Cahokia Illinois Weather Forecast Discussion

203
FXUS63 KLSX 110322
AFDLSX
Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1022 PM CDT Fri Oct 10 2025
.KEY MESSAGES...
- Mostly dry conditions are expected to prevail through the forecast
  period.
- Above normal temperatures are forecast through Monday, with the
  temperature forecast next week being uncertain for most
  locations. Despite this, confidence is high that temperatures
  will at least be normal to above normal for this time of year.
&&
.SHORT TERM...  (Through Late Saturday Night)
Issued at 217 PM CDT Fri Oct 10 2025
Water vapor imagery this afternoon shows northwesterly flow over the
Middle Mississippi Valley, with a shortwave departing the region and
moving into the Ohio Valley. This shortwave was responsible for our
earlier rainfall, which has since dried up thanks to weakening
instability and a dry airmass over the CWA. Surface observations
show that a weak cold front extends from Wisconsin southwestward
through Iowa, northwestern Missouri, and into Kansas. This front
will push into the CWA via the northwesterly flow, but weaken as it
does so. Therefore, while isolated sprinkles can`t be ruled out,
additional impactful rainfall is not expected through this evening,
and only a minimal impact on temperatures is expected tonight and
tomorrow.
In fact, temperatures tonight are forecast to be warmer than last
night thanks to cloud cover limiting radiational cooling. However,
thanks to the recent rainfall, fog is now expected mainly across
portions of central and northeastern Missouri. This fog threat may
be enhanced by weak moisture convergence along the dissipating front
as it moves into the region.
As an expansive area of high pressure at the surface moves through
the Great Lakes tomorrow and skirts northern portions of the CWA,
temperatures will vary notably from north to south. Values will top
out in the low to mid 70s beneath increasingly clear skies for
locations north of the I-70 corridor, with upper 70s forecast along
and south of the corridor.
Elmore
&&
.LONG TERM...  (Sunday through Next Friday)
Issued at 217 PM CDT Fri Oct 10 2025
On Sunday, both ensemble clusters and deterministic guidance depict
a highly amplified ridge stretching from the Southern Plains
northeastward into the Great Lakes. Low to mid-level winds will
become increasingly south-southwesterly through the day, increasing
warm air advection over the Middle Mississippi Valley and pushing
afternoon temperatures into the low 80s for most locations across
the CWA - approximately 10-15 degrees above seasonal normals.
A weak cold front will drop toward the CWA on Monday, and similar to
the one on Friday, will undergo frontolysis as it enters the area.
Ensemble-based probabilities for measurable rainfall (0.01) top out
around 40% across far northeastern Missouri. Unfortunately for our
drought-stricken region, confidence in this solution is high, as the
upper-level ridge will be amplifying, heights rising across the
Middle Mississippi Valley, and moisture return ahead of the front
will be meager.
How far the post-frontal airmass makes it into the region for the
rest of the workweek varies among guidance due to differences in the
phasing of the ridge from Monday onward. For areas that are impacted
by the airmass, high temperatures are expected to be closer to
climatological normals (upper 60s to around 70 degrees), and if this
does occur, will most likely do so north of I-70. If the upper-level
ridge builds further into the region, then the airmass will struggle
to make inroads, leading to above normal temperatures persisting
across the entire CWA. If the ridge retrogrades westward, placing
the Middle Mississippi Valley beneath persistent northwesterly flow,
then seasonable temperatures are most likely through the week.
Guidance is approximately evenly split between these two solutions,
with the current forecast representing the middle ground.
Elmore
&&
.AVIATION...  (For the 06z TAFs through 06z Saturday Night)
Issued at 1019 PM CDT Fri Oct 10 2025
Fog development remains the primary concern overnight. Stratus is
slowly moving out from northwest to southeast, with KUIN having
cleared out within the past hour. Central Missouri sites should
see more clearing by 0600-0700 UTC, with fog developing shortly
thereafter. IFR visibilities are expected at all 3 terminals, with
a period of dense fog possible. The fog should lift Saturday
morning, with VFR conditions areawide for Saturday
afternoon/evening.
Further east, the stratus has begun to break up a bit. Didn`t add
any fog to the metro sites, but KSUS followed by KCPS would be the
main worries. Given the lack of rain (unlike further west) and
more cloud uncertainty, still left any fog mention out for now.
Gosselin
&&
.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&
$$
WFO LSX

NWS LSX Office Area Forecast Discussion