396
FXUS63 KLSX 110836
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
336 AM CDT Fri Sep 11 2026

.KEY MESSAGES...

- Areas of dense fog is expected through mid-morning, especially across
  central and northeast Missouri into west central Illinois
  where a Dense Fog Advisory is in effect.

- There are chances (20-30%) for showers and a few thunderstorms through
  this weekend with better chances next week. Isolated storms
  late Saturday night could produce gusty winds and heavy
  downpours over central and northeast Missouri.

- Slowly increasing temperatures are expected through early next
  week.

&&

.SHORT TERM /THROUGH SATURDAY/...
Issued at 335 AM CDT Fri Sep 11 2026

The latest satellite imagery is showing fog persisting across parts
of central and northeast Missouri into west central Illinois early
this morning.  Surface observations are showing multiple
observations at 1/4 mile where we already have a Dense Fog Advisory
in effect until 10 am.  Fog continues to develop southeast of the
advisory area where there is thinning in the clouds, with a few
locations reporting dense fog in the river valleys.  Will continue
to monitor for an expansion of the advisory the next few hours if we
continue to get more reports.  This fog will eventually dissipate
when we begin to see some low level mixing later this morning.

The latest run of the RAP is showing a weak upper low moving slowly
northeast across the area today and tonight.  Forecast soundings are
showing weak positive areas, with the only uncapped sounding at FAM.
 Will keep with a 20-50% chance for showers and thunderstorms today
mainly across the southern CWA and continuing into the southeastern
CWA tonight.  With light winds and moist conditions in the boundary
layer, the HREF probabilities and MOS guidance is pointing for
additional fog late tonight over central and southeast Missouri and
in river valleys.

I expect more sun today than yesterday, so highs should climb back
into the lower to mid 80s.  With 850mb temperatures climbing back to
around 20C on Saturday, highs are forecast to be in the upper 80s in
most areas.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Issued at 335 AM CDT Fri Sep 11 2026

Thunderstorms are expected to develop over western Missouri on
Saturday afternoon and evening and move eastward Saturday night.
There continues to be spread in the models on where these
thunderstorms track, with the NAM showing a more robust complex of
storms that moves to the southeast that would affect central
Missouri versus the GFS that has less QPF that moves to the east. We
will continue with just a 20-30% chance of showers and thunderstorms
after midnight on Saturday night.  There remains some possibility
per the latest SWODY2 that one or two of these storms will be
capable of producing damaging winds along with locally heavy
rainfall per WPC.

The chance for showers and thunderstorms will be mainly confined
across northeast Missouri and west central Illinois Sunday into
Monday in close proximity to a front as a large upper high builds
over the southern CONUS.  The front will move southeast by Tuesday
and become stalled over the area through Thursday with the LREF
having 40-60% of its members producing rain at St. Louis during this
timeframe.

With a front in the area, there will be a contrast in highs with 80s
over the north and 90s in the south.

&&

.AVIATION /06Z TAFS THROUGH 12Z SATURDAY/...
Issued at 200 AM CDT Fri Sep 11 2026

Dense fog will result in IFR/LIFR flight conditions at northern
terminals through mid morning, improving between 14-16Z. MVFR
ceilings may linger around the St. Louis metro through midday,
but then partway to VFR conditions with light winds.

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Dense Fog Advisory until 10 AM CDT this morning for MOZ018-019-
     026-027-034>036-042.
IL...Dense Fog Advisory until 10 AM CDT this morning for ILZ095>097.

&&

$$

SHORT TERM...Britt
LONG TERM...Britt
AVIATION...WFO ILX