Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

975
FXUS63 KLSX 291130
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
630 AM CDT Mon Jun 29 2026

.KEY MESSAGES...

- Dangerously hot and humid conditions continue through the end of
  the week.

- After a dry few days, chances of showers and thunderstorms begin
  to increase late in the week and this weekend.


&&

.SHORT TERM... (Through Tuesday)
Issued at 232 AM CDT Mon Jun 29 2026

Ridging continues to build over the center of the country in
response to a digging trough over the western US and a trough over
the Northeast. With the ridge centered near the Mississippi River,
our region will continue to see some of the worst of the heat
today and Tuesday, with temperatures reaching the mid to upper 90s
in the afternoon. With a very humid air mass in place and a
continued southerly low level flow pumping moisture off the Gulf,
we`ll see oppressive levels of humidity continue as well. The
combination of heat and humidity will cause heat index values to
rise well above 100 degrees today area wide, with some areas near
110. A Heat Advisory continues area wide with an Extreme Heat
Warning for the St Louis metro and areas of southern Illinois.
Areas within the warning are likely to see the most extreme heat
index values due to slightly higher humidity values. The ridge
peaks in intensity over the next 24 to 36 hours or so, likely
leading to some of the hottest temperatures of this heat wave. The
ridge also suppresses all attempts at convection, so we also have
high confidence in a dry forecast.

Kimble

&&

.LONG TERM... (Wednesday through Saturday)
Issued at 232 AM CDT Mon Jun 29 2026

The ridge expands eastward for the middle to later part of this
week. We don`t really get a break from the heat, but it does have
the effect of allowing better chances of showers and thunderstorms
to develop. More organized areas of storms are likely on the
periphery of the ridge from the Central Plains to the Great Lakes
where frequent shortwave impulses rotate around the ridge. This is
expected to stay well to the north of our area, too far away to
provide meaningful heat relief. However, with the ridge
broadening out a bit we`ll see less capping and a better chance of
air mass thunderstorms each afternoon. This doesn`t really stop
the heat as it will still get hot and humid before and after these
storms, but it may provide temporary relief locally. Some
deterministic guidance appears to show subtle embedded troughs
lifting northward within the tropical air mass on the western side
of the ridge, locally enhancing thunderstorm activity. Low
resolution ensemble guidance is showing 24-hr rain chances rising
to 30 to 50 percent by Friday and Saturday.

By this weekend, all guidance is showing some restructuring of the
ridge, with it generally reorganizing to the west across the
Rockies. This opens our area up to better potential for troughing
and even a potential cold frontal passage by Sunday. This would
bring a more solid end to the extreme heat. After coordinating
with neighboring offices, we`ve extended the heat headlines
through Friday when we still have strong confidence in dangerous
heat continuing. While it`s likely the heat lasts into Saturday as
well, there`s still enough uncertainty with the better rain
chances that we don`t quite have the confidence to extend it
through Independence Day just yet.

Kimble

&&

.AVIATION...  (For the 12z TAFs through 12z Tuesday Morning)
Issued at 630 AM CDT Mon Jun 29 2026

A few high clouds are around today, but we`ll stay VFR at all
terminals. Winds are out of the south, gusting to around 20KT
during the heat of the day, diminishing this evening.

Kimble

&&

.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