378
FXUS63 KLSX 010740
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
240 AM CDT Wed Jul 1 2026

.KEY MESSAGES...

- Hot and humid conditions continue through Friday and potentially
  Independence Day.

- Scattered showers and thunderstorms become more common this
  weekend.

&&

.SHORT TERM... (Through Thursday)
Issued at 133 AM CDT Wed Jul 1 2026

The ridge that has brought our summer heat has nudged a bit
further east this morning, roughly centered near Knoxville, TN.
It`s slightly weaker today than yesterday, but its influence has
expanded into the Northeast US while maintaining influence through
our region. Looking at the trends in regional upper air
observations over the last few days we can see that the subsidence
inversion that has served as an effective cap has gradually
lowered. We were able to mix into it somewhat yesterday, and we`ll
likely do so more fully today. The result will be temperatures today
near or perhaps a degree warmer than they were yesterday. Just
like yesterday, as we mix deeper we will be able to mix down some
lower dewpoints during peak heating, helping to cut back on the
oppressive humidity just a bit. We`ll still reach dangerous heat
index levels of 100 to locally 110 degrees on the 4th day of this
air mass.

Thursday, day 5 of this air mass, will see the cap fully break
down allowing access to all the instability built up by this warm
and humid air mass. However with a lack of forcing we`ll likely
see only isolated thunderstorms bubbling up in the afternoon. With
virtually no shear, storms will be of the pulse variety producing
locally heavy downpours and gusty winds, but not a widespread
severe weather or flood threat. It will also take until the heat
of the day for these to begin to bubble up, so any heat relief
will be localized, temporary, and too late to avoid another day of
100 to locally 110 degree heat index values.

Kimble

&&

.LONG TERM... (Thursday Night through Monday)
Issued at 133 AM CDT Wed Jul 1 2026

Friday, day 6 of this air mass, will see further weakening and
broadening of the ridge. We`ll still be hot and humid, but a
degree or two cooler than our peak a couple of days earlier.
Afternoon thunderstorms will again be possible, though they`re
likely to be more focused with a shortwave trough moving through
Iowa and northern Illinois. Still, though, isolated storms are
possible locally especially with any leftover outflow boundaries
from anything that may have formed on Thursday.

By Saturday, Independence Day, ridging will be building to our
west while the ridge to our east continues to weaken. We`re left
in relative troughing in between with a better chance of showers
and thunderstorms as a result. The air mass will still be humid,
but the potential for clouds to limit heating makes the
temperature forecast more uncertain. If we see less clouds and
convection then the holiday could be nearly as hot as Friday, but
if there`s more clouds around it would be a few degrees cooler.
An eventual extension of some level of heat headline may be needed
at some point.

As ridging reorganizes to our west, we get in more of a
northwesterly upper level flow across our area. Guidance varies on
how to handle things, with some sources developing a more
definitive trough and a cold front pushing into our area. Others
maintain more influence from the ridge. The result is greater
chances of thunderstorms and more uncertainty on temperatures. The
likelihood of extreme heat, however, is lower after Saturday.

Kimble

&&

.AVIATION...  (For the 06z TAFs through 06z Wednesday Night)
Issued at 1016 PM CDT Tue Jun 30 2026

Dry and VFR conditions are expected through the period with south
to southwesterly winds at 5 to 10 knots.

Britt

&&

.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