561
FXUS63 KLSX 090920
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
420 AM CDT Wed Jul 9 2025

.KEY MESSAGES...

- Seasonably warm temperatures are expected into the weekend with
  the warmest day on Friday.

- After a mainly dry day today, the chance for showers and
  thunderstorms will increase over the weekend.


&&

.SHORT TERM...  (Through Late Thursday Afternoon)
Issued at 418 AM CDT Wed Jul 9 2025

Latest surface analysis is showing high pressure centered over
northern Missouri with a stationary front extending from the Great
Lakes into the northern Plains. The high clouds were in the process
of clearing out over the area revealing valley fog in the nighttime
microphysics channel.  Expect this fog to stick around through mid
morning before it will dissipates.  Then expect a mainly dry day as
the HREF is showing the upper trough slowing moving off to the east
with forecast soundings mainly capped over the area today.  The HREF
members are mainly dry into tonight before some members show a MCS
developing over eastern Nebraska/west Iowa late tonight on the nose
of a nocturnal low level jet.  This MCS will eventually move along
the front and into northeast Missouri and west central Illinois by
tomorrow morning. The chance for showers and thunderstorms will
linger along the front over the northern half of the CWA into
Thursday afternoon where MLCAPES will be in the 1500-3000 J/kg. Deep
layer shear will only be in the 15-30 knot range limiting the severe
weather threat.

High temperatures the next two days will be seasonably warm in the
middle 80s to around 90 degrees as 850 mb temperatures are in the 15-
20C range.

Britt

&&

.LONG TERM...  (Thursday Night through Tuesday)
Issued at 418 AM CDT Wed Jul 9 2025

The upper pattern from late this week into early next week will
continue to have Missouri and Illinois sitting on the southern edge
of the active westerlies with large highs over the southern CONUS.
The global models are highlighting a series of troughs moving
through the upper flow with the most LREF members producing rain
Friday night into Saturday and again on Tuesday.  While it will not
be raining all of the time, model PWATS AOA 2" suggest the potential
for some locally heavy rainfall over the weekend.

The warmest day still looks to be Friday with highs in the low to
mid 90s and heat indexes around 100 degrees.  Temperatures through
the weekend into next week look close to July normals ranging from
the mid 80s to around 90 degrees.

Britt

&&

.AVIATION...  (For the 06z TAFs through 06z Wednesday Night)
Issued at 932 PM CDT Tue Jul 8 2025

The main concern for overnight is fog potential. Continue to think
that the best chances are in central Missouri as both KCOU/KJEF
did receive some rain and at least some partial clearing is likely
overnight. IFR visibilities are expected at both of these
terminals late tonight into early Wednesday morning. Elsewhere,
the fog potential is a lower due to lingering cloud cover. KSUS
may at least have a brief period of MVFR visibilites as some late
partial clearing is expected before daybreak.

Any fog should quickly lift/dissipate by 1300 UTC, with dry/VFR
conditions and light/variable winds expected through Wednesday
evening. Cannot completely rule out a rogue shower/weak
thunderstorm on Wednesday afternoon, but the coverage continues to
look much too low to add any VC or PROB30 mention to any of the
terminals at this juncture.

Gosselin

&&

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

$$

WFO LSX