571
FXUS63 KLSX 251935
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
235 PM CDT Sun Oct 25 2026

.KEY MESSAGES...

- Seasonably warm and predominantly dry conditions will
  continue through the work week.

- There is a 60 to 80 percent chance of rain next (Halloween)
  weekend, although timing is not certain.

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 234 PM CDT Sun Oct 25 2026

An Omega Block spanning the CONUS will keep an upper-level ridge
locked in place over the Mid-Mississippi River Valley through late
Monday. As a result, there will be little/no change in airmass, but
increasing/thickening upper-level clouds will result in slightly
warmer low temperatures tonight and high temperatures a degree or
two cooler on Monday, although still firmly in the 70s F.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Issued at 234 PM CDT Sun Oct 25 2026

An upper-level trough ejecting northeastward across the Central
Plains to Upper Midwest will result in a weakening of the Omega
Block and a slight eastward displacement of the upper-level ridge
around Tuesday into Wednesday. The glancing passage of the trough
will at least provide increasing clouds, but it is unlikely to be
sufficient for any precipitation with limited moisture return.
However, the pattern will subsequently become more favorable for
moisture return, which, when combined with a wavering front reaching
as far southeastward as northern/northeastern MO during the second
half of the week, leads to increasing ensemble membership with
measurable rainfall in that portion of the CWA. This rainfall would
be in the form of a few showers at times, with the vast majority of
the period still expected to be dry while low-level southwesterly
flow south of the front maintains seasonably warm conditions.
Thursday is forecast to be the warmest day of the forecast period as
the ridge briefly amplifies again, accompanied by high temperatures
in the 80s F for parts of the CWA.

As the ridge weakens again next weekend with another upper-level
trough passage and more time for moisture to increase, there is a
stronger signal for rainfall across the CWA. Around 70 to 90 percent
of global ensemble model membership has measurable rainfall at some
point next weekend with 40 to 50 percent probabilities of greater
than 0.25". However, PoPs in the current forecast are slightly lower
due to them being 6 hourly with timing uncertainty. There is little
support for this trough to have a front that provides much, if any,
airmass change, but clouds and precipitation have the potential to
temporarily cool temperatures. For context, although the NBM
interquartile temperature range does increase to around 8 F next
weekend, even the 25th percentile is still above average for the end
of October/beginning of November.

&&

.AVIATION /18Z TAFS THROUGH 00Z TUESDAY/...
Issued at 1214 PM CDT Sun Oct 25 2026

Dry and VFR are forecast to continue through the TAF period. Patchy
river valley fog cannot be ruled out Monday morning, but coverage
should be less than previous mornings and confidence is lower in any
TAF site impacts. Winds will remain light, becoming more
southwesterly during the day Monday.

&&

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

&&

$$

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