972
FXUS63 KLSX 291136
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
636 AM CDT Wed Jul 29 2026

.KEY MESSAGES...

- Temperatures will be near to slightly below normal today and
  Thursday. It will also be less humid than in recent days.

- Showers and a few thunderstorms are likely Thursday night
  through Friday night. A chance for rain lingers Saturday into
  Sunday.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 340 AM CDT Wed Jul 29 2026

A broad surface high will build south from Canada and the Upper
Midwest into the Mid Mississippi Valley today through Thursday.
Cooler and noticeably drier air will continue filtering into the
region as the high drifts into Illinois.  Guidance is showing dew
point temperatures falling into the mid 60s across most of the area
this afternoon, and this agrees well with current upstream
observations.  Forecast soundings show deep mixing to 900-850mb this
afternoon, where temperatures are between 18-20C along and west of
the Mississippi, and closer to 16-17C in central Illinois This mixes
down 88-91F at the surface across most of the area, with mid 80s
farther east.  These mix-down temps match up nicely with NBM and
traditional MOS highs today.  The lower dew point temperatures, a
mostly clear sky and light wind tonight will produce good
radiational cooling conditions to allow temperatures to drop into
the 60s in most locations.  Conditions on Thursday will be very
similar to today as the surface high drifts from Illinois into
Indiana, so NBM and MOS high temperatures ranging from the mid 80s
to around 90 look very reasonable.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Issued at 340 AM CDT Wed Jul 29 2026

The next upstream short wave moves into the Upper Midwest Thursday
night, and then southeast into Iowa and northern Illinois on Friday.
This morning`s model runs aren`t in as good agreement with the
strength and speed of the wave as it moves across the Midwest into
the Ohio Valley, and this translates into position, speed, and
strength differences with the low level reflection of the wave.
However, the model consensus supports increasing PoPs late Thursday
night into Friday morning, and then continuing precip chances
through Saturday.  The GFS and ECMWF both show enough instability
for thunderstorms Friday ahead of the surface low, with up to 30-
35kts of shear.  Could therefore see some organized convection
Friday with a damaging wind threat if there`s enough instability.
However that`s currently questionable as convective debris and
ongoing precipitation will probably limit daytime heating.  Mean
precipitable water values will be around 2 inches over our area on
Friday according to the latest run of the LREF. This is around the
95th percentile of climatology, so some locally heavy rain will be
possible, though the storms look like they should be progressive.

Models continue to print out light QPF Friday night and Saturday as
the short wave moves across the area and low level moisture wraps
back around the system.  Differences in the speed of the short wave
continue, and therefore timing the end of the precip chances is
uncertain. Many of the the time-lagged ECMWF ensemble members in the
latest LREF hang on to precip Saturday night into Sunday due to the
EC`s slower solution.  Some solutions even hang on to precip chances
Monday and Tuesday afternoon across southeast Missouri into southern
Illinois as the short wave lingers over the lower Ohio/Tennessee
Valley.  However the GEFS and GEPS members mostly dry us out by
Saturday evening.  Confidence in the precip forecast is low beyond
Saturday with all this in mind.  Temperatures through the period
will remain near to a few degrees below normal.  The coolest day
will likely be Saturday with clouds and showers with the surface
low east of the area over eastern Illinois or northern Kentucky.

&&

.AVIATION /12Z TAFS THROUGH 18Z THURSDAY/...
Issued at 629 AM CDT Wed Jul 29 2026

VFR flight conditions are expected to prevail through the
period. There are a few patches of MVFR and IFR ceilings mostly
confined to northeast and central Missouri. Satellite imagery
and surface observations are showing that these low clouds are
transient and don`t last very long at any one location. The
low clouds should lift and dissipate after sunrise.

&&

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

&&

$$

SHORT TERM...Carney
LONG TERM...Carney
AVIATION...Carney