952
FXUS63 KLSX 101947 CCA
AFDLSX

Area Forecast Discussion...CORRECTED
National Weather Service St Louis MO
247 PM CDT Thu Sep 10 2026

.KEY MESSAGES...

- Fog is expected in places overnight, particularly in
  central/northeast Missouri. Visibilites of 1 mile or less may be
  observed.

- Slowly increasing temperatures are expected tomorrow through
  early next week, reaching seasonable, but slightly above
  average values.

- Occasional chances (20-30%) for showers exist this weekend through
  early next week, but largely dry conditions are expected
  until Tuesday onward.

&&

.SHORT TERM /THROUGH FRIDAY/...
Issued at 214 PM CDT Thu Sep 10 2026

While widespread rain has largely ended across the region, the main
focus of the next couple of days will be the lingering potential for
a few afternoon showers, both today and tomorrow, as a weak cold
front stalls along our southern fringes. Fog is also expected to
develop in many areas overnight, perhaps becoming dense at times,
although confidence in the distribution of fog vs low clouds is
relatively low.

A narrow corridor of light showers remnant of this morning`s rain
has been slowly moving east throughout the day today, producing only
very light amounts that may not even be enough to wet the ground in
most places. However, widespread cloud cover HAS persisted, and
while humidity remains high, this cloud cover has significantly
limited afternoon heating and prevented the buildup of substantial
instability north of I-44. Across the Ozarks and further south,
though, more sun has allowed for the generation of between 250 and
500 J/kg of ML CAPE, with even some modest effective bulk shear in
place as well (35-45kt). As the afternoon wears on, the
aforementioned cold front will continue to slowly move southeast,
and convective initiation is likely by the time we reach peak
heating (3-5pm). Most of this is expected to occur just to our
southeast, but may briefly skirt our forecast area before quickly
exiting. These storms may eventually become strong or even severe,
but this is much more likely after they have moved out of the area.
Further north, a few weaker showers may also develop behind the cold
front, but much weaker instability should prevent these from
becoming particularly threatening.

Overnight, light winds, slowly clearing skies, and lingering
humidity/surface moisture should allow for the development of fog
and low clouds, with best chances for the former across
northeast/central MO and west-central IL where skies clear earlier.
As you progress further south, low clouds become more likely to
occur than fog, but exactly where this transition occurs is
uncertain. Some dense (<1/4 mile) fog is also well within reason,
but we will refrain from issuing any Dense Fog headlines until we
have higher confidence in the coverage of fog vs stratus. For
tomorrow, the previously mentioned cold front is expected to wash
out, and surface winds will gradually turn back to the southeast.
This should allow for a very modest warmup, and will also maintain
relatively high humidity levels throughout the area. As such, it
would not be a surprise to see a few showers in the afternoon,
particularly along/south of I-44 in closer proximity to a weak upper
level trough stalled across the lower Mississippi River Valley.
Aside from a brief heavy downpour and a stray strike of lightning or
two, this activity is not expected to be strong or severe.

&&

.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
Issued at 214 PM CDT Thu Sep 10 2026

Confidence in the day-to-day specifics remains relatively low from
Saturday onward, although we do expect temperatures to climb back to
slightly above average through early next week (for the most part),
followed by a cooling trend toward mid-week. Precipitation chances
are also rather nebulous during this timeframe, with sporadic
opportunities for showers between Saturday and Monday, followed by
expanding probabilities Tuesday onward as a cold front approaches.

Saturday through Monday, zonal to slightly northwesterly upper level
flow will persist, with a weakness in the upper ridge lingering just
to our southeast. Humidity will persist locally, but very few
local forcing mechanisms are depicted in model guidance. Further
west across the central plains, though, it does appear that a
persistent low-level jet will drive the development of one or
more convective, with relatively low confidence in their exact
placement and trajectory. While the focus of this activity is
expected to remain to our west, remnants of these storms may
graze our far western areas at times, and the lingering humidity
may be enough for us to see a few locally developing showers at
times, too. Again, timing and placement is very uncertain, but
areas of central/western MO are favored with the highest
precipitation probabilities (~30%). Much more dry time is
expected overall, though, and we don`t see substantial
opportunity for strong/severe storms locally. Meanwhile, above
average temperatures are favored, along with high humidity, but
not likely enough of either to produce headline-worthy heat
index values on a large scale. A weak cold front also adds an
element of uncertainty to the temperature forecast Monday,
particularly north of I-70.

From Tuesday onward, there are indications that a stronger shortwave
will begin to suppress the upper ridge across the central CONUS,
although variance among ensembles and ensemble clusters remains very
high. Both the timing and strength of this trough are very
uncertain, with differences of as much as 24 hours evident among
clusters, along with significant differences in strength. As such,
the timing of a cold front and its resulting impacts also remains
uncertain, although a cooling trend does appear likely over the
latter half of the week. Given the above, temperature spreads remain
high throughout this period, with 10-15 degree interquartile ranges
Tuesday onward, albeit with a slow downward trend. Meanwhile,
precipitation chances also gradually increase during this period,
but again with very high variance among ensemble members. In short,
slowly cooling temperatures are most likely Tuesday onward, with
increasing chances for showers and thunderstorms overall.

&&

.AVIATION /12Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1125 AM CDT Thu Sep 10 2026

Lingering showers and low ceilings are expected to gradually
diminish by the start of the 18Z period or very shortly
afterward. VFR ceilings should then prevail until evening,
although mid and high level cloud cover will be slow to clear
out completely. Overnight, the main concern is the potential for
low ceilings and fog, and confidence is low regarding the
relative coverage of each. Fog is most likely in
northern/western areas where mid/high clouds are less prevalent,
including at UIN/COU/JEF. IFR and even LIFR visibilities will
be possible wherever fog develops, but this will be less common
where low stratus cover develops instead. Where the latter
occurs, it will be low ceilings that impact flight categories
rather than visibilities, with MVFR ceilings at a minimum, and
the potential to drop lower at times. Ceilings should gradually
lift and scatter by the end of the period.

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

&&

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

&&

$$

SHORT TERM...BRC
LONG TERM...BRC
AVIATION...BRC