941
FXUS63 KLSX 101122
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
622 AM CDT Mon Aug 10 2026

.KEY MESSAGES...

- Dangerous heat and humidity expected to continue through
  Wednesday. Extreme Heat Warnings and Heat Advisories remain in
  effect.

- An approaching cold front brings chances for rain and a cool
  down on Wednesday through the end of the week. However, there
  are indications that above average temperatures could still
  persist beyond Wednesday.

&&

.SHORT TERM /THROUGH TUESDAY/...
Issued at 405 AM CDT Mon Aug 10 2026

Upper and mid level water vapor imagery from GOES East
indicates the presence of a shortwave over the Mississippi River
Valley. The shortwave combined with a low-level jet over
western MO are providing the lift needed to support the ongoing
convection in western and central MO. This convection will
remain in an area of 2000+ kg/J MLCAPE and 30-35 kts 0-1km wind
shear allowing it to hold together, possibly making it into our
western most counties before dissipating into weak showers.
Several CAMS are indicating that these showers will be isolated
along and north of the I-70 corridor during the morning hours.
These thunderstorms and showers are not expected to be severe
due to a weakening low-level jet.

An upper level ridge remains over the region and continues to
allow low-level southerly flow, which will result in the heat
and humidity to remain over the region. Model guidance continues
to show 850mb temperatures remaining high (above 95th
climatological percentile) at 22-25C, translating to surface
temperatures in the mid to upper 90s F. The cloud cover
associated with the isolated showers and thunderstorms this
morning in northeastern MO and west central IL will keep
temperatures a few degrees lower than the rest of the region,
but moisture pooling along a stationary front in northern MO and
southern IA will keep the dewpoints a few degrees higher. This
will keep the heat index values high in that area. These hot
temperatures combined with dewpoints in the mid-70s will result
in heat index values reaching 100-110 F in the afternoon, with
the highest values along the I-70 corridor and southwestern IL.
Tonight will remain dry, but the high dewpoints will result in a
muggy night through the region. Tuesday the story is the same,
with air temperatures in the mid to upper 90s with mid-70s
dewpoints across the region resulting in 100-110 F heat index
values. Due to these forecasted temperatures, no changes were
made to the Extreme Heat Warning and Heat Advisory.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Issued at 405 AM CDT Mon Aug 10 2026

Ensemble guidance continues to show chances of rain Wednesday
night and into Thursday due to forcing driven by upper-level
divergence, low-level warm air advection, and a shortwave over
northern IL and southern WI, although estimated rainfall totals
are trending down. Current guidance is indicating rainfall
totals of 0.1 to 0.5 inches in the northern part of our forecast
region, while the southern part of the forecast region may only
see closer to 0.1. As a result, dangerous heat and humidity
will continue to impact the region on Wednesday.

The latest guidance is continuing to agree that an upper level
ridge will remain over the Mid-Mississippi Valley Thursday
through the weekend. As a result, the cold front that was
expected to move into the region may not make it as far south as
initially expected, stalling in far northern MO and southern IA.
Northeastern MO and west-central IL could see some minor relief,
dropping temperatures several degrees compared to the rest of
our forecast area. Despite the potential relief, potentially
impactful heat may return this weekend by the weekend, but
confidence is low with temperature IQRs of 10-15 degrees
Thursday through Sunday due to the uncertainty in how far south
the cold front progresses. Meanwhile the guidance is indicating
that the temperatures for the rest of our region could be
comparable with the temperatures we have seen over the last
couple of days. The rainfall forecast for the region has also
been impacted due to the cold front forecasted to remain farther
north than previously forecasted, with cluster analysis
providing higher confidence that the swath of heavy rain
remaining more north in southern IA.

&&

.AVIATION /12Z TAFS THROUGH 18Z TUESDAY/...
Issued at 618 AM CDT Mon Aug 10 2026

An axis of showers and weak thunderstorms developed over the
last few hours at the St. Louis terminals and across central
Missouri. While VFR CIGs/VSBYs do exist, this convection will
pester the terminals through the next hour or so. Afterwards,
dry and VFR conditions will prevail through the remainder of the
period with a gusty southwest wind developing this afternoon.

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Heat Advisory until 8 PM CDT Wednesday for MOZ018-019-026-027-
     034>036-042-052-072>075-084-085-099.
     Extreme Heat Warning until 8 PM CDT Wednesday for MOZ041-
     047>051-059>065.
IL...Heat Advisory until 8 PM CDT Wednesday for ILZ058>060-064-065-
     070-095>099.
     Extreme Heat Warning until 8 PM CDT Wednesday for ILZ069-074-
     079-100>102.

&&

$$

SHORT TERM...Asel/MRB
LONG TERM...Asel/MRB
AVIATION...MRB