814
FXUS63 KLSX 291946
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
246 PM CDT Fri Aug 29 2025

.KEY MESSAGES...

- Mostly dry conditions will continue through this weekend.
  Relatively cool temperatures will take hold early next week.


&&

.SHORT TERM...  (Through Late Saturday Night)
Issued at 245 PM CDT Fri Aug 29 2025

A backdoor cold front is pushing west through portions of west and
south-central Illinois before stalling near the Mississippi River
overnight. Along it, there is just enough surface convergence and
instability to promote isolated showers this afternoon. These
showers will be the most noticeable aspect of the front`s passage.
Its small influence on the temperature forecast will come tonight
when drier air infiltrates portions of south-central Illinois and
creates a lower floor for nighttime lows. This area will fall into
the low-50s with areas to the west remaining in the upper 50s to 60
degrees. The cool start to the morning will cause high temperatures
to lag behind as well, with south-central Illinois climbing into the
low 80s opposed to the mid to upper 80s forecast south of I-70.
Isolated showers are possible along the stalled front again
tomorrow afternoon as mid-level vorticity maxima eject into the
area ahead of a shortwave in the central Plains. Showers will be
focused mostly in northeast Missouri and west-central Illinois
where mid-level support and surface convergence will be strongest.

Jaja

&&

.LONG TERM...  (Sunday through Next Friday)
Issued at 245 PM CDT Fri Aug 29 2025

The aforementioned shortwave trough in the central Plains will
meander southeast into western Missouri by Monday. Cyclogenesis will
occur in response to the shortwave and pull low to mid-level
moisture in the vicinity of the low, with most of the low-level
moisture remaining very close to the low`s center. This means that
as the core of the system passes to our southwest, most moisture
return and as an extension rain chances will stay out of our area.
LREF probabilities aren`t excited about any given location seeing
measurable rain, with only a ~40% chance at KCOU for any 6 hour
period through next week and a ~50% chance for KFAM for the same
period. Locations that do see rain won`t see much. Probabilities of
0.10" of rain at any location for the next week don`t top 35%.

A deepening longwave trough in south-central Canada will carry the
shortwave and rain chances associated with it out of the Mid-
Mississippi Valley by Tuesday night/Wednesday. However, it will
usher in its own chance for rain on Wednesday along a very potent
cold front for early September. The biggest impact expected with
this cold front is a stark cooldown for late next week. There is
high confidence in this forecast, as even the 75th NBM percentile
high for Thursday is below average for this time of year. How cool
we`ll be is still uncertain as characterized by an interquartile
spread of 7 degrees (an improvement from yesterday`s 10 degree
spread) on Thursday, but regardless it`ll still be relatively
pleasant. Temperatures begin to moderate again on Friday, but not
fast enough to avoid a couple of days of pleasant weather.

Jaja

&&

.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1157 AM CDT Fri Aug 29 2025

Dry and VFR conditions with light winds will prevail through the
TAF period. There is a small chance that terminals in Illinois see
pinpoint showers this afternoon, but chances are too low to
mention in the TAFs.

Jaja

&&

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

$$

WFO LSX