229
FXUS63 KLSX 061951
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
251 PM CDT Sat Sep 6 2025

.KEY MESSAGES...

- Temperatures will begin warming early next week, rising above normal
  by the middle to end of the week.

- Confidence in measurable rainfall remains low (10% or less)
  through next week.


&&

.SHORT TERM...  (Through Late Sunday Night)
Issued at 225 PM CDT Sat Sep 6 2025

Current water vapor imagery shows and expansive trough digging into
the eastern CONUS, with flow over the Middle Mississippi Valley
becoming increasingly northwesterly. This flow is spreading an
expansive area of high pressure at the surface across the Plains and
into the Midwest. A shortwave digging equatorward tonight into
tomorrow along the backside of the trough will aid in slowing its
exit from the region, keeping our weather consistent through Sunday.

Mostly clear skies allowing for ample sunshine are helping
temperatures rise into the mid 70s this afternoon, with similar
conditions forecast for Sunday. Tonight, temperatures will once
again drop into the mid 40s to around 50 for lows - similar to last
night. As we saw this morning, steam fog/valley fog is possible
again tonight due to these cool temperatures, though dew points are
forecast to be slightly lower. This leads to low confidence in
another round of fog, though we will continue to assess the need for
adding it to the forecast through the evening.

Elmore

&&

.LONG TERM...  (Monday through Next Saturday)
Issued at 225 PM CDT Sat Sep 6 2025

As we start the workweek, ensemble means support a gradual warm up
in temperatures compared to those over the weekend. This is due to
troughing weakening over the eastern CONUS, allowing for the surface
high to shift eastward and return some degree of southerly flow to
the region. Despite this subtle pattern change supporting warming,
ensemble means for temperatures (upper 70s) will be right at to just
below climatological normals on Monday.

Confidence is high in a more notable jump in temperatures Tuesday
and Wednesday, with warmer than normal conditions forecast into the
weekend. During the mid-week stretch, the upper-level trough will
continue to weaken and shift from the eastern CONUS as a ridge
amplifies over the Plains and into the Midwest. Low to mid-level
flow will become increasingly southerly to southwesterly, supporting
robust warm air advection over the Middle Mississippi Valley. By
Wednesday, guidance consensus is that 850 mb temperatures will have
warmed into the upper teens (degrees C), climatologically favoring
surface temperatures in the upper 80s to around 90 degrees through
the remainder of the week - nearly 10 degrees above seasonal
normals. Given the recent lack of rain, vegetation beginning to
seasonally transition to fall, and the main fetch from the Gulf
remaining over the Plains, boundary layer moisture is expected to
remain low through this stretch of warmth. This mitigates concerns
for high humidity and heat index values. The dry air will lead to
large diurnal swings in temperatures, with overnight lows falling to
around 60 degrees.

Elmore

&&

.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1153 AM CDT Sat Sep 6 2025

Confidence is high in dry and VFR flight conditions through the
TAF period at all local terminals. There is a low chance for
valley fog overnight that would most likely impact KJEF and KSUS
if it develops. However, confidence is low enough in this threat
that it has been left out of the TAF.

Elmore

&&

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

$$

WFO LSX