Florissant, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

806
FXUS63 KLSX 150318
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1018 PM CDT Tue Oct 14 2025

.KEY MESSAGES...

- Seasonably warm temperatures will continue through Friday.

- Widespread showers and isolated thunderstorms are expected late
  Friday night - Saturday. This should provide at least some
  beneficial rainfall to the region, with a very conditional
  threat for a few strong to severe thunderstorms.


&&

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 244 PM CDT Tue Oct 14 2025

A weak warm front near the Missouri-Iowa border is expected to
shift off to the north tonight, with weak surface ridging in its
wake. Some midlevel clouds should continue to move across
northeast Missouri and west-central Illinois through Wednesday,
with more clearing the further south you travel. Lows are forecast
to be in the mid 50s in southeast Missouri and south-central
Illinois, with some spots of low 50s possible in river valleys.
Further north/northwest, more clouds should keep temperatures from
dropping below the 60 degree mark.

Highs on Wednesday should be a tick or two higher than this
afternoon, with most locations topping out in the low to mid 80s.
Those readings would be about 15 degrees above normal for the middle
of October.


Gosselin

&&

.LONG TERM...  (Wednesday Night through Next Tuesday)
Issued at 244 PM CDT Tue Oct 14 2025

(Wednesday Night - Friday)

The persistent warm, dry pattern should continue through the end of
the work week given anomalous mid/upper level ridging over the
region. Temperatures are expected to remain about 10-15 degrees
above normal day and night with highs mostly in the low 80s and lows
ranging from the mid 50s to low 60s.


(Friday Night - Saturday Night)

There remains a very good signal for a widespread beneficial
rainfall impacting the area late Friday night into Saturday as a
cold front slowly moves through the bi-state area. While there is
still some spread with respect to the timing of the synoptic cold
front and the track/timing of a secondary midlevel shortwave trough,
there is good agreement in the late Friday night into Saturday
morning time frame. Deterministic guidance all shows increasing low-
level moisture advection concurrently with increasing ascent
downstream of a midlevel disturbance and upper-level divergence via
jet dynamics. There are even some signs of a coupled jet structure
around midday Saturday.

Spread increases Saturday afternoon as a secondary midlevel
shortwave trough should eject out of the south-central Plains. This
feature should help continue showers and isolated thunderstorms
along/ahead of the cold front, but as alluded to above, there is
still quite a bit of spread with both the track/timing of this
feature. The GFS/GEFS is further south, which decreases the midlevel
forcing for ascent in our region Saturday afternoon/evening. The
ECMWF/EPS meanwhile is a bit slower, but with a track further north
through southeast Missouri/southwest Illinois. This would tend to
keep the high coverage of showers/thunderstorms going along/ahead of
the slow moving cold front through Saturday evening (and bring us
heavier rainfall totals). Probabilities for >0.50" and >1" on the
EPS are about 10-20% higher. Regardless though, it does appear
increasingly likely that this should be the most significant
widespread rainfall across most of the region since mid/late
September. LREF probabilities for at least 0.50" of rain through
Saturday night range from 40-60% and chances for >1" being in the 10-
30% range. The other item of good news is that the southeast half of
the CWA (east central and southeast Missouri as well as southwest
Illinois) are most likely to see the higher totals at this time.
This is where it has been really dry the past 2+ months and where
there is quite a bit of D2/severe drought conditions.

One potential negative impact Saturday afternoon/evening is the
chances of a few strong to severe thunderstorms along the cold
front. There remains many negating factors, the biggest of which was
detailed above. There is a strong signal for rainfall Saturday
morning out ahead of the cold front. Six-hour probabilities on the
LREF between 12-18Z are in the 70-90% range. This antecedent rain
and associated cloud cover really cast doubt on how much instability
will be for the afternoon. Probabilities for at least 500 J/kg of
SBCAPE are only in the 10-30% range across southeast
Missouri/southwest Illinois Saturday evening and drop to ~10% or
less for >1000 J/kg. This means that any severe threat looks very
conditional at this time range, with the most likely scenario being
a widespread beneficial rainfall with embedded thunderstorms. We
will continue to keep an eye on this time period as there should be
plenty of shear available. Mean 0-6 km shear values approach 50
knots late Saturday from the LREF. Those values are high, though
nothing extraordinary either for the middle of October. As alluded
to yesterday, the orientation of the deep-layer shear vectors are
also likely to be fairly parallel to the boundary itself. This would
tend to favor more clusters of thunderstorms or line segments
instead of discrete convection (supercells).


(Sunday - Next Tuesday)

There is high confidence in a (brief) cooldown behind the cold front
to end the weekend. Temperatures are expected to get back closer to
normal for the time of year however. Ensemble guidance shows spread
in both the amplitude and timing of mid/upper level ridging moving
eastward out of the Rocky Mountains early next week. A faster
(slower) eastward progression of this ridge would lead to a quicker
(slower) warmup. Rain chances may also return by next Tuesday in the
quicker scenario as a midlevel shortwave may move out of the Plains.
Before Tuesday, there appears to be at least a 48 hour period of dry
weather on tap.


Gosselin

&&

.AVIATION...  (For the 06z TAFs through 06z Wednesday Night)
Issued at 1013 PM CDT Tue Oct 14 2025

River fog is likely to develop and affect JEF/SUS/CPS late
tonight and early on Wednesday, mainly between 08-13Z causing
visibilites AOB 1SM at times. Otherwise dry and VFR conditions are
expected with light winds.

Britt

&&

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

$$

WFO LSX