191
FXUS63 KLSX 010350
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1050 PM CDT Sun Aug 31 2025

.KEY MESSAGES...

- A low chance (15-30%) of rain will persist through early this
  week for central Missouri (Monday/Tuesday) and southeast
  Missouri/southwest Illinois (Tuesday).

- A potent cold front will bring the chance for showers and a low
  chance for thunderstorms to the area on Wednesday. Unseasonably
  cool temperatures will follow the front and last through next
  weekend.


&&

.SHORT TERM...  (Through Late Monday Night)
Issued at 145 PM CDT Sun Aug 31 2025

A slow moving mid-level shortwave over the central Plains is
ejecting vorticity lobes into our region. This has resulted in
increased cloud cover for much of the area and isolated to scattered
showers in western and central Missouri. Tomorrow`s forecast will be
a repeat of today`s in terms of sky cover and precipitation chances
(15 - 25% in central/northeast MO). In response to another day
without sun, temperatures will cool into the low-70s to low-80 for
highs on Labor Day. The lowest temperatures will be centered in
central and northeast Missouri where cloud cover will have persisted
for a longer time.

Jaja

&&

.LONG TERM...  (Tuesday through Next Sunday)
Issued at 145 PM CDT Sun Aug 31 2025

The aforementioned mid-level shortwave will pivot and weaken on
Tuesday, pushing rain chances from western Missouri into southern
Missouri and southwest Illinois. Latest deterministic model runs
have pulled this feature further south and are depicting a weaker
system than previously forecast. This translates to a drier forecast
(15 - 25%) for the locations south of I-44/I-64, though rain chances
weren`t that high to begin with. A more tangible potential for rain
and perhaps thunder exists along a cold front on Wednesday, though
dry air sandwiching the front will keep showers scattered at best.
LREF probabilities of measurable rainfall on Wednesday top out at
60% along the front with probabilities of 0.1" remaining under 30%.
Needless to say, the cold front won`t be providing drought relief,
and that will be the last chance of rain through at least next
weekend.

What the cold front will bring is a stark cooldown as 850 mb
temperatures dive into the single digits, within the 0.5th
percentile of climatology for early September. At the surface, high
temperatures will be relegated to the upper-60s north of I-70 and
the low-70s south of I-70. This will be a 10 to 15 degree contrast
from Wednesday`s pre-frontal warm-up into the low-80s.

Temperatures will begin to rebound on Friday, but a second cold
front will put a brief pause to any further warming. Deterministic
guidance shows at least moderate cold air advection following this
wave, leading to a cooler weekend than previously expected. The NBM
has been catching onto this in its last few runs, bringing high
temperatures down to around its 25th percentile for the 18z init.
This keeps the CWA almost solidly in the 70s for Saturday and Sunday
and drops lows into the 40s for most areas north of I-70 during the
same time period. If this comes to fruition, we`d be looking at 4
straight days with lows in the 40s for significant portions of the
forecast area (Thursday morning - Sunday morning). Though this isn`t
impactful to most, it`s still an impressive little streak given
we`ll have just exited August.

Jaja

&&

.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1047 PM CDT Sun Aug 31 2025

Only minor changes were made to this iteration of the TAF. VFR
conditions remain most likely to prevail throughout the period.
There remains a very conditional chance for a few showers at
primarily COU/JEF in the mid to late afternoon, but it remains
somewhat unlikely that terminals will be directly impacted, and
that flight categories will be reduced either by reduced
visibility from rainfall or lowering ceilings. Otherwise, winds
will remain light and east-northeasterly.

BRC

&&

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

$$

WFO LSX