Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

593
FXUS63 KLSX 281123
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
623 AM CDT Sun Jun 28 2026

.KEY MESSAGES...

- Dangerous summer heat and humidity begins today with heat index
  values over 100 degrees expected each day through at least
  Thursday. Some areas see heat index values as high as 110
  degrees at times.

- Hot and humid conditions continue into the holiday weekend with
  chances for afternoon showers and thunderstorms returning.


&&

.SHORT TERM...  (Through Late Monday Afternoon)
Issued at 225 AM CDT Sun Jun 28 2026

The pesky frontal boundary that has been nearly stationary across
our region for the last several days is finally starting to push
northward this morning. As it does so, one final band of showers and
embedded thunderstorms is expected to lift northeastward with the
front this morning. Although heavy downpours are possible, storm
motions should be quick enough to prevent a significant threat for
flash flooding.

Behind the front, a very humid air mass will be in place. With
ridging building overhead today, we`ll see afternoon high
temperatures rise some 10 degrees over yesterday`s values, into the
low mid 90s. This added heat combined with the continued humidity
will push heat index values above 100 degrees area wide this
afternoon. There remains some uncertainty on dewpoints today, with
NBM on the higher side of guidance especially across parts of
Illinois. However, looking upstream over the Mississippi delta,
there have been several observations in the last few hours of
dewpoints near 80 degrees. With a southerly flow expected, these
higher dewpoints creeping into southeast Missouri and southern
Illinois makes some sense. Combine this with soggy soils and
elevated water levels on area rivers and this gives us confidence in
some of the highest humidity levels observed across this region
today and tomorrow. As a result, we`ve expanded the Extreme Heat
Warning to include areas near the Mississippi and Kaskaskia Rivers
where heat index values may approach 110 degrees at times. Further
west, a flow off the Ozarks likely leads to a bit lower dewpoints,
though still in the 70 to 75 degree range, where heat index values
of 100 to 105 are more likely.

Kimble

&&

.LONG TERM...  (Monday Night through Saturday)
Issued at 225 AM CDT Sun Jun 28 2026

A large ridge of high pressure is developing aloft, with its center
expected to be near the Mississippi River early this week. It
reaches peak intensity Monday into Tuesday when we are likely to see
our hottest temperatures, in the mid to upper 90s. With continued
high humidity, heat index values are expected to again be over 100
degrees each day, potentially as high as 110 degrees depending on
humidity trends. Despite the warm and humid air mass, capping aloft
prevents daily convection leaving us baking in this air mass.

Later this week, we expect at least subtle adjustments in the
ridge`s intensity and position in response to waves rotating around
it. Eventually the ridge center nudges eastward, allowing slightly
cooler temperatures aloft and less capping. Thus high temperatures
may nudge down a degree or two with better chances of pop up showers
and thunderstorms each afternoon. These will likely be small and
brief in nature with virtually no shear available for storm
organization, but some local heat relief becomes increasingly
possible toward the end of the week. Our greatest confidence in
extreme heat continues to be through Thursday, though it will be
continued hot and humid through the Independence Day weekend as
well. Later expansions of the heat headlines are likely as
confidence in the precise heat index forecast improves. At least
advisory level heat looks likely through at least Saturday, July 4.
Beyond that more guidance sources show the potential for a cold
front to drop into the region accompanied by some degree of
troughing, thus providing an eventual end to the season`s first heat
wave.

Kimble

&&

.AVIATION...  (For the 12z TAFs through 12z Monday Morning)
Issued at 621 AM CDT Sun Jun 28 2026

Winds turn southerly today with some gusts to near 20KT during the
afternoon. VFR conditions will be widespread, though some
lingering IFR ceilings this morning will last longest at Quincy
before dispersing.

Kimble

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Heat Advisory from noon today to midnight CDT Thursday night 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 from noon today to midnight CDT Thursday
     night for Franklin MO-Jefferson MO-Saint Charles MO-Saint
     Louis City MO-Saint Louis MO-Sainte Genevieve MO-Warren MO.

IL...Heat Advisory from noon today to midnight CDT Thursday night 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 from noon today to midnight CDT Thursday
     night for Clinton IL-Madison IL-Monroe IL-Randolph IL-Saint
     Clair IL-Washington IL.

&&

$$

WFO LSX