591
FXUS63 KLSX 110836
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
336 AM CDT Thu Jun 11 2026

.KEY MESSAGES...

- Scattered strong to severe thunderstorms capable of tornadoes, large
  hail, and damaging wind gusts are expected this afternoon and
  evening.

- After another warm and muggy day today, relatively cooler
  temperatures are expected through early next week.

- There is a low chance for strong to severe thunderstorms on
  Saturday.


&&

.SHORT TERM... (Through Friday Night)
Issued at 333 AM CDT Thu Jun 11 2026

Water vapor imagery this morning shows a shortwave digging into the
Central Plains. Ahead of that, a diffuse low-level jet is feeding
convection along a stalled cold front across the Midwest. Given the
front has stalled and the low-level jet will become increasingly
focused west-northwest of the CWA, convective coverage is expected
to gradually wind down through the pre-dawn hours. Chances for
scattered showers and weak thunderstorms will be primarily confined
to portions of Illinois north of I-70 where low-level flow interacts
with outflow boundaries.

Through the day today, deep south-southwesterly flow will continue
advecting warm air into the CWA south of the cold front, leading to
another muggy day. There is minor concern that dew points pooling
ahead of the front will give humidity levels enough of a boost to
push areas above a 105 degree heat index; however, another day of
southwesterly surface flow is expected to mitigate this threat via
downsloping effects from the Ozarks.

Dew points in the low to mid 70s will yield SBCAPE values of at
least 3,000 J/kg ahead of the front that will begin pivoting east-
southeastward as the aforementioned shortwave moves through the
Northern Plains into the Upper Midwest. The surging of the front
paired with the lift from the shortwave is expected to initiate
convection during the early afternoon across north-central Missouri
and southern Iowa. Given the amount of instability present,
updrafts will rapidly intensify, with additional updrafts expected
to develop southward along the front. As these storms move into the
CWA, deep-layer shear magnitude and vector orientation will favor
supercells capable of damaging wind gusts, large hail, and tornadoes
across northeastern Missouri and west-central Illinois along and
north of Hwy 36/I-72. Further south, deep-layer shear will decrease
and become increasingly parallel to the front, with a threat of
multicellular clusters posing mainly a damaging wind threat. With
forcing being tied to and immediately ahead of the front, there is
concern over updrafts congealing and/or being undercut by the front.
This would lead to a lower tornado and large hail threat, though if
storms are able to remain more discrete and ahead of the front, a
greater tornado and hail threat will be realized.

The front and associated convection will clear the CWA to the
southeast around midnight, with a cooler airmass advecting into the
region. This will bring a notable change to our weather on Friday,
with seasonable temperatures, lower humidity, and mostly clear skies
expected areawide.

Elmore

&&

.LONG TERM... (Saturday through Wednesday)
Issued at 333 AM CDT Thu Jun 11 2026

Early on Saturday, the area of high pressure at the surface
responsible for Friday`s weather will shift eastward, allowing for
low-level moisture to stream back into the Plains and Middle
Mississippi Valley. This will be occurring ahead of another
shortwave digging into the Midwest, sending yet another cold front
through the region. At this lead time, there are still notable
differences among guidance in the degree of moisture return and
local FROPA. For locations within the warm sector, deep-layer shear
of roughly 40 kts will support supercells capable mainly of large
hail and damaging wind gusts. A majority of guidance has low-level
wind shear too weak for a notable tornado threat. Even if severe
thunderstorms aren`t realized in the CWA, this will serve as another
chance for rain across the area - mainly late Saturday into early
Sunday.

In the wake of Saturday`s front, ensembles support daily
temperatures at or just below climatology as upper-level troughing
remains in place over the eastern CONUS through at least the middle
of the week. The general positioning of the trough among
deterministic guidance and ensemble clusters will open the CWA to
northwest-flow disturbances, but at this lead time, a majority of
ensemble guidance keeps the area dry through the first half of the
week.

Elmore

&&

.AVIATION...  (For the 06z TAFs through 06z Thursday Night)
Issued at 1125 PM CDT Wed Jun 10 2026

Area of showers and thunderstorms across northeast Missouri and
west central Illinois will continue to bring MVFR conditions to
UIN through 08Z as it moves southeast. I now expect this area to
stay out of the COU/JEF, but it may still affect the St. Louis
area terminals, so have kept a PROB30 group going until 08Z. Then
mainly dry weather and VFR conditions are expected through 18Z
tomorrow with an increasing chance for showers and thunderstorms
along a cold front tomorrow afternoon and evening that will move
from northwest to southeast across the area. The best timing for
thunderstorms at UIN/COU/JEF will be between 21-01Z and at the
STL/SUS/CPS between 00-04Z on Thursday evening. The strongest
storms will reduce visibilities and ceilings to MVFR/IFR
conditions and will also have the potential to produce hail and
wind gusts to 35 knots. Winds will gust into the 25 to 30 knot
range on Thursday afternoon outside of thunderstorms.

Britt

&&

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

$$

WFO LSX