307
FXUS63 KLSX 072355
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
655 PM CDT Thu May 7 2026

.KEY MESSAGES...

- Showers and thunderstorms are likely on Friday afternoon and
  evening. A few strong storms are possible.

- Saturday will be warm and dry, but a cold front will move
  through Saturday night with another chance for rain.

- Cooler weather will return behind the front on Sunday.


&&

.SHORT TERM...  (Through Late Friday Night)
Issued at 233 PM CDT Thu May 7 2026

Quiet weather and warm south-southwest flow will continue tonight
under the influence of high pressure over the southern U.S.  This
will result in milder low temperatures in the upper 40s to low 50s
tonight.  Northwest flow across the nation`s mid-section will drag a
short wave into the Plains overnight, and into the Midwest on
Friday.  This wave will push a weak cold front south into Missouri
and Illinois on Friday afternoon.  CAMs develop a broken line of
showers and thunderstorms Friday afternoon ahead of the front, and
push the line southeast through the area by mid-late evening.
The GFS and RAP develop between 1000-1500 J/Kg of CAPE coincident
with 40-50kt 0-6km shear Friday afternoon across central and east
central Missouri where the convection develops. However, forecast
soundings continue to show tall and thin CAPE profiles which would
lead to weaker updrafts. Additionally, the upper quartile of CAPE
values forecast by the HREF is about 400-500 J/Kg lower than the GFS
and RAP.  The 90th percentile CAPE values are closer to the
deterministic GFS and RAP, so I continue to feel they are a "worst
case scenario". Regardless, a few strong to severe storms are
possible Friday afternoon/early evening mainly across central
Missouri if the greater instability forecast is realized.  Any
convection that develops should be through the forecast area by
midnight or shortly thereafter and the remainder of Friday night
looks dry and mild.

Carney

&&

.LONG TERM...  (Saturday through Next Thursday)
Issued at 233 PM CDT Thu May 7 2026

The weather pattern over the Midwest will continue to be
dominated by northwest flow aloft for Saturday through next
Thursday.  Several short waves will move across the area during this
period with the first will dig into the Mid Mississippi Valley on
Sunday, pushing a cold front ahead of it.  Guidance has been pretty
consistent in moving the front through Missouri and Illinois by
early Sunday morning with minimal instability ahead of it.  While
scattered showers and thunderstorms continue to be likely Saturday
night, particularly over northeast Missouri and west central
Illinois, the threat for severe storms looks very small due to the
lack of instability.  Northeast flow behind the front on Sunday keeps
temperature in the upper 60s to around 70.  Temperatures warm into
the 70s Monday as southerly flow returns due to a developing low
over the Great Plains.  Ensemble guidance continues to show a good
deal of variance in the forecast headed into midweek as two more
short waves pass over the Midwest.  The EOF patterns off the LREF
cluster analysis indicate uncertainty in both the speed and
amplitude of each wave so confidence in the forecast out beyond
Monday remains low.  Generally speaking however, temperatures are
forecast to be near to above normal in the 70s to low 80s, with
rain chances Tuesday and again Thursday.

Carney

&&

.AVIATION...  (For the 00z TAFs through 00z Friday Evening)
Issued at 638 PM CDT Thu May 7 2026

Mainly dry and VFR conditions are expected through 12Z. Then there
will be an increasing (30-50%) chance of showers over northeast
Missouri and west central Illinois on Friday morning including at
UIN where I have included a PROB30 group between 15-18Z. A better
(70-90%) chance for showers and a few thunderstorms will affect
central Missouri including at COU/JEF where I have included a FM
group starting at 19Z with a PROB30 group for TS. Farther east the
showers and thunderstorms won`t move into the St. Louis area
terminals until mid to late afternoon when I have stared the
FM/PROB30 groups for showers and thunderstorms. Any of the heavier
showers and thunderstorms will be capable of producing
MVFR/possible IFR ceilings and visibilities in heavy downpours
with best chance for any hail or wind gusts over 35 knots on
Friday afternoon and evening at COU/JEF.



Britt

&&

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

$$

WFO LSX