385
FXUS63 KLSX 290310
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1010 PM CDT Thu Aug 28 2025

.KEY MESSAGES...

- There may be an isolated shower or two on Friday afternoon in
  the vicinity of a back door cold front moving through the area.
  The chance for rain is less than 20 percent.

- Temperatures will remain seasonably warm to a few degrees below
  normal with dry weather expected through the weekend.


&&

.SHORT TERM...  (Through Late Friday Night)
Issued at 250 PM CDT Thu Aug 28 2025

The pattern aloft is becoming more amplified this afternoon.  A
short wave trough is digging through the Ohio Valley into the base
of the long wave.  This will drag the surface high currently
centered over Canada`s Ontario Province south into the Upper Midwest
and Great Lakes Region tonight into Friday.  The leading edge of
this high will be a back door cold front that is expected to drift
from southern Wisconsin south-southwest through much of Illinois
tonight.  The cool dry airmass which moved into our region a few
days ago has modified enough over to provide a small amount of
instability in the vicinity of the front Friday afternoon.  A few
CAMs develop isolated convection across eastern Missouri and western
Illinois. The showers are few and far between, and most
deterministic guidance shows no precip at all.  Have therefore kept
PoPs below mentionable levels Friday afternoon for this forecast.
Temperatures tonight and Friday should be nearly a carbon copy of
today`s with lows Friday morning mainly in the 50s, except low 60s
in St. Louis, and highs in the low to mid 80s.

Carney

&&

.LONG TERM...  (Saturday through Next Thursday)
Issued at 250 PM CDT Thu Aug 28 2025

The upper level pattern shifts east and attenuates somewhat late
in the weekend and early next week.  However this minor pattern
shift is short lived as a short wave trough will move across the
Midwest Monday into Tuesday.  The deterministic GFS and ECMWF are
now printing out precip across a good portion of Missouri and
mostly southern Illinois during this time frame.  However the LREF
cluster analysis is showing some variance in the position and
amplitude of the trough and a majority of the members (70-80%)
remain dry through late Tuesday.  The percentage of LREF members
that forecast precipitation increases to around 50% on Wednesday as
another cold front is pushed through the area, driven by the short
wave phasing into and amplifying long wave pattern.  The NBM
appropriately increases PoPs from no chance/slight chance Monday and
Tuesday, up to around 30% on Wednesday as the front moves through.
Temperatures through Wednesday will be seasonably warm in the low to
mid 80s, to a few degrees below normal in the mid to upper 70s.
The LREF is showing a considerable amount of variance with the
amplitude of the long wave trough on Thursday, but the position of
the trough over the Great Lakes and western Ohio Valley looks more
certain.  Cooler weather is expected on Thursday behind the front,
however the uncertainty with respect to the depth of the trough
translates into uncertainty in the temperature forecast.
Interquartile range of high temperatures is as wide as 10 degrees on
Thursday ranging from the mid 60s to mid 70s.

Carney

&&

.AVIATION...  (For the 06z TAFs through 06z Friday Night)
Issued at 1008 PM CDT Thu Aug 28 2025

VFR conditions are expected throughout the 06Z TAF period. Light
and variable winds will become primarily east-northeasterly
tomorrow afternoon and continue through the end of the period, but
will remain light. A low chance of patchy steam fog development
exists along main stem rivers overnight and early tomorrow
morning, but this is not likely to impact nearby terminals
(SUS/JEF/CPS).

BRC

&&

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

$$

WFO LSX