381
FXUS63 KLSX 010748
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
248 AM CDT Tue Sep 1 2026

.KEY MESSAGES...

- Unseasonably hot weather is expected to continue the rest of
  the week.

&&

.SHORT TERM /THROUGH WEDNESDAY/...
Issued at 246 AM CDT Tue Sep 1 2026

The latest water vapor imagery is showing the large upper high that
is bringing the dry and unseasonably hot weather to our area
centered over southern Missouri early this morning.  The HREF is
showing the center of this high shifting slowly east through
tomorrow while the the low level flow remains south-southwestly
across the CWA.  This will keep the area hot and dry with 850mb
temperatures around 22C through tomorrow with high temperatures back
into the mid 90s to around 100 degrees in a few spots.  Looking back
at yesterday`s dewpoints, the NBM still looks to be running high
over most of the area.  I have combined the NBM with other short-
term ensemble guidance that results in values that aligns better
with the late growing season and recent dry weather. This results in
heat index values in the 98-105 degree range both afternoons.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Issued at 246 AM CDT Tue Sep 1 2026

Not much change is expected late this week as the upper high
will retrograde westward across the area and eventually builds
over the Plains over the weekend. The LREF is showing the
surface high remaining anchored over the southeast CONUS which
will keep south to southwesterly flow across the area at the
same time 850mb temperatures remain around 22C keeping highs and
consequently heat indexes nearly the same Thursday and Friday.

There is no plan to extend the going heat advisory at this point,
though it may need to be extended in the future depending on how
quickly the upper high moves off to the west.  The latest NBM and
LREF is in relatively good agreement that highs will climb well into
the 90s again on Saturday with dewpoints in the 60s resulting in
another day with heat indexes climbing above 100 in many locations.
There still is some question in how quickly a weak cold front will
move into the region from the east over the weekend which will
provide some relief from the heat, with the quicker passage bringing
slightly cooler temperatures on Saturday vs. Sunday.  The front will
also bring the potential for moisture pooling which will also
increase dewpoints which could raise dewpoints and consequently heat
indexes most likely on Saturday.  At this point it looks like
Saturday will still be the hotter day compared to Sunday as there is
increasing spread seen in the ensemble output on Saturday vs. Sunday.

Even with a front moving through the area under northwest flow, the
upper high will act to suppress shower and thunderstorm development
with only 25% over the LREF members producing precipitation Saturday
into Labor Day.  While some relief is expected behind the front,
highs are still forecast to be in the 90s early next week.

&&

.AVIATION /00Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1034 PM CDT Mon Aug 31 2026

Confidence is high in dry and VFR flight conditions prevailing
at all local terminals through the forecast period.

&&

.CLIMATE...
Issued at 1118 AM CDT Mon Aug 31 2026

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

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

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 Friday for MOZ018-019-026-027-
     034>036-041-042-047>052-059>065-072>075-084-085-099.
IL...Heat Advisory until 8 PM CDT Friday for ILZ058>060-064-065-069-
     070-074-079-095>102.

&&

$$

SHORT TERM...Britt
LONG TERM...Britt
AVIATION...Elmore
CLIMATE...Britt