272
FXUS63 KLSX 301936
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
236 PM CDT Tue Jun 30 2026

.KEY MESSAGES...

- Dangerous heat and humidity are expected through at least Friday,
  with confidence low to medium in these conditions continuing
  through the holiday weekend.

- The threat of isolated to scattered showers and thunderstorms
  gradually increases Thursday through Sunday.


&&

.SHORT TERM...  (Through Late Wednesday Night)
Issued at 232 PM CDT Tue Jun 30 2026

Highly amplified upper-level ridging continues to encompass much of
the eastern CONUS per water vapor imagery, with little to no change
in the regional surface pattern from days past. Surface winds are
more southwesterly today than as of late, which is expected to give
temperatures a minor boost this afternoon thanks to downsloping
off of the Ozarks. However, this will also nudge dew points down
slightly, making it a wash when it comes to area heat index
values. Values around 105 degrees are expected this afternoon.
With the upper-levels and surface pattern remaining relatively
stagnant through tomorrow, similar conditions are expected.

Elmore

&&

.LONG TERM...  (Thursday through Next Tuesday)
Issued at 232 PM CDT Tue Jun 30 2026

The consensus among both deterministic and ensemble guidance is that
the upper-level ridge will gradually breakdown and flatten through
the weekend. In response, temperatures at 850mb will slowly cool,
with surface temperatures following a similar trend. With the low to
mid-level temperatures cooling, capping will be less of an issue,
allowing for daily chances for convection to return starting on
Thursday. However, the convective signal in courser guidance
Thursday-Saturday may be too strong and the result of the guidance
over-convecting. The 06z and 12z GFS are examples of this occurring
over our CWA, and this is most likely over-inflating the PoPs from
the NBM especially on Friday and Saturday. A majority of
deterministic soundings show surface temperatures coming within a
degree or two of convective temperatures through this portion of the
period, and when coupled with the cooling aloft, does support a low
chance for isolated to scattered convection during peak heating
Thursday-Saturday. More locations will remain dry than see
rainfall each afternoon. Rain chances increase Saturday night
through Monday as a weak front sinks into the Middle Mississippi
Valley; though, details on the timing of this front are highly
variant among guidance thanks to weak forcing from quazi-zonal
flow aloft.

With the ridge weakening and low to mid-level temperatures cooling,
we`ll experience a gradual reprieve from the heat as we move into
the holiday weekend and early next week. By how much and how quickly
still remains uncertain, as the degree to which the ridge weakens
varies enough that the interquartile range of ensemble guidance is 5
degrees for high temperatures Saturday onward. While this isn`t a
large spread for this lead time, it is enough to still question
whether heat headlines will need to be continued into the weekend.
Even if heat headlines aren`t needed, conditions will still be very
summer-like, with air mass convection providing a low chance for
localized, brief breaks from the heat. The aforementioned front, how
quickly it moves into and through the area, increases uncertainty in
high temperatures even more for Sunday through Tuesday.

Elmore

&&

.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1236 PM CDT Tue Jun 30 2026

Confidence is high in dry and VFR flight conditions through the
period at all local terminals.

Elmore

&&

.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