271
FXUS63 KLSX 291934
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
234 PM CDT Thu Oct 29 2026

.KEY MESSAGES...

- Above average temperatures will continue into early next
  week.

- Showers and a few thunderstorms are expected at times Friday
  through the weekend, mainly Friday morning and Saturday
  night/Sunday morning with plenty of dry time otherwise.

- Confidence is high in widespread, beneficial rainfall early to
  mid-next week.

&&

.SHORT TERM /THROUGH FRIDAY/...
Issued at 232 PM CDT Thu Oct 29 2026

Early this afternoon, a cold front is slowly advancing southward
into the I-70 corridor. Surface convergence, increasing instability,
and a weak capping inversion may be sufficient to overcome weak mid-
level height rises/subsidence and produce isolated showers, perhaps
a thunderstorm, in the next couple of hours through sunset. CAMs
disagree on whether or not development actually occurs, however,
with HREF probabilities of measurable rainfall only around 10 to 20
percent.

As a modest (20 to 25-kt) southwesterly LLJ develops overnight, a
more robust signal for showers and some thunderstorms exists late
tonight through Friday morning across northern MO into IA, including
portions of northeastern MO/west-central IL within low-level WAA
extending to the north of the stalling front. These showers and
thunderstorms may continue at times well into the day Friday as the
LLJ is slow to weaken and some additional development could occur
along the surface front as it lifts northward, but the strongest
forcing and greatest coverage is anticipated to gradually shift
northward through the day. There will be a spread in temperatures on
Friday with highs ranging from near 80 F in southeastern MO to the
60s F across northeastern MO/west-central IL north of the front and
within clouds and precipitation through the day. In between, exact
temperatures are uncertain due to sensitivity on how quickly the
front lifts northward.

&&

.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
Issued at 232 PM CDT Thu Oct 29 2026

Between Friday night and Sunday, a series of upper-level shortwave
troughs are progged to track northeastward through the Mid-
Mississippi River Valley. The first of which will pass Friday night
into Saturday, but only widespread clouds with isolated light
showers or sprinkles are anticipated, since forcing will be mainly
confined to mid-levels and there will be a deep dry layer below.
Therefore, conditions will be mainly dry on Saturday, through
evening Halloween festivities. With the second shortwave trough, low-
level forcing and moisture will be more favorable for showers late
Saturday night into into Sunday morning, supported by 30 to 60
percent probabilities of measurable rainfall in global ensemble
model guidance. These showers will be light, but probabilities of
0.25"+ are 30 to 40 percent across southeastern MO/southwestern IL,
suggesting showers could be more persistent and relatively "heavier"
in those areas. With considerable cloud cover both Saturday and
Sunday, high temperatures will be limited to the upper 60 to low-70s
F and with a small diurnal range including low temperatures in the
50s to around 60 F. These temperatures are still above average for
the end of October/beginning of November.

Global model guidance continues to be in agreement that a more
potent upper-level trough will slowly propagate across the central
CONUS from Monday through mid to late next week. There is
considerable variability across model guidance solutions on the
structure and speed of the trough since it will likely be composed
of multiple shorter wavelength troughs interacting and phasing (or
not phasing) with one another. Although these details are uncertain,
an anomalous (>90th climatological percentile), deep meridional
component to the flow with anomalous PW around the 97.5 to 99th
climatological percentile and slow system motion all provide strong
support for a widespread rainfall event across the region. NBM
probabilities of 1"+ in 48 hours are 40 to 70 percent across the
CWA, highest in central and northeastern MO. However, there is
spread on the timing and duration of this rainfall which will impact
amounts. Temperatures are also uncertain with the NBM interquartile
reaching around 10 F by late next week, but an underlying cooling
trend increases confidence that clouds and precipitation, then
eventual CAA with this system will inevitably cool temperatures
closer to average.

&&

.AVIATION /18Z TAFS THROUGH 00Z SATURDAY/...
Issued at 1227 PM CDT Thu Oct 29 2026

A few isolated showers, perhaps a thunderstorm, are possible (20
percent chance) late this afternoon and evening near I-70, but there
is very low confidence in impacts. Additional showers and a few
thunderstorms are expected early Friday morning, continuing well
into the day across northeastern MO and west-central IL; however,
only a PROB30 group has been included at KUIN for now with some
uncertainty in their exact location. Otherwise, dry and VFR flight
conditions will persist with light winds becoming variable or
northerly behind a stalling front, then easterly on Friday.

&&

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

&&

$$

SHORT TERM...Pfahler
LONG TERM...Pfahler
AVIATION...Pfahler