Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

525
FXUS63 KLSX 271721
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
1221 PM CDT Thu Aug 27 2026

.KEY MESSAGES...

- Near to slightly below normal temperatures are expected
  through Friday night before summerlike heat returns Sunday
  into next week.

&&

.SHORT TERM /THROUGH FRIDAY NIGHT/...
Issued at 247 AM CDT Thu Aug 27 2026

The surface cold front has just cleared far southeast Missouri,
with winds turning light out of the north/northwest and
dewpoints beginning to lower into the 60s. A surface ridge of
high pressure is expected to slowly migrate eastward from the
mid-Missouri Valley to the Great Lakes over the next 36-48
hours. Cooler and drier air will infiltrate the area as a
result, with near to slightly below normal temperatures favored
through Friday night. A mostly clear sky is also expected, with
the exception of scattered to broken cumulus/stratocumulus today
along/east of the Mississippi River. These clouds along with
moderately strong low-level cold air advection is expected to
yield highs this afternoon mostly in the low to mid 80s.
Temperatures should top out a degree or two warmer on Friday due
to more plentiful sunshine and neutral low-level temperature
advection. Lows each night are expected to be in the upper 50s
to low 60s, given favorable conditions for radiational cooling
associated with the surface ridge. Some spotty mid 50s are even
possible, particularly Friday night in favored river valleys
across east central and southeast Missouri. Steam fog will also
likely occur over river valleys due to air-water temperature
differences of 20+ degrees.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Issued at 247 AM CDT Thu Aug 27 2026

Moderating temperatures are expected on Saturday as the surface
ridge pushes off to the east toward the eastern seaboard. Highs are
forecast to climb back into the upper 80s to near the 90 degree
mark, or slightly warmer than normal for the date.

Ensemble guidance remains in very good agreement with the synoptic
pattern across the CONUS late this weekend into next week. Anomalous
mid/upper level ridging will build into the area on Sunday, with 500-
hPa heights above the 95th percentile. This west-east oriented
midlevel ridge very likely will continue through next Thursday, and
potentially beyond. Clusters of the 500-hPa height pattern show 3 of
the 4 clusters (~89% of LREF membership) with this pattern through
Thursday, so there is pretty high confidence that once the
summertime heat sets back in Sunday, it will have legs. Mean
temperatures at 850 hPa climb well above +20C, and are expected to
exceed the 95th percentile of climatology. Dewpoint (relative
humidity) levels are likely to start off much lower than earlier
this summer. While not a "dry" heat by any means, it does look like
dewpoints will stay predominantly in the 60s. Probabilities on the
LREF never climb above 40% at any time for 70+ dewpoints, though do
get close in northeast Missouri and west-central Illinois. This is
where there is a bit more uncertainty with temperatures as there
remains a signal for a frontal boundary to stall, likely just to the
north. This boundary may serve as the focus for showers and
thunderstorms on the northern periphery of the mid/upper level
ridge. However, for most of the area, there is very high confidence
in well-above normal temperatures the entire period. High
temperatures well into the 90s are forecast each day, and it is
conceivable that there could be a day (or two) where mixing is deep
enough with favorable downslope flow off of the Ozark Plateau to
yield highs nearing the century mark in central/east central
Missouri, including metropolitan St. Louis. Heat index values should
tend to climb into midweek, with peak values near or slightly above
100 degrees expected in some locations.

&&

.AVIATION /18Z TAFS THROUGH 00Z SATURDAY/...
Issued at 1211 PM CDT Thu Aug 27 2026

Mostly VFR conditions are expected to prevail for the TAF
period. Fog is expected in the early morning hours before
sunrise in the river valleys affecting KJEF, KSUS, and KCPS, but
should clear quickly after sunrise. There is a slight chance
for fog near KUIN during the same time, but confidence is low it
will be impactful so it was left out of the TAF.

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.

&&

$$

SHORT TERM...Gosselin
LONG TERM...Gosselin
AVIATION...Asel/BSH