Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

578
FXUS63 KLSX 301127
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
627 AM CDT Tue Jun 30 2026

.KEY MESSAGES...

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

- Chances for scattered showers and thunderstorms increase this
  weekend.


&&

.SHORT TERM...  (Through Late Tuesday Afternoon)
Issued at 215 AM CDT Tue Jun 30 2026

A 596dm ridge at 500MB is nearing its peak intensity and centered
roughly over Nashville, TN this morning. Its influence is still
felt across our region. In fact, today may well be the hottest
day of this air mass, with temperatures a couple of degrees hotter
than yesterday, in the mid to upper 90s, about 5 to 8 degrees
above average. Continued high humidity (dewpoints 7 to 10 degrees
above average) will contribute to another day of heat index values
in the 100 to 110 degree range. A stout capping inversion at
about 850MB evident on regional upper air observations will
suppress any attempts at convection this afternoon. It also means
that if we do warm a few degrees over yesterday, we`ll likely mix
down a bit drier air from within this inversion. The net result
will be similar heat index values to yesterday. The decision was
made to upgrade the rest of the forecast area to an Extreme Heat
Warning. Regardless of the headline, the message is the same: this
heat will be dangerous for those spending prolonged periods
outdoors or without access to a place to cool down.

Kimble

&&

.LONG TERM...  (Tuesday Night through Sunday)
Issued at 215 AM CDT Tue Jun 30 2026

The ridge nudges a bit further east Wednesday and especially
Thursday, though its influence remains strong over our region.
We`ll see similar levels of heat and humidity with heat index
values of 100 to 110 degrees. However, we do lose the capping that
prevented convection earlier in the week. So by Thursday and
especially Friday we`ll likely see a few scattered showers and
thunderstorms popping up during the heat of the day. In fact, some
deterministic guidance continues to show subtle troughs rotating
around the decaying ridge which lead to pockets of enhanced
convection lifting through our region. These storms will be of the
pulse variety, with little to no wind shear available. Thus their
impact will primarily be brief downpours, perhaps some locally
gusty winds, but otherwise have little effect on the heat and
humidity. The Heat Warning continues through Friday.

The ridge begins to reorganize this weekend, reforming to the
west near the Rocky Mountains. In between, most guidance is
showing some degree of troughing and potentially even a cold front
dropping into our region. This increases the chances for showers
and thunderstorms and also increases the uncertainty on the
continued heat heading into Saturday (Independence Day) and
Sunday. We still expect it to be hot and humid, but there`s the
potential that it will be closer to normal for July and not quite
the extreme levels we see earlier in the week. Subsequent heat
headlines of some form may be needed once confidence improves.

Kimble

&&

.AVIATION...  (For the 12z TAFs through 12z Wednesday Morning)
Issued at 626 AM CDT Tue Jun 30 2026

VFR conditions continue with a few passing high clouds, perhaps a
few cumulus in the afternoon. Winds remain out of the SSW just a
bit lighter than they were yesterday.

Kimble

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Extreme Heat Warning until 10 PM CDT Friday for Audrain MO-Boone
     MO-Callaway MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO-
     Iron MO-Jefferson 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 Charles MO-Saint Francois MO-
     Saint Louis City MO-Saint Louis MO-Sainte Genevieve MO-
     Shelby MO-Warren MO-Washington MO.

IL...Extreme Heat Warning until 10 PM CDT Friday for Adams IL-Bond IL-
     Brown IL-Calhoun IL-Clinton IL-Fayette IL-Greene IL-Jersey
     IL-Macoupin IL-Madison IL-Marion IL-Monroe IL-Montgomery IL-
     Pike IL-Randolph IL-Saint Clair IL-Washington IL.

&&

$$

WFO LSX