014
FXUS63 KLSX 281147
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
647 AM CDT Tue Jul 28 2026

.KEY MESSAGES...

- Hot and humid weather will continue today along and south of
  I-70 ahead of a cold front. The heat index is expected to
  climb to between 100 and 108 degrees in these areas.

- There is a chance that clouds and showers will move into the
  area from the west and bring an early end to this recent
  period of excessive heat.

- Temperatures are expected to be near to below normal for the
  remainder of the forecast period. The next significant chance
  for rain for the area will begin Thursday night and continue
  through Saturday.

&&

.SHORT TERM /THROUGH WEDNESDAY/...
Issued at 333 AM CDT Tue Jul 28 2026

Low pressure will move through the Ohio Valley today and drag a cold
front south and west through Illinois and into western Missouri or
eastern Kansas over the next 48 hours.  Relief from the oppressive
heat and humidity will begin today across much of northeast Missouri
into west central and south central Illinois, however the remainder
of the forecast area will likely continue to see heat index readings
above 100 degrees this afternoon.  Therefore the Heat Advisory
continues along the Missouri River and along and just south of I-70
in Illinois.  It still looks a little warmer and more humid with
heat index readings topping 105 across southeast Missouri and
southern Illinois, so the Extreme Heat Warning continues in these
locations as well.

With that in mind, there is the potential for cooler temperatures
and rain across much of the advisory/warning area today as a short
wave trough moves from the Great Plains into Missouri. This wave is
currently producing a broad area of showers and thunderstorms across
Kansas and Nebraska. Most deterministic guidance shows this
precipitation weakening and decreasing in areal coverage through
this morning, however some models including most CAMs show at least
some light showers moving across central and southeast Missouri from
mid morning through the afternoon.  If there is precip as the CAMs
suggest, or if there`s even a significant amount of cloud cover,
temperatures will likely be several degrees cooler than forecast
which will allow heat headlines to be cancelled early.  Regardless,
there could be widely scattered thunderstorms later this afternoon
into early evening if there is sufficient heating ahead of the front
as GFS and RAP soundings show 2000-2500 J/Kg CAPE.  The models are
also showing around 30kts of deep-layer shear, so there could be
some strong to marginally severe wind gusts if storms can actually
develop.

The front continues moving southwest tonight into Wednesday, and a
cooler and drier airmass moves into the Mid Mississippi Valley.  The
NBM shows dew point temperatures dropping into the mid 60s by
Wednesday afternoon, and the GFS and RAP are even lower in the mid
to upper 50s.  Regardless, temperatures should be several degrees
cooler in the mid to upper 80s in most locations.  This will bring
a decisive end to this recent period of excessive heat.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Issued at 333 AM CDT Tue Jul 28 2026

High pressure remains over the Mid Mississippi Valley on Thursday,
and then drifts east Thursday night into Friday. Meanwhile, an upper
level short wave moves into the Midwest Thursday into Thursday
night.  The wave deepens into a closed low over southern Minnesota
by 12Z Friday.  The low moves slowly southeast across the
Mississippi Valley through the weekend, finally stalling over
western Kentucky or far southeast Missouri Sunday evening.  The
deterministic GFS and ECMWF are in good agreement with the speed and
track low through this period, and both produce periods of precip
Friday through Sunday.  Clouds and periods of rain associated with
the low leads to below normal temperatures in most locations through
Monday.  Guidance diverges on the position of the cut off low aloft
by late Monday into Tuesday with the GFS showing it almost directly
over St. Louis by 18Z Tuesday and the ECMWF putting it over
northwest Tennessee.  While there are differences in strength and
position of the low apparent in the deterministic guidance Friday
through Tuesday, the 4 LREF clusters show a very similar synoptic
pattern through the period.  This leads to relatively high
confidence in precipitation chances for Friday and Saturday as the
low passes across the area.  Individual high temperatures are
somewhat less certain Friday through Tuesday, and will ultimately
depend on cloud cover and duration of precip each day. This is
illustrated by 5-8 degree interquartile high temperature ranges each
day, though even the 75th percentile is below normal.

&&

.AVIATION /12Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 638 AM CDT Tue Jul 28 2026

VFR flight conditions are expected to prevail through the
period. An upper level disturbance will move from northwest to
southeast across Missouri today. This disturbance is producing
some showers and a few thunderstorms across parts of western
Missouri at this time. This activity is diminishing as it
progresses southeast, although it is unclear if this trend will
continue or if there will be some restrengthening today. At any
rate, there is a chance for showers and a few thunderstorms
across central and southeast Missouri today as the disturbance
moves through. Visibilities may be reduced to MVFR or possibly
IFR briefly if the precipitation can restrengthen today.
Otherwise...northwest wind will veer to the north, and then
northeast and east through the period as a "back door" cold
front moves from Illinois into Missouri today and tonight.

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Heat Advisory until 7 PM CDT this evening for MOZ041-047>052-
     059>064.
     Extreme Heat Warning until 7 PM CDT this evening for MOZ065-
     072>075-084-085-099.
IL...Heat Advisory until 7 PM CDT this evening for ILZ064-069-070-
     100.
     Extreme Heat Warning until 7 PM CDT this evening for ILZ074-
     079-101-102.

&&

$$

SHORT TERM...Carney
LONG TERM...Carney
AVIATION...Carney