Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

834
FXUS63 KLSX 291942
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
242 PM CDT Mon Jun 29 2026

.KEY MESSAGES...

- An Extreme Heat Warning and Heat Advisory remain in effect
  through Friday for daily dangerous heat index values of 100-105
  degrees.

- While confidence in specifics is low, the Fourth of July
  weekend will be warm and muggy, with a daily threat of isolated
  to scattered showers and thunderstorms.


&&

.SHORT TERM...  (Through Late Tuesday Night)
Issued at 230 PM CDT Mon Jun 29 2026

A highly amplified upper-level ridge can bee seen in current water
vapor imagery centered over the Midwest, with an expansive surface
high impacting much of the east-southeastern portion of the CONUS.
Both features are keeping our skies mostly clear and south-
southwesterly flow deep, leading to another hot and muggy day across
the CWA. With temperatures topping out in the mid 90s this afternoon
and dew points in the mid to upper 70s, heat index values will once
again reach 100-105 degrees. Thanks to the ridge only amplifying and
expanding further into Tuesday, the forecast will be nearly
identical to today`s. With these confidence high in these
conditions continuing through the workweek, the current Excessive
Heat Warning and Heat Advisory will remain in effect and are
unchanged.

Elmore

&&

.LONG TERM...  (Wednesday through Next Monday)
Issued at 230 PM CDT Mon Jun 29 2026

Guidance consensus is that the upper-level ridge will dictate our
local weather through the extend period, but once we reach the
holiday weekend, confidence decreases in specifics. The ridge
remains in place across the eastern CONUS through Thursday, with 850
mb temperatures continuing to gradually decrease. These cooler
low to mid-level temperatures will increase the chance for air
mass convection across the region. While Thursday`s forecast is
dry for much of the area, we will have to monitor a very subtle
disturbance swirling beneath the center of the ridge across the
Ohio Valley. If it is able to drift eastward enough, portions of
southern Illinois may see greater rain chances than currently
forecast.

The ridge deamplifies and broadens Friday into the weekend, which
will open the CWA to additional convection as well as further cool
850 mb temperatures. Run-to-run consistency and guidance spread is
enough that confidence remains low on convective forcing mechanisms
and the degree of any potential cooling, with the 75th percentile of
ensemble guidance favoring highs in the mid 90s, with the 25th
percentile around 90 degrees. If the warmer scenario comes to
fruition, heat headlines would need to be continued beyond Friday
for at least portions of the CWA, while the cooler scenario would
lead to a break from the extreme heat for a majority of the area.
While the current forecast/NBM leans more toward the warmer
solution, fluctuations are expect in the coming days as guidance
hones in on a common solution.

Elmore

&&

.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1257 PM CDT Mon Jun 29 2026

VFR flight conditions and dry weather will prevail at all of the
local terminals through the TAF period.

Elmore

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Heat Advisory until 10 PM CDT Friday for Audrain MO-Boone MO-
     Callaway MO-Cole MO-Crawford MO-Gasconade MO-Iron MO-Knox
     MO-Lewis MO-Lincoln MO-Madison MO-Marion MO-Moniteau MO-
     Monroe MO-Montgomery MO-Osage MO-Pike MO-Ralls MO-Reynolds
     MO-Saint Francois MO-Shelby MO-Washington MO.

     Extreme Heat Warning until 10 PM CDT Friday for Franklin MO-
     Jefferson MO-Saint Charles MO-Saint Louis City MO-Saint
     Louis MO-Sainte Genevieve MO-Warren MO.

IL...Heat Advisory until 10 PM CDT Friday for Adams IL-Bond IL-Brown
     IL-Calhoun IL-Fayette IL-Greene IL-Jersey IL-Macoupin IL-
     Marion IL-Montgomery IL-Pike IL.

     Extreme Heat Warning until 10 PM CDT Friday for Clinton IL-
     Madison IL-Monroe IL-Randolph IL-Saint Clair IL-Washington
     IL.

&&

$$

WFO LSX