826
FXUS63 KLSX 041033
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
533 AM CDT Thu Jun 4 2026

.KEY MESSAGES...

- Temperatures will be seasonably warm and humidity will become
  increasingly summer-like today into the weekend.

- There is a slight chance for showers and thunderstorms this
  afternoon into early evening across parts of central and
  northeast Missouri. The chance for showers and storms spreads to
  much of the area Saturday, but Sunday through Tuesday will see
  the highest likelihood for rain.


&&

.SHORT TERM...  (Through Late Friday Afternoon)
Issued at 344 AM CDT Thu Jun 4 2026

A mid-upper level short wave will move from the Plains into western
Missouri today.  There is a weak low level reflection of the wave
over the Great Plains this morning, and the tightening pressure
gradient between it and the sprawling high over the eastern U.S.
will produce increasing southerly flow across the Mid Mississippi
Valley today.  The southerly flow will bring increasing amounts of
low level moisture back to the region today, and the wave aloft will
produce broad synoptic scale lift over the eastern Plains into parts
of the Midwest.  This will allow the convection which is ongoing
over the Plains this morning to spread east through Friday.  Current
thinking is that the most if not all of the forecast area will
remain dry at least through late tonight.  A few CAMs show isolated
showers over parts of central and northeast Missouri this afternoon
into early evening, so a 20 percent chance for precip seems
appropriate.  Have kept the remainder of the CWA dry until late
tonight and Friday when the short wave finally moves into eastern
Missouri and Illinois.  Even so, models are not showing the presence
of any synoptic scale low level focusing mechanisms on Friday, so
areal coverage of convection looks scattered at best.  CAMs agree
with this idea so have limited PoPs to 20-40 percent through Friday
afternoon in most locations.  The deterministic RAP and GFS as well
as the HREF And REFS ensembles show CAPE values exceeding 2000 J/Kg
across northeast Missouri into west central Illinois Friday
afternoon, however deep-layer shear values generally do not exceed
25kts.  A few strong storms will therefore be possible but current
thinking is that storms will generally stay below severe thresholds.
Instability drops quickly to the southeast, and also diminishes
after sunset. The southerly flow will also help temperatures rise
a few degrees into the mid and upper 80s today and Friday,
although the increased humidity will probably be more noticeable
than the warmer temperatures.

Carney

&&

.LONG TERM...  (Friday Night through Wednesday)
Issued at 344 AM CDT Thu Jun 4 2026

The weather will remain unsettled this weekend into next week as a
weak cold front drifts into northern Missouri Saturday, and then an
upper low moves from Texas and Oklahoma into the east central Plains
on Sunday and continues drifting northeast across the Midwest Monday
into Tuesday. The front on Saturday will provide a low level focus
for convection during the afternoon. However, short wave ridging
ahead of the upstream upper low will produce decent over the area
which may have a limiting effect on convective development.
Additionally, the position of the front is uncertain and may stay
farther north across Iowa and northern Illinois. These uncertainties
yield only a 20-30 percent chance for showers and thunderstorms
Saturday.

The best chance for rain through the period will be Sunday through
Tuesday as the upper level trough moves from the Plains across the
Midwest.  Models suggest that convection will flare up each
afternoon due to daytime heating and broad synoptic scale lift
provided by the wave.  Despite CAPE values exceeding 2500 J/Kg at
times during this period, 0-6km shear remains below 30kts, and
doesen`t even exceed 15kts at times.  While current indications are
that thunderstorms are likely Sunday through Tuesday, and that some
could be strong due to the relatively high instability, the lack of
strong shear should limit the threat for severe storms. Temperatures
through the period will feel very summer-like with highs in the
upper 80s to low 90s and lows generally in the mid 60s to low 70s.

Carney

&&

.AVIATION...  (For the 12z TAFs through 12z Friday Morning)
Issued at 528 AM CDT Thu Jun 4 2026

VFR flight conditions and southerly winds are expected to prevail
through the period. An isolated shower or thunderstorm is possible
this afternoon and early this evening across parts of central and
northeast Missouri. Showers and thunderstorms are possible again
very late in the period around 12Z Friday morning in northeast
Missouri.

Carney

&&

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

$$

WFO LSX