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FXUS63 KLSX 081744
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1244 PM 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 18z TAFs through 18z Tuesday Afternoon)
Issued at 1244 PM CDT Mon Jun 8 2026

Showers and thunderstorms are generally exiting St. Louis metro
terminals is the continue northeastward, but will continue to impact
portions of northeastern and south-central IL including KUIN early
this afternoon. Additional redevelopment of showers and
thunderstorms is possible later this afternoon through evening near
and east of the Mississippi River, reflected as a PROB30 group at
St. Louis metro terminals.

There is a low chance of showers and thunderstorms that persist
overnight into Tuesday morning, but confidence is low in impacts at
terminals except at KCOU and KJEF. At these terminals, there is
increasing confidence in a decaying complex of thunderstorms
arriving from the west overnight. It is uncertain if this complex
will remain in tact as it reaches St. Louis metro terminals.

Pfahler

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Flood Watch through Tuesday morning for Crawford MO-Franklin MO-
     Gasconade MO-Jefferson MO-Lincoln MO-Montgomery MO-Pike MO-
     Saint Charles MO-Saint Francois MO-Saint Louis City MO-
     Saint Louis MO-Sainte Genevieve MO-Warren MO-Washington MO.

     Heat Advisory from noon to 10 PM CDT Tuesday for Boone MO-
     Callaway MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO-
     Iron MO-Jefferson MO-Lincoln MO-Madison MO-Moniteau MO-
     Montgomery MO-Osage MO-Reynolds MO-Saint Charles MO-Saint
     Francois MO-Saint Louis City MO-Saint Louis MO-Sainte
     Genevieve MO-Warren MO-Washington 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 Tuesday morning 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-
     Randolph IL-Saint Clair IL-Washington IL.

     Heat Advisory from noon to 10 PM CDT Tuesday for Calhoun IL-
     Jersey IL-Madison IL-Monroe IL-Randolph IL-Saint Clair IL.

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

&&

$$

WFO LSX