Florissant, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

171
FXUS63 KLSX 061705
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
1205 PM CDT Tue Oct 6 2026

.KEY MESSAGES...

- Minimal/no precipitation and above average temperatures are
  forecast through this week.

&&

.SHORT TERM /THROUGH WEDNESDAY/...
Issued at 213 AM CDT Tue Oct 6 2026

As a surface high pressure center further departs, ensuing weak low-
level south/southwesterly WAA and unmitigated insolation with clear
skies will provide warmer high temperatures than Tuesday in the
upper 70s to low-80s F. Although mostly clear skies will be
favorable for efficient radiational cooling again tonight, a
gradually tightening surface pressure gradient will keep the
boundary layer from decoupling as quickly, resulting in milder low
temperatures mainly in the 50s F.

On Wednesday, an upper-level trough within northwesterly flow will
track across southern Canada and the Upper Great Lakes, forcing a
cold front southeastward through the CWA during the day. There are
some frontal passage timing differences across model guidance, but
most of the CWA is forecast to be along or ahead of the front
through peak daytime heating. This factor, coupled with strong
insolation and favorable low-level southwesterly flow/WAA, including
some potential downsloping off the Ozark Plateau, gives strong
support for well-above average high temperatures in the 80s F. None
of the HREF or global model ensemble membership have any
precipitation with the front, owing to weak large-scale forcing,
modest moisture return, and a capping inversion counteracting any
attempt at precipitation development with the front itself.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Issued at 213 AM CDT Tue Oct 6 2026

On Thursday, the front is progged to stall south of the CWA,
somewhere across southern MO or AR, but even behind the front
temperatures will remain above average with the core of the cooler
post-frontal airmass only glancing the CWA to the north and
northeast. This front will begin to lift back northward Thursday
night through Friday in response to surface cyclogenesis across the
Northern High Plains and/or Alberta. Around 20 percent of ensemble
model membership has a few showers, perhaps a thunderstorm
developing Friday morning across northeastern MO/west-central IL
with strengthening low-level WAA and a LLJ, but limited moisture and
the WAA maximum focused over the Central Plains and Upper Midwest
decreases confidence in precipitation.

Global model guidance is in agreement that the large-scale upper-
level flow pattern will change and amplify over the weekend into
early next week as a ridge migrates from the central to eastern
CONUS and a trough deepens near the West Coast. However, a
significant source of forecast uncertainty is the evolution of
Invest-92L in the eastern Gulf of Mexico as it likely (80 percent
chance per NHC) becomes a tropical cyclone and is steered northward
by a subtropical upper-level high across the Atlantic Ocean while
interacting with an upper-level low near the Southern Plains. After
potential landfall on the northern Gulf Coast, most of the latest
global and tropical-cyclone ensemble and deterministic guidance
eventually curves 92L south and southeast of the CWA over the
weekend and/or early next week. However, since the tropical cyclone
has not yet formed and there will be multiple factors dictating its
track, guidance is likely not truly representative of the range of
scenarios. This consideration means that a more northerly track into
the Mid-Mississippi River Valley still cannot be ruled out at this
range. With the impact of cloud cover and any precipitation,
temperatures are not certain over the weekend into early next week,
but nearly the entire NBM distribution remains above average.

&&

.AVIATION /12Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1200 PM CDT Tue Oct 6 2026

Today: All TAF sites are VFR this afternoon with winds
generally out of the south. Surface high pressure is currently
located over the OH/ PA border and is forecast to slowly move
east. As this occurs, winds will veer around from the
southwest. High pressure (and the resultant ridge axis) will
likely still be close enough to allow winds to go calm in the
river valleys while not going completely calm at KUIN, KCOU, and
KSTL. There will also be another round of river valley fog
possible at KSUS.

Wednesday: A cold front will approach the TAF sites from the
northwest with winds turning from the southwest. VFR.

&&

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

&&

$$

SHORT TERM...Pfahler
LONG TERM...Pfahler
AVIATION...BAH