007
FXUS63 KLSX 160339
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1039 PM CDT Wed Oct 15 2025

.KEY MESSAGES...

- Above normal temperatures will continue through Friday. There
  may be some sprinkles across parts of the area this evening, but
  accumulating rainfall is not expected.

- Much-needed rainfall is still expected on Saturday ahead of a
  strong cold front. There is a conditional threat for severe
  storms Saturday, although confidence in severe weather remains
  low at this time.


&&

.SHORT TERM...  (Through Late Thursday Night)
Issued at 237 PM CDT Wed Oct 15 2025

The weather pattern continues to be dominated by a high amplitude
ridge over the central U.S. and long wave troughs to the west and
east.  The warm and (mostly) dry weather will therefore continue
through the short term.  The 850mb high which is currently centered
over central Missouri will drift into western Illinois by early this
evening.  Weak moisture convergence on the western side of the high
is producing some sprinkles across parts of central and northeast
Missouri, and there have been several reports of trace to 0.01 inch
of rain.  Short range guidance continues to show the potential for
very light precipitation into this evening due to this moisture
convergence. However forecast soundings have a very dry layer below
850mb so accumulating rainfall is very unlikely.  Will therefore
keep "sprinkles" in the forecast for this evening with PoPs below 15
percent.  The strongest moisture convergence moves into
west/northwest Illinois late tonight and Thursday, and with that the
chance for any further precipitation should end in the short
term. Temperatures will continue to be well above normal through
Thursday night with highs in the 80s and lows in the upper 50s to
low 60s.

Carney

&&

.LONG TERM...  (Friday through Next Wednesday)
Issued at 237 PM CDT Wed Oct 15 2025

The primary concern in the medium range is the potential for
severe thunderstorms on Saturday.  The upper level pattern continues
shifting east on Friday, which brings return flow to the Plains and
Mississippi Valley. The long wave trough over the western U.S. opens
up and lifts across the northern Plains, forcing low level
cyclogenesis which develops a cold front stretching from Minnesota
to northern Texas by early Friday evening.  The front stalls Friday
night as the mid-upper level wave continues northeast into Canada.
There should be plenty of time Friday and Friday night for southerly
flow to bring 60+ degree dew points back into the Mid Mississippi
Valley ahead of the front.  Meanwhile, another short wave trough
digs into the Plains Saturday and continues east into the
Mississippi Valley Saturday night.  This wave ultimately pushes the
cold front through Missouri and Illinois by early Sunday morning.
There continue to be timing differences between the deterministic
GFS and ECMWF with regards to the passage of the front through the
area.  There are also timing differences between the 00Z-06Z-12Z
runs of these models.  The latest runs are showing a slower eastward
progression of the front, and more instability with better surface
heating by early afternoon. However, the highest instability is
farther to the west and southwest than earlier runs.  Also, this
higher instability is somewhat questionable as the low level jet
will be producing moisture convergence in the warm sector, likely
resulting in clouds and showers which would limit heating.

All of this adds up to a great deal of uncertainty in the forecast
for Saturday.  Still think the most likely scenario on Saturday is
for widespread showers with scattered sub-severe thunderstorms
producing much-needed rainfall across the area, mainly in the
afternoon and evening. I would like to see more run-to-run
consistency, and agreement between models before getting too
concerned about severe thunderstorms, however the potential is
there, particularly since there will be 50+ kts of deep layer shear.
 Forecast soundings are not indicating particularly low LCLs, but
rotating storms would be possible given the shear, particularly if
the deterministic GFS`s MLCAPE of 1200+ J/Kg is realized.
Unfortunately, the uncertainty in the forecast may not improve until
the kicker short wave is sampled by the upper air network Friday
night.

The remainder of the medium range looks relatively quiet.
Temperatures cool to near or slightly below normal for Sunday behind
the front.  There are some indications that there will be lingering
showers on Sunday morning, although the latest model runs are now
completely dry.  Temperatures warm a few degrees above normal again
Monday and there may be another chance for rain Tuesday as another
fast-moving short wave moves through the Mississippi Valley, however
it looks like the moisture return ahead of the wave will be limited
since it will be progressing quickly through the region. The cold
front associated with Tuesday`s wave will bring another shot of
cooler air midweek.


Carney

&&

.AVIATION...  (For the 06z TAFs through 06z Thursday Night)
Issued at 1039 PM CDT Wed Oct 15 2025

VFR flight conditions and east-southeasterly winds are expected
to prevail at the local terminals through the TAF period.

Elmore

&&

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

$$

WFO LSX