Belleville, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

442
FXUS63 KLSX 201105
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
605 AM CDT Tue Oct 20 2026

.KEY MESSAGES...

- Dry and seasonably warm conditions will persist through the
  end of the week.

&&

.SHORT TERM /THROUGH WEDNESDAY/...
Issued at 227 AM CDT Tue Oct 20 2026

The forecast for the next several days can be summed up in one
phrase - status quo. With an omega block in place in the mid-levels
and high pressure stationed over the eastern CONUS at the surface,
there is no reason for our sensible weather to change. The small
increases in temperature we expect over the week can be attributed
to persistent insolation rather than any sort of advection or
dynamical reasoning. High clouds blowing into the region from the
southern Plains may enter Mid-Missouri slightly before peak heating,
which would prevent that area from gaining that degree or two of
warmth this afternoon - a negligible difference on human skin. In
all, the forecast today calls for highs around 70 degrees with very
little wind and plenty of sun. Add a degree and we have the forecast
for Wednesday as well. The high clouds and warmer afternoon will
support higher low temperatures tonight for our Missouri counties.
To the east where skies will be clearer for longer, radiational
cooling is expected to create similar conditions to this morning.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Issued at 227 AM CDT Tue Oct 20 2026

The forecast from Wednesday night through the end of the week is the
same as that of today and tomorrow. Widespread 70s increase a degree
or two each day unless warming is perturbed by high clouds. Late in
the week mid-level ridging will be shoved eastward and flattened as
a longwave trough strengthens over the Four Corners region. This
system is forecast to drive a cold front into the Midwest late
Saturday into Sunday, but latest model guidance indicates the front
will pivot into a more west-east orientation before it reaches
Missouri/central Illinois. This would keep accompanying rain and
cold air to our north and lengthen the duration of our warm streak.
Ensembles, aside from the GEFS, appear to support this solution. 850
mb temperatures Sunday into Monday are still forecast to be about
10C - the same as today - so a drastic cooldown within that period
is not likely if the models are correct. Beyond that guidance
diverges, and that`s reliant on if the cold front does push through
the CWA or not Monday into Tuesday. The NBM high temperature IQRs
reflect the uncertainty quite well, with KSTL jumping from a 4
degree split on Sunday to a 12 degree split by Tuesday.

&&

.AVIATION /12Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 604 AM CDT Tue Oct 20 2026

After the morning river and valley fog dissipates, dry and VFR
conditions with light winds will prevail through the remainder
of the period.

&&

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

&&

$$

SHORT TERM...Jaja
LONG TERM...Jaja
AVIATION...Jaja