Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

820
FXUS63 KLSX 280811
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
311 AM CDT Fri Aug 28 2026

.KEY MESSAGES...

- Summer-like heat returns next week, with afternoon
  temperatures for some locations approaching 100 degrees.

&&

.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 309 AM CDT Fri Aug 28 2026

Water vapor imagery shows the axis of an upper-level trough entering
the Ohio Valley with a highly amplified ridge over the western
CONUS. This has the Middle Mississippi Valley beneath northwesterly
flow aloft and high pressure centered over the Midwest at the
surface. With this pattern holding through the day, one last day of
seasonable temperatures and light east-northeasterly winds is
expected today.

Tomorrow, the western ridge will quickly build into the Midwest,
shunting the surface high eastward and returning southerly low-level
flow the the CWA. As a result, warm air advection will cause
temperatures to bump up across the CWA. Though, this will be offset
somewhat by cloud cover associated with a passing shortwave. The
result will be afternoon temperatures up to 5 degrees above what is
forecast today, particularly across central Missouri where cloud
cover will be less prevalent and warm air advection stronger.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
Issued at 309 AM CDT Fri Aug 28 2026

Our local weather will be driven primarily by two features through
the extended period: upper-level ridging encompassing the eastern
2/3rds of the CONUS, and a surface high centered over the Southeast.
These features will combine to keep flow over the Middle Mississippi
Valley southwesterly through the depth of the atmosphere, which will
provide a continuous feed of abnormally warm air. The heart of the
thermal ridge builds aloft Sunday, characterized by 850 mb
temperatures in the low 20s degrees C, and is fully realized Monday
through Friday. During this stretch, a majority of the CWA will
experience afternoon air temperatures peaking in the mid to upper
90s, with up to a 30% chance per the NBM of highs reaching 100
degrees.

A mitigating factor for dangerous heat levels will be dew points.
Given some degree of southwesterly surface flow through this
stretch, we will have to contend with downsloping from the Ozarks,
which will serve to reduce dewpoints over southeastern Missouri and
into the St. Louis metro area. Additionally, we have passed peak
evapotranspiration season locally, and with a seasonable lack of
widespread recent rainfall, vegetation and soil moisture will do
little to modify dew points. All of this to say, currently
forecasted dew points may be too high, and if that is the case, some
locations will see air temperatures a couple degrees warmer than
forecast. This shift in balance between air temperatures and dew
points will simply lead to similar heat index values to what is
currently forecast. As such, scattered instances of around 100
degrees can be expected. If locations were to need a heat headline,
it would be for duration (heat index of 100+ degrees for four or
more days). Given the current forecast and considering local
climatology, confidence is low at this time that a Heat Advisory
will be needed.

&&

.AVIATION /00Z TAFS THROUGH 06Z SATURDAY/...
Issued at 619 PM CDT Thu Aug 27 2026

Conditions still remain favorable overnight into early Friday
for river valley fog at JEF/SUS/CPS with MVFR visibilities
between 10-14Z. There is also a lower probability (<30%) of IFR
visibilities. Otherwise dry and VFR conditions are expected
through the period with light winds.

&&

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

&&

$$

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