954
FXUS63 KLSX 311846
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
146 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 18z TAFs through 18z Monday Afternoon)
Issued at 1149 AM CDT Sun Aug 31 2025

Pesky showers will continue to percolate in central Missouri
through tomorrow morning, though plenty of dry time is expected.
Dry air from the east is undercutting these showers, so rain is
not hitting the ground underneath every signal on radar. Despite
this, rain making it to the ground is possible through this
afternoon, so I added PROB30s at KCOU and KJEF. Otherwise,
easterly winds will continue through the end of the TAF period.


Jaja

&&

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

$$

WFO LSX