832
FXUS63 KLSX 241917
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
217 PM CDT Mon Aug 24 2026

.KEY MESSAGES...
- Seasonably warm temperatures in the 80s will continue this
  week. There is a chance for thunderstorms Wednesday ahead of a
  weak cold front.

&&

.SHORT TERM /THROUGH TUESDAY/...
Issued at 204 PM CDT Mon Aug 24 2026

Today: Surface high pressure was centered over western Illinois
early this morning and is now currently near the Illinois/ Indiana
border. Thunderstorms over Nebraska and Iowa from this morning
have considerably weakened as they move across eastern Missouri.
No precipitation is expected in the St. Louis area, only mid
and high clouds. Temperatures have also been a couple of degrees
cooler today than expected given the widespread cloud cover.
Expect highs to be mostly be in the upper 70s to around 80
degrees.

Tonight: Mid and high cloud debris will start to lose cohesion,
however latest forecast soundings do show pesky 8kft deck
clouds remaining through the overnight hours. The clouds and
retreating high pressure will make lows 10 to 15 degrees warmer
Tuesday morning than was the case this morning (Monday).

Tuesday: Surface high pressure will be located over Ohio as the
closed upper level low south of the James Bay opens up and heads
east. At 850 mb, a warm front will surge northeast with temperatures
surging from 14 degrees C to 18 degrees C. This will translate to
surface highs warming into the mid to upper 80s Tuesday
afternoon.

&&

.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
Issued at 204 PM CDT Mon Aug 24 2026

Wednesday: An area of mid level low pressure will move east
across the northern Great Lakes with a cold front approaching
the area from the northwest. In the upper levels of the
atmosphere a dual jet streak will elongate over Iowa, Missouri,
Illinois, and Indiana. The first jet streak appears to be
associated with the long wave trough axis centered across the
central United States, while the second jet streak is rounding
the top of an amplifying ridge over the Rocky Mountains. This is
an interesting setup, as forecast soundings do show some
capping in place with the primary forcing for ascent well
northeast of the area. However, the surface boundary coupled
with the 250 mb jet streak might provide just enough lift for
thunderstorms. The latest run of the NBM has 10 - 20% PoPs
across the area, with LREF PoPs remain consistently higher (50 -
70%). Limiting the QPF on the LREF to 0.05" though reduces the
PoPs to 30 - 40%). Looking at forecast soundings, there is not
only weak capping in place but a skinnier CAPE. This makes the
lower QPF footprint understandable from a ensemble perspective
(most guidance likely not initiating thunderstorms while some
are). Ahead of the cold front, CAPE values rise to around 2000
J/kg, with SFC to 6 km shear values around 30 kt. If updrafts
become robust enough to penetrate the capping inversion and
drier air, locally damage wind gusts and severe hail could be
possible. As such, SPC has our far northeastern zones in a
marginal risk of severe weather.

Thursday - Sunday: The surface cold front from Wednesday will clear
Missouri and Illinois with seasonable temperatures and
dewpoints expected through Friday (no precipitation is
forecast). By Friday, the anticyclonic flow that was over the
Rocky Mountains will start to nudge east. As such, temperatures
are expected to warm back up into the 90s for Saturday and
Sunday. Spread on both the LREF and NBM is around 5 degrees with
the WPC Cluster Analysis showing a good amount of dispersion
between the GEFS, GEPS, and EPS. All of this being said,
precipitation is generally not expected Friday through Sunday
with a gradual warming trend forecast.

&&

.AVIATION /06Z TAFS THROUGH 12Z TUESDAY/...
Issued at 553 AM CDT Mon Aug 24 2026

All TAF sites are currently VFR this afternoon with weakening
showers currently over northeastern Missouri. Latest observed
ACARs soundings shows substantial dry air in the 800 to 900 mb
layer with a rapidly weakening low level jet. As such, no
impacts to the terminals are forecast (except a SCT to BKN 7 - 8
kft deck).

Tonight, surface high pressure will center near the Ohio/
Indiana border with light to variable southeast winds across the
terminals. Cloud cover from this afternoon is forecast to mostly
remain in place which makes the chance of morning fog less
likely.

&&

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

&&

$$

SHORT TERM...BAH
LONG TERM...BAH
AVIATION...BAH