789
FXUS63 KLSX 081143
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
643 AM CDT Mon Jun 8 2026

.KEY MESSAGES...

- Scattered showers and thunderstorms are expected through the day today.
  All thunderstorms will be capable of locally heavy rainfall and
  flash flooding.

- A thunderstorm or two over portions of southwestern Illinois
  and southeastern Missouri will be capable of damaging wind gusts
  and tornadoes this afternoon.

- Temperatures will climb into the 90s Tuesday-Thursday. This
  heat will combine with humidity to produce heat index values of
  100-105 at least Tuesday and Wednesday.


&&

.SHORT TERM... (Through Tonight)
Issued at 350 AM CDT Mon Jun 8 2026

The cutoff responsible for our rain chances as of late can be seen
in water vapor imagery passing through the Middle Mississippi Valley
this morning. Nebulous lift from the cutoff and a low-level jet will
continue to force widely scattered convection across the CWA through
the morning hours. As we approach peak heating this afternoon, the
cutoff will become increasingly fractured, with a lobe of vorticity
pivoting along its southern flank over the CWA. This will cause an
uptick in convective coverage and intensity for areas mainly along
the Mississippi River and eastward. With PWAT continuing to hover
around 2", a deep warm cloud layer, and the potential for training,
the threat for flash flooding will continue today, and has prompted
an expansion of the Flash Flood Watch where confidence is greatest
in isolated to scattered impacts.

Across southeastern Missouri and southwestern Illinois, lift will be
maximized among deep layer shear of 25-30 kts and 0-1km shear of 15-
20 kts. This will allow for some updraft organization and longevity,
leading to a chance of isolated strong to severe thunderstorms
capable primarily of damaging wind gusts. The low-level shear
produces a low chance for a tornado or two, especially for longer-
lived storms and those that are able to interact with outflow
boundaries. Waning instability and rising heights this evening will
lead to a gradual decrease in convective coverage and intensity.

Elmore

&&

.LONG TERM... (Tuesday through Sunday)
Issued at 350 AM CDT Mon Jun 8 2026

The primary focus for impacts Tuesday and Wednesday is the potential
for dangerous heat. In the wake of the cutoff that has been plaguing
the Midwest this past weekend and early week period, ensemble
consensus is that upper-level ridging will quickly build into the
region on Tuesday. Deep southwesterly flow will advect warm air into
the Middle Mississippi Valley as 850 mb temperatures see a 6-7 C
jump compared to values in the days prior, with ensembles favoring
values around 21-22 C. This climatologically supports surface
temperatures topping out in the low 90s F, which matches well with
the NBM forecasted high temperatures on Tuesday. While ensembles
keep 850 mb temperatures around these levels through Wednesday,
Wednesday`s high temperatures are expected to be a couple of degrees
warmer than Tuesday`s thanks to a warmer start to the day and less
cloud cover. With dew points expected to be in the mid 70s, heat
index values will climb to around 100 degrees for most locations,
with some locations seeing as high as 105 degrees. This magnitude of
heat would warrant a Heat Advisory for portions of the area, and
decisions on such a headline will be made in the next 24 hours.

While some guidance has this level of heat carrying into Thursday,
confidence in this outcome is low thanks to a front approaching the
area as upper-level troughing expands across the northern half of
the CONUS. While the consensus is for a FROPA after peak heating,
cloud cover and convection may reduce insolation enough to take the
edge off the heat. The convection has the potential to be severe for
portions of the Middle Mississippi Valley, as it will be occurring
in an environment characterized by around 2,000 J/kg of SBCAPE and
30-35 kts of deep-layer shear per ensemble means. There is still
enough spread in the front`s timing and the phasing of a leading
shortwave that severe thunderstorms in our CWA are far from a
guarantee.

In the wake of the front Friday into the weekend, ensemble clusters
and deterministic guidance show zonal flow over the Middle
Mississippi Valley. This will at least favor cooler temperatures
than what will be experienced earlier in the week. However, this
does also open the door for unsettled weather, with deterministic and
ensemble solutions showing a wide variety of outcomes. As a result,
the NBM/current forecast has continuous PoPs through the weekend.
While this makes it difficult to hone in on specifics, a majority of
solutions show predominantly dry conditions this weekend outside of
relatively brief rain chances.

Elmore

&&

.AVIATION...  (For the 12z TAFs through 12z Tuesday Morning)
Issued at 627 AM CDT Mon Jun 8 2026

Multiple rounds of scattered showers and thunderstorms are
expected through today. An initial round is moving through the
region this morning, with confidence greatest in direct impacts at
KCOU, KJEF, KSUS, KSTL, and KCPS. There is a very low chance for
impacts at KUIN earlier than what is forecast. Another round is
expected this afternoon, with impacts most likely confined to
KSUS, KSTL, and KCPS. Recent trends suggest that this second round
may form just east of these three sites, leading to little to no
impacts. There is a very low chance of thunderstorms at KJEF and
KCOU at the very end of the period, with confidence too low in
impacts to mention in this round of TAFs.

Elmore

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Flood Watch through late tonight for Franklin MO-Gasconade MO-
     Jefferson MO-Lincoln MO-Montgomery MO-Pike MO-Saint Charles
     MO-Saint Louis City MO-Saint Louis MO-Warren MO.

     Flood Watch until 1 PM CDT this afternoon for Audrain MO-Boone
     MO-Callaway MO-Cole MO-Knox MO-Lewis MO-Marion MO-Moniteau
     MO-Monroe MO-Osage MO-Ralls MO-Shelby MO.

IL...Flood Watch through late tonight for Bond IL-Brown IL-Calhoun IL-
     Clinton IL-Fayette IL-Greene IL-Jersey IL-Macoupin IL-
     Madison IL-Marion IL-Monroe IL-Montgomery IL-Pike IL-Saint
     Clair IL-Washington IL.

     Flood Watch until 1 PM CDT this afternoon for Adams IL.

&&

$$

WFO LSX