172
FXUS63 KLSX 111057
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
557 AM CDT Mon Aug 11 2025

.KEY MESSAGES...

- Seasonably warm and humid weather will continue this week with
  highs near normal in the mid 80s to around 90 in most locations.
  There will be a chance for thunderstorms, primarily in the
  afternoon and evening at least through Wednesday or Thursday.

- Temperatures are expected to warm above normal by the end of the
  week in to the weekend.


&&

.SHORT TERM...  (Through Late Tonight)
Issued at 328 AM CDT Mon Aug 11 2025

A mid/upper level trough remains over the Great Plains today. The
surface front is difficult to find in surface obs due to ongoing
convection and old outflows.  The low level forcing for convection
will therefore weak and diffuse today, and will remain so through
tonight.  This will make the timing and location of convection
difficult to forecast through the period.  Regardless, the GFS and
RAP show up to 2000-2500 J/Kg MLCAPE building up across Missouri
into Illinois this afternoon, and both models produce precip during
the late afternoon and evening. Most CAMs also develop thunderstorms
during the mid to late afternoon, and some have convection
persisting through much of the night. Therefore I feel that some
level of chance PoPs are warranted through the period, though I`m
not confident enough to go higher than 50% in any given location or
time frame.

Carney

&&

.LONG TERM...  (Tuesday through Sunday)
Issued at 328 AM CDT Mon Aug 11 2025

The Great Plains trough finally starts moving east late tonight and
Tuesday.  The associated cold front will drift into Missouri and
Illinois Tuesday morning providing some low level forcing for
additional thunderstorm development.  RAP/GFS both develop precip
ahead of the front, though it doesn`t look particularly organized.
Both models develop around 2500 J/Kg MLCAPE during the afternoon but
the deep layer shear remains weak at 20kts or less.  Additionally,
there`s some weak CINH during the afternoon and convergence along
the front is not very strong.  Latest CAMs only show
scattered/disorganized convection Tuesday afternoon.  Will therefore
increase PoPs in the chance range through Tuesday afternoon.
Instability falls off quickly in the evening and CINH increases so
convection should weaken rapidly during the evening.

Upper level ridging builds across the Plains and Midwest through the
remainder of the week.  Typical summertime temperatures in the mid
80s to around 90 are expected with a 20-30 percent chance for
afternoon and evening thunderstorms, mainly along and south of I-70.
The ridge continues to build overhead next weekend causing
temperatures to rise back above normal in the low to mid 90s.

Carney

&&

.AVIATION...  (For the 12z TAFs through 12z Tuesday Morning)
Issued at 551 AM CDT Mon Aug 11 2025

There is a chance for thunderstorms across most of the area today
and tonight. The highest chance will be late this afternoon and
evening across parts of central and northeast Missouri into west
central Illinois. Any thunderstorm will be capable of reducing the
visibility to 2SM or less in heavy rain, and some strong wind
gusts to 30-40kts are also possible. Some patchy fog is also
showing up in observations this morning across central and
northeast Missouri into west central Illinois, and there are some
indications that this will lift into an MVFR ceiling for a brief
period this morning before lifting further and scattering.
Elsewhere and otherwise, VFR flight conditions with light
southerly flow is expected to prevail.

Carney

&&

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

$$

WFO LSX