073
FXUS63 KLSX 261036
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
536 AM CDT Wed Aug 26 2026

.KEY MESSAGES...

- Isolated to widely scattered showers and thunderstorms are expected
  along a cold front this afternoon/evening, mainly across
  south-central Illinois. A couple may be strong to severe with
  damaging winds the main threat.

- Near to slightly below normal temperatures are expected behind today`s
  cold front heading into the weekend before more summerlike
  heat returns Sunday into next week.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 318 AM CDT Wed Aug 26 2026

Weak low-level moisture convergence across the area has led to
some isolated rain showers across parts of southeast Missouri
and south-central Illinois. The latest RAP analysis shows the
south-central Illinois activity is likely being aided by the
approach of a weak midlevel shortwave trough as well. CAMs are
still all over the place through this morning, but it does look
like the very aggressive models (HiRes ARW, NSSL WRF) are too
early and too widespread/organized with convection. Reality will
most likely be closer to the quieter HRRR/FV3 CAMs, which show
some spotty showers/weak thunderstorms through mid morning. A
stronger storm is not out of the question given 1500+ J/kg of
MUCAPE and 30+ knots of effective shear on the latest
mesoanalysis, though that seems like an unlikely scenario at
this time. Small hail would be the main concern with anything
that develops through this morning.

Attention will then turn to a surface cold front moving southeast
out of the mid-Missouri Valley/Upper Midwest. This boundary looks a
bit quicker than it did 24 hours ago, and should approach central
Missouri into west-central Illinois just after midday. By early this
evening, the front is forecast to be just southeast of the I-44/I-55
corridors in Missouri and Illinois respectively. Convective coverage
along the boundary looks isolated to widely scattered, at best.
There is very weak mid/upper level forcing for ascent overhead, with
also weak surface convergence. Therefore, the expectation is for
only isolated to possibly widely scattered showers and thunderstorms
to develop mid to late afternoon, mainly across south-central
Illinois. This is where the surface convergence is slightly
stronger. The much better chance of showers and thunderstorms is
from far eastern Illinois into the Ohio Valley/Great Lakes. Another
area of stronger mid/upper level forcing and surface convergence is
ahead of a remnant MCV across the mid south. Our area will be
between these two more focused areas of convection. The environment
today likely would be supportive of a mixed mode of mainly pulse
convection, but also some multicellular clusters, and potentially
even a transient supercell, are also possible. Damaging winds are
the primary threat due to high DCAPE values courtesy of inverted-V
profiles. However, the very weak surface convergence does make this
threat quite conditional in our area.

Temperatures today are expected to warmup ahead of the cold front,
with some aid via compressional warming and downsloping off of the
Ozark Plateau. Highs in the upper 80s to near 90 degrees are favored
for most, though low 90s are most likely in/near the St. Louis metro
area.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Issued at 318 AM CDT Wed Aug 26 2026

(Thursday - Friday Night)

Dry weather with low humidity and near to slightly below normal
temperatures are forecast to end the work week thanks to a ridge of
high pressure moving into the mid-Mississippi Valley. Highs each day
are expected to be in the mid 80s, with lows in the upper 50s to mid
60s.


(Saturday - Tuesday)

Ensemble guidance is in good agreement that the mid/upper level
ridge will shift back eastward by late this weekend. This portends
to a return to summertime heat beginning Sunday. Dewpoint (humidity)
levels though look slower to increase, and likely will stay
relatively low until Tuesday. This is when dewpoints may pool closer
to a cold front that may get hung up just to our north. Heat index
values are more likely to approach or exceed the century mark by
Tuesday. All in all, this looks like a fairly typical late August
heat where dewpoints (relative humidity) levels are quite a bit
lower than early to mid summer levels.

&&

.AVIATION /06Z TAFS THROUGH 12Z THURSDAY/...
Issued at 534 AM CDT Wed Aug 26 2026

Thunderstorms across southeast Missouri will continue to move
off to the southeast and stay away from area terminals. A cold
front is forecast to move through from northwest to southeast
later today, with winds veering from the south/southwest to the
northwest behind the boundary. Additional showers and
thunderstorms are possible along this front this
afternoon/evening, though mainly across south-central Illinois.
Therefore, kept TAFs dry/VFR through tonight. I cannot rule out
some river valley fog late tonight, but that will depend on
clearing. Given some uncertainty, elected to not add to
SUS/JEF/CPS at this time, but it is something to watch going
forward.

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.

&&

$$

SHORT TERM...Gosselin
LONG TERM...Gosselin
AVIATION...Gosselin