058
FXUS63 KLSX 091922
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
222 PM CDT Tue Sep 9 2025

.KEY MESSAGES...

- Well-above normal temperatures and mostly dry weather is
  expected though this weekend and potentially into early next
  week.


&&

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 221 PM CDT Tue Sep 9 2025

The transition out of fall like temperatures is underway this
afternoon as readings have climbed into the upper 70s to near 80
degrees. These values are still a bit cooler than normal for the
date, but about 5-6 degrees warmer in most locations than 24 hours
ago. Milder conditions are forecast for tonight, with weak
southerly surface winds and SCT-BKN midlevel cloudiness. Lows are
only expected to drop back into the mid 50s to low 60s. I cannot
rule out a few sprinkles overnight, but the better midlevel
forcing associated with a remnant MCV should be moving east of the
area. There is some weak low-level moisture convergence, but dry
low levels/high cloud bases suggests anything other than sprinkles
reaching the ground is unlikely. Therefore, kept any mentionable
PoPs out of the forecast.

Summer returns on Wednesday with plenty of sunshine and well-above
normal temperatures. The combination of plentiful solar insolation,
low-level warm air advection, and deep mixing (~800 hPa) will help
yield highs in the mid to upper 80s. These values would be about 5
degrees above normal for the date and the warmest temperatures for
most locations in ~2 weeks.


Gosselin

&&

.LONG TERM...  (Wednesday Night through Next Tuesday)
Issued at 221 PM CDT Tue Sep 9 2025

The summerlike pattern will continue through at least this weekend
with building mid/upper level ridging overhead and 850-hPa
temperatures climbing closer to +20C (>95th percentile of
climatology). Anomalously warm temperatures (especially during the
day) will also be aided by the ongoing dryness/drought and
associated dry soils. The hottest days are most likely to be on
Saturday/Sunday as this is when the ridge is directly overhead and
850-hPa temperatures peak. Highs in the mid 90s are expected, but a
few spots get into the upper 90s if it can stay sunny long enough.
Cloud cover is the only potential limiting factor, and soundings do
show a return to diurnal cumulus starting on Thursday. The signal
for more SCT-BKN cumulus gets stronger with each passing day as
well. This should help put a "cap" on highs and keep them from
flirting with more widespread upper 90s to near the century mark.

In terms of precipitation chances, mostly dry weather is expected
through Saturday night. By Sunday, there is at least a low chance
that a mid/upper level trough moves into the Great Lakes and helps
bring a backdoor cold front into the region. The trend however has
been a bit toward a weaker/further east track of this trough over
the past 24 hours. Clusters of the 500-hPa height pattern only show
about a third of members from the grand ensemble with this scenario.
In addition, nearly all of those are EPS members. Generally, when 1
of the 3 suites is different, that solution tends to trend more
toward the other 2 (GEFS/GEPS in this instance) over time. One
caveat to the mostly dry forecast is the possibility of diurnal
showers and thunderstorms. The pattern is very reminiscent of mid
Augusts, which featured very warm temperatures but also several days
of isolated-widely scattered showers and thunderstorms each
afternoon. The 700-hPa temperatures do not appear to be too warm
(generally below +10C), suggesting not too strong of a cap. With
increasing near-surface moisture (dewpoints more into the low 60s),
we likely will need to keep an eye on at least the potential for
diurnal showers and thunderstorms starting as early as Friday, but
more likely Saturday onwards. This activity of course would not
provide any widespread drought relief, but very well could in
isolated areas. Downpours may be pretty efficient due to seasonably
high precipitable water values (~1.5"; ~90th percentile of
climatology) and deep warm cloud depths.


Gosselin

&&

.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1212 PM CDT Tue Sep 9 2025

Dry/VFR conditions with light winds are expected through Wednesday
afternoon with SCT-BKN midlevel clouds at times.

Gosselin

&&

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

$$

WFO LSX