288
FXUS63 KLSX 250700
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
200 AM CDT Sun Oct 25 2026

.KEY MESSAGES...

- Warm days and crisp fall nights continue through the end of
  the coming workweek.

- Rain chances return for Halloween weekend.

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 200 AM CDT Sun Oct 25 2026

A persistent blocking pattern remains in place across North America
and has led to our stagnant weather pattern for the last week or so.
A trough over the East Coast and western Atlantic extends all the
way south to Cuba. Another trough over the West Coast extends down
to Baja California. In between, a high amplitude ridge extends from
Texas to Hudson Bay. Highly amplified patterns like this tend to
stick around for a while before finally breaking down. Our area is
solidly under the influence of the ridge with broad surface high
pressure stretching from Quebec to the Deep South. This surface high
has kept Gulf moisture blocked well to the south, only making a
northward push through west Texas and the High Plains.

The result for us locally will continue to be warm days and cool
crisp nights. With daytime heating we mix into the warmth within the
ridge with temperatures reaching the 70s to near 80. But the dry
air, calm winds, and longer fall nights allow for nocturnal cooling
into the upper 40s to near 50. The only recent addition to this
pattern has been some increased high level cloud cover as the ridge
axis has shifted a bit further east and high level moisture streams
over the top of it. These clouds will have some minor effect by
decreasing the extreme diurnal temperature ranges. Areas that get a
little less sun will have a tougher time reaching 80 degrees despite
the warm ridge. But that same blanket of clouds will dampen the
nighttime cooling as well, with fewer locations dropping into the
40s.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Issued at 200 AM CDT Sun Oct 25 2026

By in large the stagnant pattern continues for us locally through
the upcoming week, though there will be some movement to cut back on
the extreme blocking. Just as there`s some easing in the eastern
trough, portions of the western trough eject northeast around the
ridge, cutting back on its intensity and amplitude. The most
significant is on Monday when the core of the western US trough
exits through Colorado into Minnesota by Tuesday. Guidance is in
good agreement that this passes far enough to our north to avoid any
significant impacts locally aside from increased mid and high level
cloud cover. There is a cold front behind this trough, but it gets
hung up over Iowa Wednesday into Thursday keeping us warm and dry
south of it.

There is some restructuring of the pattern from a high amplitude
ridge to a broader, flat topped ridge over much of the central and
eastern US with the jet near the Canadian border. Out west, although
one trough ejects, it`s soon replaced by a new one dropping south
out of Alaska into the Northwest US. While this general idea is
agreed upon, guidance varies wildly in how this next trough
progresses late this week and into the following week. Locally,
though, we transition to more of a southwesterly upper level flow
with better moisture transport through our region. While the precise
details vary, this does translate to increased rain chances
eventually, just in time for the Halloween weekend. These chances
peak Saturday into Sunday when at least one shortwave trough is
expected to pass near the region. Among the 00Z ensemble guidance,
80 to 90 percent of members produce measurable rain across our
entire forecast area in the 24 hours ending at noon on Sunday. This
indicates strong confidence that at least some rain will fall
locally this weekend. Latest NBM PoP peaks at only 60 percent due
primarily to timing uncertainty (will it fall Saturday, Saturday
night, or Sunday?).

Looking beyond this weekend, there`s a general consensus that the
ridge fully breaks down and some flavor of troughing arrives early
next week. But whether this represents a return to more "normal"
temperatures or something even cooler is not well agreed upon.

&&

.AVIATION /18Z TAFS THROUGH 00Z MONDAY/...
Issued at 554 PM CDT Sat Oct 24 2026

Dry and mainly VFR conditions are expected to continue through
the period. The potential for river fog recurring at SUS or CPS
remains too low to include in this issuance of the TAFs.
Otherwise winds will remain below 10 knots.

&&

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

&&

$$

SHORT TERM...Kimble
LONG TERM...Kimble
AVIATION...Britt