Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

995
FXUS63 KLSX 221852
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
152 PM CDT Tue Sep 22 2026

.KEY MESSAGES...

- Hazardous weather is not anticipated through the forecast
  period as temperatures slowly warm.

&&

.SHORT TERM /THROUGH WEDNESDAY NIGHT/...
Issued at 150 PM CDT Tue Sep 22 2026

Current water vapor imagery shows a messy upper-level pattern over
the CONUS, with split flow across the US-Canadian border. This has
low-amplitude troughing stretching from the Northern Plains eastward
into the Northeast. A shortwave rounding the base of the trough is
moving through the Midwest currently, and is responsible for our
current cloud cover. Thanks to this cloud cover and the decreasing
sun angle, our diurnal temperature curve has been muted, with
temperatures this afternoon only expecting to top out around 70
degrees. This effect will carry into tonight, though a surface high
digging further into the Middle Mississippi Valley will help push
temperatures lower tonight than last night - low to mid 50s for most
locations.

Tomorrow, the shortwave will dig southeastward into the Southeast as
upper-level ridging builds into the Plains. As a result, we`ll see
some thinning of the cloud cover that will allow for a little more
surface heating. However, low-level flow will remain northeasterly,
helping keep temperatures similar to today`s for much of the
area.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Issued at 150 PM CDT Tue Sep 22 2026

Both ensemble clusters and deterministic guidance show the axis of
an upper-level ridge centered over the Great Plains. Through Friday,
this ridge will gradually shift eastward, but how amplified it
remains as it does so is uncertain as a shortwave moves into the
Central Plains and Upper Midwest. While the NBM shows surface
temperatures warming in response to the ridge, a majority of
guidance has 850mb temperatures holding steady compared to Thursday,
with southerly flow east-northeasterly. Climatologically, this
doesn`t favor warming temperatures, so I wouldn`t be surprised to
see future NBM runs come in a little cooler. After the effects of
the shortwave depart the region on Saturday, ensemble consensus
shows 850 mb temperatures gradually creeping warmer, favoring a
similar effect at the surface. How warm remains uncertain, as the
NBM is being driven by bias-corrected guidance, which is some cases
is nearly 10 degrees warmer than its unbiased counterparts. This
bias-corrected guidance is training on our recent warmth, so I
suspect that it and the resulting NBM are being too aggressive with
warming early next week. Going strictly off the 25th and 75th
percentile of ensemble guidance, the warmest of guidance would give
us temperatures around 5 degrees above normal, while cooler guidance
would be right around climatology.

As for rain chances, confidence is high that a majority of the area
will not experience a soaking rainfall through the weekend. The late-
week shortwave will be pivoting northeastward and taking the
greatest lift with it. Its trailing cold front will also struggle to
make eastward progression into the CWA, limiting rain chances (up to
50%) to portions of central and northeastern Missouri. This will
serve as the main focus for rain potential through the forecast
period.

&&

.AVIATION /18Z TAFS THROUGH 00Z THURSDAY/...
Issued at 1227 PM CDT Tue Sep 22 2026

Impacts are expected at least through early this evening at the
local TAF sites. A slow moving weather system is currently
passing through the Midwest, providing ample low-level moisture
that has yielded widespread stratus. This stratus has mostly
been in MVFR range, though intermittent pockets of IFR are
expected at KUIN over the next couple of hours thanks to greater
moisture there. Drier air in the low levels will move into the
region this evening and tonight, allowing for conditions to
improve. When this happens exactly is uncertain, and could be
later than what is currently indicated in the TAFs.
Additionally, another round of low MVFR stratus is expected
mainly over Illinois tonight into tomorrow morning. This stratus
may push westward enough to impact KSUS, KSTL, and KCPS.

&&

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

&&

$$

SHORT TERM...Elmore
LONG TERM...Elmore
AVIATION...Elmore