688
FXUS63 KLSX 032333
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
633 PM CDT Wed Sep 3 2025

.KEY MESSAGES...

- Showers and a few thunderstorms are expected along and behind a
  cold front tonight. The chance for rain remains 50-70 percent
  for most of the area.

- Temperatures will be cooler than normal for the rest of the week
  into the weekend. The coldest day is expected to be Friday with
  clouds and more showers behind another cold front.


&&

.SHORT TERM...  (Through Late Tonight)
Issued at 242 PM CDT Wed Sep 3 2025

A cold front currently extending from northwest Missouri into
southeast Iowa will move through our forecast area from late this
afternoon through this evening.  All model guidance develops precip
along and behind the front to a greater or lesser degree between 21-
00Z.  Most CAMs show scattered convection moving southeast through
the evening with only 40-50% coverage, however there are a few that
show more conglomeration of the showers which would provide a more
widespread rain.  Still think a 50-70 PoP is appropriate tonight as
the front moves through.  The RAP, and to a much lesser extent the
GFS show some elevated instability in the vicinity of the front this
evening, so a few rumbles of thunder are likely.  However, the
instability is fairly weak (<1000 J/Kg) and the best shear lags
behind it, so severe storms should stay out of our forecast area
this evening.

Carney

&&

.LONG TERM...  (Thursday through Next Wednesday)
Issued at 242 PM CDT Wed Sep 3 2025

Stacked low pressure centered between Lake Superior and The Hudson
Bay will be the dominant weather feature over the eastern half of
North America for the remainder of the week and at least the first
part of the weekend.  The long wave trough associated with the low
will extend south through the Great Lakes Region all the way to The
Gulf Coast, moving little through the period. The LREF is showing 4
clusters that all look remarkably similar with the position of the
low.  Variability appears to be with the depth of the low as
indicated in the EOF patterns, although the spread in the 500mb
heights is 50 meters or less through Friday night/Saturday morning.
At the surface, high pressure will build across the Mid Mississippi
Valley behind tongight`s cold front.  Temperatures on Thursday will
be noticeably cooler, mainly in the mid 70s.  The high moves east
pretty quickly ahead of a short wave spinning into the Upper Midwest
around the upper low Thursday night.  This wave will drive another
cold front through Missouri and Illinois on Friday, with another
chance for rain, primarily post-frontal late Friday afternoon into
Friday night.  A sprawling surface high builds across the Midwest,
Great Lakes, and Ohio Valley and remains locked in place at least
into early next week due to the blocky pattern.  The LREF mean 500mb
forecast does start shifting that pattern late Monday into Tuesday,
bringing an upper level ridge into the Plains, though the cluster
analysis shows much less agreement on the strength and position of
the ridge than it did earlier in the period with respect to the
upper low.  Below normal temperatures, mainly in the mid 70s are
expected through Monday.  Friday`s temperatures may not get out of
the upper 60s along and north of I-70 immediately behind the cold
front due to clouds and (hopefully) rain. Tuesdays`s temperatures
will be close to if not a bit above normal if the upper ridge ends
up moving into the Plains as the ensembles suggest.

Carney

&&

.AVIATION...  (For the 00z TAFs through 00z Thursday Evening)
Issued at 626 PM CDT Wed Sep 3 2025

A cold front will continue to press southeast tonight, shifting
winds to northwesterly as it passes. A few thunderstorms have
developed along the front. These will continue to weaken this
evening as we lose heating, but may cause a rumble of thunder and
possibly MVFR cigs and vsbys at KSTL/KSUS/KCPS early in the TAF
period depending on how they hold up. Light showers and MVFR to
IFR cigs will follow the front into the early morning hours.
Though light showers are possible for areas generally along and
south of I-70, MVFR to IFR cigs will be mainly confined to the
eastern Ozarks. These will dissipate shortly after sunrise. Winds
will then shift to southerly/southwesterly late in the period.

Jaja

&&

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

$$

WFO LSX