629
FXUS63 KLSX 011739
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1239 PM CDT Fri Aug 1 2025

.KEY MESSAGES...

- Smoke from Western U.S. and Canadian wildfires will lead to
  reductions in visibility and air quality issues through today.

- Relatively cooler and dry weather is expected across the region
  through the weekend and early next week.


&&

.SHORT TERM... (Through Saturday Night)
Issued at 231 AM CDT Fri Aug 1 2025

Early morning water vapor imagery shows northwesterly flow over the
Middle Mississippi Valley as upper-level troughing continues to edge
into the Northeast. This northwesterly flow will persist through the
day, pushing the mid-week cold front further southward as high
pressure edges into the region at the surface. With low-level winds
northeasterly along the southern periphery of the high, drier air
will advect into the region, pairing with the relatively cooler post-
frontal air to lead to a fairly comfortable day by summer standards.

One negative to this pattern is the advection of wild fire smoke
from western states and Canadian wildfires into the region. Some of
this smoke has made it to the surface early this morning and is
trapped beneath the nocturnal inversion, reducing visibilities
roughly along and north of I-70. As day time heating commences and
boundary layer mixing ramps up, the surface smoke is expected to
become increasingly diffuse, but to what extent remains uncertain.
There will be plenty of smoke aloft, producing at least a hazy look
to the sky. With ample mixing expected through the day, periods of
reduced visibility and air quality issues will occur across the
area.

With the pattern holding through Saturday, much of a repeat of
Friday`s weather is expected. Afternoon highs look to be a couple
degrees cooler than Friday, however, as the area of high pressure
edges a little more southward. How the smoke forecast plays out for
Saturday is uncertain at this time range, and will come into better
view this evening and tonight.

Elmore

&&

.LONG TERM... (Sunday through Thursday)
Issued at 231 AM CDT Fri Aug 1 2025

Northwesterly flow is still expected over the CWA at the start of
the extended period per guidance consensus. Within this flow, a
shortwave will move into the Middle Mississippi Valley, with rain
moving eastward across the Great Plains toward the region. However,
stubborn high pressure at the surface will keep conditions
unfavorable for rainfall locally, with a majority of global ensemble
members showing rainfall through the end of the weekend.

Starting Monday and continuing through the end of the period, both
deterministic guidance and ensemble clusters show an upper-level
ridge amplifying over the western CONUS. A majority of guidance
keeps the ridge centered well west of the region, with our CWA
remaining beneath some degree of north-northwesterly flow on the
eastern periphery of the ridge. While this will keep the more
notable heat west of the region, the positioning of the ridge will
allow for southerly flow near the surface, which will provide warm
air advection in the low to mid levels. In response, our
temperatures will gradually climb back to climatological normals
(highs in the upper 80s, lows in the mid 60s) by the middle to end
of next week; though, how warm exactly will be dependent on the
specific positioning of the ridge which is currently uncertain. If
the ridge is able to build more eastward than expected, we could see
temperatures up to approximately 5 degrees warmer than currently
forecast. The return of southerly low-level flow paired with
transpiration from area crops will cause an uptick in humidity as
well, though current indications are that the level of heat and
humidity will fall short of our most recent stretch.

With the increase in heat and humidity will come an gradual increase
in the chance for showers and thunderstorms. Even so, with a lack of
forcing or defined triggers, the daily chances remain low (around
20%) and nebulous. Confidence is high that most locations will
remain dry through the extended forecast period.

Elmore

&&

.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1236 PM CDT Fri Aug 1 2025

Dry northeast flow keeps a mostly clear sky around tonight and
tomorrow. The only exception is some wildfire smoke which has
circled around and made it into the region. This may cause periods
of limited visibility, but will likely remain in the MVFR range at
worst. The most likely time for these lower visibilities is in
the morning hours before stronger low level mixing begins, though
confidence in this occurring is too low to include in the TAFs
right now.

Kimble

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX