086
FXUS63 KLSX 190356
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1056 PM CDT Wed Jun 18 2025

.KEY MESSAGES...

- Severe thunderstorms remain possible this afternoon and
  evening, particularly over southeast Missouri and southwest
  Illinois.

- Heat index values may climb above 100 degrees starting Friday
  and last into early next week.


&&

.SHORT TERM...  (Through Late Thursday Night)
Issued at 221 PM CDT Wed Jun 18 2025

A mid-level shortwave trough is currently swinging through the mid-
Mississippi Valley, generating convection across northern Missouri
along the retreating edge of the surface low. This convection is
expected to slide southeast through the forecast, first encountering
a stable airmass underneath low level cloud cover across central and
northeast Missouri. This will cause the showers and thunderstorms to
weaken as they move through. However, southeast of the stable
airmass is an open cumulus field that is already destabilizing.
Additional shower and thunderstorm development is expected across
this area that extend along and south of I-70 during the evening,
however uncertainty remains in how widespread coverage will be.

Effective bulk shear is expected to wane to 25-30 kts as the trough
and low-level jet exit the forecast area this afternoon. This will
be enough to organize any thunderstorms in the open cumulus field. A
few thunderstorms could become strong to severe, capable mainly of
damaging winds given the dry low-levels and modest instability.
Convection will weaken and become elevated this evening as the near
surface layer stabilizes, further reducing the severe threat. Once
the cold front pushes through the forecast area, dry conditions and
a clear sky will prevail for the remainder of the evening.

A mid-level ridge will push into the mid-Mississippi Valley
Thursday, while southwesterly low-level flow will already be
established. The subsequent warm air advection will offset any
cooling that would have come from the post-frontal air. Temperatures
will peak in the 80s Thursday under a mostly clear sky.

Delia

&&

.LONG TERM...  (Friday through Next Wednesday)
Issued at 221 PM CDT Wed Jun 18 2025

Southwesterly mid-level flow will establish by Friday, while 850 mb
temperatures will surge into the upper teens to low 20s, favorable
for high temperatures in the 90s area wide. This, combined with
dewpoints in the 70s, will result in heat index values pushing 100+F
across much of the area Friday through at least Monday, including
the St. Louis metro. This is our first long duration heat event of
the year, and those without adequate shelter or cooling systems will
be at higher risk for heat related illnesses.

The center of the ridge will waiver between the mid-Mississippi and
Ohio River Valleys during the period, keeping the area dry through
at least the first portion of the work week. Precipitation chances
return to the forecast midweek, and if that rain materializes, will
help to knock temperatures down a few degrees.


Delia

&&

.AVIATION...  (For the 06z TAFs through 06z Thursday Night)
Issued at 1053 PM CDT Wed Jun 18 2025

Expect VFR flight conditions outside of isolated-widely scattered
convection. The convection is expected to move from central
Missouri to the east southeast into parts of southeast Missouri
through the overnight hours. A general weakening trend is also
expected with this area of storms. Expect isolated IFR visibility
in heavy rain, brief MVFR ceilings, and possibly some wind gusts
to 35-40kts with the strongest storms. Dry and VFR conditions with
light northwest winds are expected on Thursday.

Carney

&&

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

$$

WFO LSX