Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

253
FXUS63 KLSX 021013
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
513 AM 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 /06Z TAFS THROUGH 12Z THURSDAY/...
Issued at 512 AM CDT Wed Sep 2 2026

Dry and VFR conditions are expected through the period. Light
winds are expected to turn out of the southwest by mid morning
around 10 knots before becoming light again this evening.

&&

.CLIMATE...
Issued at 1118 AM CDT Mon Aug 31 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 from 9 AM this morning to 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 from 9 AM this morning to 8 PM CDT this
     evening for ILZ100>102.

&&

$$

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