Hidden Valley

000
FXUS63 KLSX 111142
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
642 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 /12Z TAFS THROUGH 18Z SATURDAY/...
Issued at 633 AM CDT Fri Sep 11 2026

Visibilities and ceilings have improved recently at all of the 
airports except UIN. Do expect improvement to MVFR at UIN by 15Z
and VFR at 18Z. Also expect current MVFR conditions at COU/JEF
to improve to VFR by 17Z. The lower LIFR ceilings at SUS should
improve by 13Z. Most of the terminals will have dry and VFR 
conditions this afternoon and this evening with scattered 
showers and thunderstorms staying over southeast Missouri and 
southwest Illinois. Additional fog will likely develop after 06Z
tonight with MVFR/possible IFR visibilities.

&&

.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...Britt