O'Fallon, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

733
FXUS63 KLSX 100323
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1023 PM CDT Mon Jun 9 2025

.KEY MESSAGES...

- Quiet and dry conditions are expected tomorrow and Wednesday,
  and likely Thursday as well.

- A warming trend is increasingly likely late in the work week,
  with temperatures climbing back to near or slightly above
  average, and potentially touching 90 degrees.

- Active and showery conditions are likely to return Friday
  through the weekend, although confidence is somewhat low
  regarding exactly when precipitation will return.


&&

.SHORT TERM...  (Through Late Tuesday Night)
Issued at 126 PM CDT Mon Jun 9 2025

Mild and dry conditions have settled in for a few days across the
area thanks to northwest flow and a continental post-frontal
airmass. While some sporadic cumulus is evident on visible
satellite in a few areas, and there is some high resolution
guidance that suggests that a few very weak showers may develop
later in the afternoon, it`s very unlikely that this activity
would amount to much more than virga or perhaps a few sprinkles.
Otherwise, the other item of note for today is the development of
breezy westerly winds, which are expected to continue the
remainder of the afternoon and diminish in the evening.

This pattern is expected to continue through tomorrow as well,
although a reduced pressure gradient is likely to result in weaker
wind speeds. With temperatures forecast to reach near 80 degrees and
dewpoints in the upper 50s to low 60s, tomorrow is expected to be a
comfortable day throughout the area, with sunny skies also likely to
persist.

BRC

&&

.LONG TERM...  (Wednesday through Next Monday)
Issued at 126 PM CDT Mon Jun 9 2025

As we head into the middle of the week, an upper level ridge is
expected to slowly build east and into the area, and persistent
southerly low level flow will develop as well. Initially this is
expected to produce a modest warmup beginning Wednesday, with
ensemble mean temperatures generally in the mid to upper 80s area-
wide. Confidence is slightly higher that these warmer values will be
realized as guidance has slowed the arrival of higher humidity and
precipitation, and we may even make a run at 90 degrees in a few
spots. Similar temperatures are increasingly likely Thursday as
well, which continues to trend drier and drier.

From Friday onward though, ensemble guidance continues to depict a
northward surge in rich moisture, bringing the return of shower and
thunderstorm chances to the area. Ensemble mean precipitable
water values continue to be projected near or slightly higher than
the 90th percentile of climatology, which this time of year is
roughly 1.6 inches. However, this influx of moisture continues to
gradually slow down in ensemble projections, and the core of this
airmass remains slightly to our south.

Regardless, precipitation chances do steadily increase Friday
through the weekend, although the day to day probabilities fluctuate
considerably due to the influence of a subtropical wave undercutting
the longwave ridge. This feature, along with other smaller scale
impulses, are likely to provide a modest forcing boost that will
dictate when and where showers and thunderstorms form, and likewise
which areas will see the most rainfall. Given the projected moisture
parameters, localized pockets of heavy rain will at least be
possible, but whether or not this will have the potential to produce
more than just beneficial rain remains to be seen due to the heavy
influence of smaller scale features.

Meanwhile, ensembles also project increasing instability throughout
this period, but with the longwave ridge overhead, the most
significant wind shear is likely to exist farther north near the
primary jet stream. Likewise, higher probabilities for severe
thunderstorms exist farther to the north during this timeframe, most
notably across the northern Plains and upper Mississippi Valley
regions. Still, given the influx of moisture and increasing
instability potential, we can`t completely rule out some low-end
probabilities due to local mid level flow enhancements from the
subtropical wave.

Finally, temperature forecasts late in the week become a bit less
certain thanks to the influence of increasing cloud cover and
precipitation, but current ensemble mean projections remain very
near seasonal averages. Likewise, forecast temperature spreads
increase during this period, as this is a direct result of the
uncertainty surrounding day to day rounds of precipitation.

BRC

&&

.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1021 PM CDT Mon Jun 9 2025

Dry and VFR conditions are expected through the period. Winds will
be mainly light and variable, though they will turn out of the
west around 6 knots during the day on Tuesday at UIN.

Britt

&&

.CLIMATE...
Issued at 227 PM CDT Fri Jun 6 2025

St Louis has still not seen 90 degrees yet in 2025. The average
first 90 degree reading is May 20. The most recent late 90-degree
start was June 10, 2021. If St Louis doesn`t hit 90 by June 10,
it will be the latest first 90 degree day since at least 1995
(June 19). The latest date of first 90 degrees on record was July
4 in both 1961 and 1912.

Columbia has also not yet seen a 90 degree reading in 2025, however
the average first date is much later (May 31). The latest date of
first 90 degrees on record was July 14, 1904.

Quincy reached 90 degrees on May 15 of this year, about 3 weeks
earlier than their average first 90 degrees (June 2).

Kimble


&&

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

$$

WFO LSX