Florissant, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

547
FXUS63 KLSX 282320
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
620 PM CDT Sun Jun 28 2026

.KEY MESSAGES...

- Dangerous levels of heat and humidity are expected through this
  week.


&&

.SHORT TERM...  (Through Late Monday Night)
Issued at 159 PM CDT Sun Jun 28 2026

Afternoon water vapor imagery shows an upper-level ridge quickly
amplifying over the eastern CONUS, with surface obs showing last
night`s warm front having lifted well north-northeastward of the
CWA. This has opened the door to robust warm air advection, pairing
with ample insolation to push temperatures in to the upper 80s and
low 90s across the CWA. With a few more hours of peak heating left,
temperatures are expected to rise further into the mid 90s. When
paired with the humidity across the region, heat index values are
mostly in the 100-105 degree range and dangerous for those with
prolonged exposure. The ridge only builds further northward on
Monday, leading to high confidence in another day of dangerous heat.
Temperatures will be a few degrees warmer thanks to lows only
bottoming out in the mid to upper 70s tonight.

Elmore

&&

.LONG TERM...  (Tuesday through Next Sunday)
Issued at 159 PM CDT Sun Jun 28 2026

By the start of the long-range forecast period Tuesday morning,
guidance consensus is that the upper-level ridge will have amplified
to its northern-most latitude across the eastern CONUS. While a
majority of global ensemble members have 850mb temperatures being at
their warmest through this portion of the period on Tuesday, the
gradual, subtle cooling through Saturday is expected to have an
unnoticeable effect on surface temperatures thanks to the hot start to
the week. The main impact of these slightly cooler 850 mb
temperatures will be a more favorable thermal profile for air mass
thunderstorms Thursday into Saturday. Given the brief, isolated
nature of this potential convection, it is not expected to provide
notable heat relief. There is at least a medium chance that heat
headlines will be extended into Saturday, with the need for this
being assessed with each forecast package.

Ensemble clusters show the ridge retrograding westward for Sunday,
with deterministic guidance showing a shortwave passing through the
Midwest. Both factors favor at least some degree of cooling through
height falls and/or a cold FROPA; however, specifics at this lead
time are highly uncertain. While ensemble spread in surface
temperatures increases on Sunday in response to this uncertainty,
the 25th percentile of high temperatures is in the upper 80s,
supporting a continuation of summer-like warmth.

Elmore

&&

.AVIATION...  (For the 00z TAFs through 00z Monday Evening)
Issued at 615 PM CDT Sun Jun 28 2026

VFR flight conditions are expected to prevail through the period.
Gusty southerly flow will diminish this evening. Gusts will resume
late Monday morning into the afternoon.

Carney

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Heat Advisory until midnight CDT Thursday night for Audrain MO-
     Boone MO-Callaway MO-Cole MO-Crawford MO-Gasconade MO-Iron
     MO-Knox MO-Lewis MO-Lincoln MO-Madison MO-Marion MO-
     Moniteau MO-Monroe MO-Montgomery MO-Osage MO-Pike MO-Ralls
     MO-Reynolds MO-Saint Francois MO-Shelby MO-Washington MO.

     Extreme Heat Warning until midnight CDT Thursday night for
     Franklin MO-Jefferson MO-Saint Charles MO-Saint Louis City
     MO-Saint Louis MO-Sainte Genevieve MO-Warren MO.

IL...Heat Advisory until midnight CDT Thursday night for Adams IL-
     Bond IL-Brown IL-Calhoun IL-Fayette IL-Greene IL-Jersey IL-
     Macoupin IL-Marion IL-Montgomery IL-Pike IL.

     Extreme Heat Warning until midnight CDT Thursday night for
     Clinton IL-Madison IL-Monroe IL-Randolph IL-Saint Clair IL-
     Washington IL.

&&

$$

WFO LSX