668
FXUS63 KLSX 071128
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
628 AM CDT Sun Jun 7 2026

.KEY MESSAGES...

- Scattered showers and thunderstorms capable of locally heavy
  rainfall are expected today and tomorrow across the area.

- This afternoon, thunderstorms will be capable of isolated instances
  of damaging wind gusts across central and southeastern
  Missouri.

- Heat and humidity build into the region Tuesday through Thursday,
  with highs reaching the 90s and heat index values near 100
  degrees.


&&

.SHORT TERM... (Through Monday Night)
Issued at 239 AM CDT Sun Jun 7 2026

Water vapor imagery this morning shows a cutoff upper-level low
slowly moving east-northeastward across Kansas and Oklahoma. This
cutoff is providing weak lift that is pairing with a subtle low-
level jet to produce the ongoing showers across portions of western
and central Missouri.

As this cutoff continues its east-northeastward trajectory through
the day, instability will build over the Middle Mississippi Valley.
Both the 00z HREF and REFS show 1,500-2,000 J/kg of SBCAPE across
the CWA during peak heating; primarily focused over central and
southeastern Missouri. Here, deep-layer shear is progged to be
greater than it has been in days past, with guidance consensus
showing 25-30 kts across the same portion of the CWA. While the
instability and nebulous forcing from the cutoff will lead to a
threat of isolated to scattered showers and thunderstorms capable of
locally heavy rainfall this afternoon across the entire CWA, the
environment over central and southeastern Missouri will be
particularly favorable for isolated strong to severe thunderstorms.
The primary severe threat here is damaging wind gusts. Confidence is
low in severe-sized hail thanks to skinny CAPE profiles in the hail
growth zone noted in several deterministic soundings, and tornadoes
are not expected thanks to weak low-level shear. Convective coverage
and strength will diminish this evening with the loss of daytime
heating, though the nebulous forcing from the cutoff aloft will keep
the chance for isolated showers and weak thunderstorms going through
the overnight hours.

Tomorrow, the cutoff will begin to shear apart over the Middle and
Upper Mississippi Valley, with its southern portion slowly moving
into the Ohio Valley. With enough of the cutoff still overhead
through the day, nebulous lift paired with roughly 2,000 J/kg of
SBCAPE will produce another round of scattered showers and
thunderstorms. Despite an uptick in instability, deep-layer shear is
forecast to not be as robust compared to today. Therefore,
confidence is very low in a threat of severe thunderstorms, and we
will hold off on publicly messaging the SPC Day 2 Marginal.

Elmore

&&

.LONG TERM...  (Monday Night through Saturday)
Issued at 239 AM CDT Sun Jun 7 2026

The cutoff/shortwave that has been plaguing the area through the
weekend and early week period will be departing the Middle
Mississippi Valley eastward on Tuesday per guidance consensus. There
is a low chance (30%) that the wave will still be close enough to
the CWA during peak heating to produce isolated to scattered
convection across south-central Illinois.

The main story with the departing wave will be upper-level ridging
building into the Midwest, giving the region its first taste of
summer-like heat and humidity. Tuesday is expected to be notably
muggier than Monday, with ensemble high temperatures clustering
around 90 degrees. Confidence is increasing that this heat will peak
on Wednesday, though to what degree remains uncertain. Guidance
varies enough on the strength of the ridge against a trough moving
eastward across the central CONUS to produce a roughly 5-degree
spread between the 25th and 75th percentile of ensemble
temperatures. Relatively cooler solutions thanks to a stronger
trough would keep temperatures similar to those forecast on Tuesday,
while a stronger ridge will yield a several degree bump. The current
forecast/NBM continues to favor the latter solution, and this should
be seen as a reasonable worst-case scenario.

From Thursday through Saturday, guidance consensus is that the upper-
level trough expands eastward as it broadens, pushing the ridge
southward. A leading shortwave within the trough will send a cold
front through the Middle Mississippi Valley sometime late Thursday
or Friday. This front will bring an end to the forecasted heat as we
move into the weekend, with a majority of ensemble guidance
signaling a notable drop in temperatures.

Elmore

&&

.AVIATION...  (For the 12z TAFs through 12z Monday Morning)
Issued at 622 AM CDT Sun Jun 7 2026

Another round of scattered showers and thunderstorms is expected
across the region today, but confidence is low in specific timing
at each of the local terminals. There is a low chance for impacts
through much of the daylight hours today, with impacts from
showers and thunderstorms potentially continuing overnight at KCOU
and KJEF. MVFR stratus is expected tonight, though how low
ceilings get is uncertain. There is a very low chance that
ceilings could drop below 2kft at any of the local terminals.
Stratus that develops overnight is expected to lift and dissipate
tomorrow morning.

Elmore

&&

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

$$

WFO LSX