Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

047
FXUS63 KLSX 282329
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
629 PM CDT Fri Aug 28 2026

.KEY MESSAGES...

- Seasonal temperatures continue for today and tomorrow, then
  summerlike heat returns next week with temperatures
  approaching 100 F.

&&

.SHORT TERM /THROUGH SUNDAY/...
Issued at 205 PM CDT Fri Aug 28 2026

Current upper air analysis shows a building ridge over the west-
central CONUS and a center of low pressure over east-central
Canada creating northwesterly flow aloft and a high pressure
center over the western Great Lakes at the surface. This pattern
has allowed for seasonal temperatures to continue this afternoon
and overnight, and lower than average dewpoints (below 25th
climatological percentile). Saturday, model guidance has the
ridge to our west starting to push east, resulting in the high
temperatures increasing into the upper 80s to low 90s. As the
ridge sets in, temperatures are expected to be 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. This translates to
another increase in temperatures during the day on Sunday with
highs in the low to mid 90s.

On Sunday, northeastern MO and west-central IL have the
potential for some rainfall. Model guidance indicates strong
warm air advection on the nose of the low level jet over IA and
western Great Lakes that 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 10-40%, while the probabilities for even
somewhat meaningful rainfall (>0.25) are virtually zero.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Issued at 205 PM CDT Fri Aug 28 2026

Next week is looking to remain dry, with upper level subsidence
setting in as the ridge moves east over the central CONUS.
Current ensemble guidance is in agreement that once this
anomalous ridge sets in over the central CONUS, it will remain
over the region keeping the above-average temperatures around
through at least Friday. 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. LREF guidance shows there is a chance (30-60%) that
central and east-central MO could 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, perhaps the warmest we`ve seen all year, the dewpoints
are anticipated to be notably lower compared to previous
heatwaves. Long range 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. 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. There still remains uncertainty of the magnitude
of the moisture, and how much it will affect the resulting heat
index values. Given that, our confidence is low to issue a heat
headline for this event.

&&

.AVIATION /00Z TAFS THROUGH 06Z SUNDAY/...
Issued at 629 PM CDT Fri Aug 28 2026

The only concern this TAF period will be the potential for fog
development in river valleys early Saturday morning, impacting KSUS,
KCPS, and KJEF with bouts of MVFR to IFR visibilities. Otherwise,
dry and VFR flight conditions will prevail with winds becoming
southerly/southeasterly on Thursday as a surface high pressure
center departs.

&&

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

&&

$$

SHORT TERM...Asel/MRB
LONG TERM...Asel/MRB
AVIATION...Pfahler