668
FXUS63 KLSX 112245
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
545 PM CDT Sat Oct 11 2025

.KEY MESSAGES...

- Temperatures will run at or above climatological normals through the
  upcoming week.

- Mostly dry conditions are expected through the forecast period.



&&

.SHORT TERM...  (Through Late Sunday Night)
Issued at 135 PM CDT Sat Oct 11 2025

Upper-level flow over the Middle Mississippi Valley is northwesterly
per recent water vapor imagery. However, recent ACARS out of KSTL
and RAP Analysis show that low to mid-level flow is already
becoming east-southeasterly. This has further weaken last night`s
front, with temperatures across much of the area actually running
similar to or above values at this point yesterday.

Clear skies tonight will allow for some degree of radiational
cooling, but south-southeastelry winds may be a few mph stronger
than last night, limiting fog potential despite the cool
temperatures. Additionally, we will not have the benefit of the
front to pool moisture, decreasing confidence in fog development
further. Along and east of the Mississippi River where winds are
expected to be weakest and temperatures the coolest, at the very
least there is a low chance for steam fog.

An upper-level ridge will amplify over the Midwest on Sunday, with
low to mid-level flow becoming increasingly south-southwesterly
through the day. This flow will advect warm air into the region and
support 850 mb temperatures warming to 15-16 degrees C,
climatologically favoring afternoon temperatures topping out around
80 degrees beneath mostly clear skies.

Elmore

&&

.LONG TERM...  (Monday through Next Saturday)
Issued at 135 PM CDT Sat Oct 11 2025

Guidance consensus continues to depict an upper-level ridge sharply
amplifying over the Midwest on Monday. A weak cold front associated
with a surface low located well to the north in central Canada
will slowly ooze toward the CWA during the day on Monday. This
front will have minimal impact on our sensible weather mainly due
to deep southwesterly flow in its wake, preventing cold air
advection and supporting the front stalling and washing out
somewhere north of I-70. Meager moisture return ahead of the
front combined with the front`s weak forcing and rising heights
aloft will limit rain chances, with the probability for measurable
rainfall (0.01"+) topping out around 30% across northeastern
Missouri on Monday.

While guidance has begun to converge on a solution that supports the
axis of the upper-level ridge being located right over the Middle
Mississippi Valley or just to the west, the positioning of the
stalled front still varies to the point that temperatures for at
least the northern half of the CWA are uncertain through much of the
workweek. For areas south of I-70, NBM-based probabilities are
generally in the 50-70% range for high temperatures reaching 80
degrees through Thursday, while only 20-30% for areas north of I-70.

There is a strong consensus among guidance in the ridge breaking
down Friday into Saturday as a trough from the western CONUS phases
eastward. This would place the Middle Mississippi Valley beneath
deep southwesterly flow ahead of the trough, supporting warm air
advection. Probabilities of reaching or exceeding 80 degrees for
highs on Friday hit 70-90% on Friday, with probabilities falling
slightly on Saturday as some guidance has a cold front approaching
the CWA.

Elmore

&&

.AVIATION...  (For the 00z TAFs through 00z Sunday Evening)
Issued at 522 PM CDT Sat Oct 11 2025

Mainly dry and VFR conditions are expected through the period. The
only exception will be river fog late tonight (80-13Z) that will
likely affect SUS, JEF, and CPS with MVFR (possible IFR)
visibilities. Otherwise, light winds tonight will turn out of the
southeast by mid-morning Sunday at less than 10 knots.

Britt

&&

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

$$

WFO LSX