be beneath northwesterly flow and 
temperatures will decrease. The current forecast splits the 
differences with warm by gradually decreasing temperatures through 
the weekend.

&&

.AVIATION /18Z TAFS THROUGH 00Z TUESDAY/...
Issued at 1217 PM CDT Sun Aug 30 2026

VFR conditions are expected to prevail at all sites through the
18Z TAF window. Breezy southwest winds this afternoon will
weaken and shift to due southerly overnight. A few weak showers
and thunderstorms may pass just to the north of UIN this
afternoon and evening, but are not expected to impact the
terminal.

.CLIMATE...
Issued at 305 AM CDT Sat Aug 29 2026

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

August 31 
KSTL: 103/2013...79/2013
KCOU: 103/1913...78/1947
KUIN: 100/2011...76/1924

September 1
KSTL: 104/2011...82/2011
KCOU: 102/1913...76/1913
KUIN: 104/2011...78/2011 

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

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Heat Advisory from noon Monday to 8 PM CDT Friday for MOZ018-
     019-026-027-034>036-041-042-047>052-059-060-062-065-
     072>075-084-085-099.
     Extreme Heat Watch from Monday afternoon through Friday 
     evening for MOZ061-063-064.
IL...Heat Advisory from noon Monday to 8 PM CDT Friday for 
     ILZ058>060-064-065-070-095>099.
     Extreme Heat Watch from Monday afternoon through Friday 
     evening for ILZ069-074-079-100>102.

&&

$$

SHORT TERM...Elmore
LONG TERM...Elmore
AVIATION...BRC
CLIMATE...Elmore