353
FXUS63 KLSX 250806
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
306 AM CDT Tue Aug 25 2026

.KEY MESSAGES...

- Seasonable temperatures are expected through Saturday before
  summertime heat likely returns Sunday into early next week.

- Scattered showers and thunderstorms are forecast Wednesday
  afternoon/evening. A few of these storms may be strong to
  severe with damaging winds the main threat.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 306 AM CDT Tue Aug 25 2026

Weak low-level moisture convergence in parts of
central/southeast Missouri may yield a few "sunrise surprise"
showers early this morning, though most guidance keeps the area
dry. Any chance should quickly wane within a few hours after
sunrise as the low-level jet weakens. Dry weather is then
expected areawide for the rest of the day with variable
cloudiness. Temperatures are forecast to warm well into the 80s
by this afternoon, back closer to normal for late August and
quite a bit warmer than yesterday. Milder readings are also
forecast tonight due to increasing mid/high level cloudiness and
light southerly flow. Lows are forecast to only drop back into
the mid 60s to near the 70 degree mark.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Issued at 306 AM CDT Tue Aug 25 2026

(Wednesday - Wednesday Night)

Scattered showers and (elevated) thunderstorms are expected in
southeast Missouri Wednesday morning as a midlevel shortwave trough
moves across the area with weak low-level moisture convergence. This
activity should move south with time. While the low-level jet
abates, the midlevel wave may be strong enough to keep convection
going to near or just past midday. If that indeed happens, the
storms could become more surface based and pose a damaging wind
threat before they exit. There is low confidence in this happening
however.

A slow-moving cold front is expected to move through the area
Wednesday afternoon through the early overnight hours as a longwave
trough deepens across the Great Lakes. Large scale forcing for
ascent is not particularly strong during this time period, though
there is some weak diffluence aloft along with some cooling. Surface
convergence is also on the weak side along the boundary itself, but
overall lift is expected to be strong enough to overcome some
capping (CINH 50-100 J/kg) in place. The coverage of showers and
thunderstorms however may stay isolated to widely scattered right
near the front itself. The environment does not look particularly
favorable for organized convection, but there may be just enough
instability in the presence of moderately strong (~30 knots) deep-
layer shear to produce a couple of strong-severe storms capable of
producing 60 mph winds. The latest HREF shows some pockets of 40-
50+% probabilities for at least 25 knots of shear and SBCAPE of
1000+ J/kg near the boundary.


(Thursday - Saturday Night)

A period of near to below normal temperatures along with dry
conditions is forecast to end the week and start the weekend as a
surface ridge of high pressure settles into the mid-Mississippi
Valley. The coolest period of time is expected to be between
Thursday night and Friday night. Lows each night are expected to be
in the low to mid 60s each night, with some spots quite possibly in
the upper 50s. Highs on Friday should predominantly be in the mid
80s.


(Sunday - Monday)

All signs to a fast warmup to end the weekend into early next week
as the mid/upper level ridge amplifies and moves into the
Mississippi Valley. The air mass looks pretty warm with 850-hPa
temperatures likely above +20C (>90th percentile). Surface dewpoints
(relative humidity) levels also look to climb by early next week
into the low 70s (75th-90th percentile). High temperatures well into
the 90s seem quite plausible with heat index values potentially in
the 100-105F range at least for portions of the area. In other
words, while the calendar will turn to September next week, summer
may not be giving up its grip. There is more confidence in
increasing heat in southern sections of the area at this point in
time due to the likely position of the ridge across the mid south.
Across northeast Missouri and west-central Illinois, the spread in
high temperatures is higher due to at least some potential for a
frontal boundary to be in the area as well as "ridge-runners"/waves
of showers and thunderstorms.

&&

.AVIATION /00Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 938 PM CDT Mon Aug 24 2026

Confidence remains high in dry and VFR flight conditions through
the period at all local terminals. There is a very low chance of
patches of fog tonight but scattered cloud cover is expected to
greatly limit fog development.

&&

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

&&

$$

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