Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

491
FXUS63 KLSX 280229
AFDLSX

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

.KEY MESSAGES...

- Seasonable temperatures are expected through Saturday with
  summerlike heat returning Sunday and through next week.

&&

.SHORT TERM /THROUGH SATURDAY/...
Issued at 212 PM CDT Thu Aug 27 2026

Current upper air analysis shows a building ridge over the west-
central CONUS and a center of low pressure over Hudson Bay. With
this regime, northwesterly flow is present across the northern
Great Plains and Midwest, which is bringing a cooler and,
according to mid-level water vapor imagery, drier air mass to
the region. As a result, were seeing more seasonable
temperatures across the region with high temperatures this
afternoon in the low to mid 80s and dewpoints in the low 60s.
Fridays temperature will be similar today, but will be a couple
of degrees higher than today due neutral low-level temperature
advection. Low temperatures overnight for both tonight and
Friday night will be in the low 60s. By Saturday, model guidance
has the ridge to our west starting to push east. As a result the
high temperatures on Saturday will increase into the mid to
upper 80s. River valley fog tomorrow morning before sunrise is
expected due to the interaction between the calm winds, cooler
air temperatures, and warmer water, but it should clear out
shortly after sunrise.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Issued at 212 PM CDT Thu Aug 27 2026

The weekend and into next week are looking to remain dry, as
upper level subsidence sets in as the ridge moves east over into
the central CONUS. The exception is Sunday and Monday, where
northeastern MO and west-central IL could see some rainfall.
Model guidance indicates strong warm air advection on the nose
of the low level jet over IA and western Great Lakes will
provide support for multiple rounds of convection in that area.
Convective remnants on the southern edge of these systems could
dip south into northeastern MO and west-central IL, though
confidence in this happening is low. Currently, LREF
probabilities of even measurable precipitation are 20-40%, while
the probabilities for even somewhat meaningful rainfall (>0.25)
are even lower at less than 10%.

As the ridge sets in, higher temperatures are expected to be
well above average beginning Sunday. Cluster analysis shows that
the 500 mb heights associated with the ridge are anomalously
high, being above the 95th percentile compared to climatology.
Current ensemble guidance is in agreement that once this
unseasonal ridge sets in over the central CONUS, it will remain
over the region keeping the above average temperatures around
for most, if not all, of the week. The 850 mb temperatures will
be at least in the low to mid 20s C (above 95th climatological
percentile), translating to surface temperatures in the mid to
upper 90s, There is a chance (30-50%) that central and east-
central MO may reach 100 F or higher, which could be caused by
southwesterly downsloping flow off the Ozark Plateau. While the
temperatures are expected to be above average and perhaps the
warmest weve seen all year, the dewpoints are anticipated to be
notably lower compared to previous heatwaves. Model guidance
indicates dewpoints in the low to mid 60s, with a small chance
(20-40%) of dewpoints 70 F or greater in northeastern MO and
west-central IL on Tuesday and Wednesday. As a result, heat
index values in the upper 90s are possible with some areas
peaking to near 100 F by mid week. This means that despite
potentially warmer temperatures than earlier in the year, this
heatwave is not expected to be as extreme as those from earlier
in the summer.

&&

.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...Asel/BSH
LONG TERM...Asel/BSH
AVIATION...Britt