382
FXUS63 KLSX 010746
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
246 AM CDT Tue Jul 1 2025

.KEY MESSAGES...

- Seasonal temperatures (upper 80s to near 90 degrees) follow a
  cold front today and persist through Thursday. Warmer air
  gradually returns for the July 4th holiday into next weekend.

- Dry conditions are expected through Friday. Precipitation
  chances increase over the weekend with an active pattern favored
  early next week.


&&

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 245 AM CDT Tue Jul 1 2025

Surface low pressure continues move eastward as a cold front
advances southeast through the region early this morning. IR
satellite shows broken cloud cover accompanying the front with
latest radar mosaics showing much of the measurable precipitation
near the Illinois/Indiana border. A few showers may pop along the
front with potential trending lowers as the front clears to the
south and east.

Conditions are expected to continue to improve overall with one
caveat early this morning. Patchy fog may develop in low-lying
areas, especially where dense vegetation retains moisture from
recent rainfall. Surface analysis shows surface moisture lagging
behind the front with dewpoints in the mid/upper 60s extending into
southern Iowa/eastern Kansas. There is a brief window when clouds
clear, surface winds calm and narrow dewpoint depressions could
support patchy fog where ground moisture remains high from last
evening`s rainfall. Much of this will be limited in time and
geographical extent, eroding quickly after sunrise. Observations out
of Kirksville provide a good example of this with a very brief
episode of 1/4SM visibility that has since become absent.

Conditions will be relatively exceptional today through Wednesday as
upstream dewpoints in the low-60s filter down via northwest flow.
Surface high pressure moves overhead, providing insurance for a dry
forecast with high temperatures (mid/upper 80s) a touch cooler than
previous days. The sensible change will be the decreasing moisture
that brings a couple days of relief from the more oppressive
dewpoints that were in the low/mid-70s. Nighttime periods may even
feel somewhat crisp in comparison, as low temperatures tuck just
under 70 degrees in urban areas and outlying locations drop well
into the 60s Wednesday and Thursday morning.


Maples

&&

.LONG TERM...  (Wednesday Night through Monday)
Issued at 245 AM CDT Tue Jul 1 2025

Long Term (12z Thursday-Monday)

Surface high pressure will continue to maintain dry conditions
Thursday as an amplified upper ridge to our west slowly builds
eastward through the later portion of the week. The eastward
translation is both features will result in a slight bump in
temperatures Thursday, but still near seasonal norms with high
temperatures in the upper 80s to low-90s.

The sensible change from Thursday into the July 4th holiday will be
the result of increasing moisture in conjunction with yet another
slight bump in temperatures. Thursday`s 80s give way to widespread
low to mid-90s as the surface high moves far enough east to result
in southerly return flow. Moisture begins to increase from west to
east with the corridor of 70+ degree dewpoints encroaching on the
Mississippi River through Friday afternoon. Overall, still not too
bad of a deal considering the rain-free scenario that will serve as
a compliment to outdoor activities. That being said, heat index
values could flirt with 100 degrees in urban areas during peak
heating. Hydration remains key to staving off potential for minor
heat-related issues given the plans that may include a long duration
of time spent outdoors.

There is high confidence that heat returns over the weekend, but the
magnitude of heat isn`t likely to rival that which was felt last
week. EOF patterns show little/no variability in the mean H5
pressure patterns with an expansive upper ridge encompassing
approximately 2/3rds of the eastern CONUS. LREF probabilities show
low chances (20-40%) for temperatures greater than 90 degrees co-
located with dewpoints above 70 degrees.

Meanwhile, an upper level shortwave traverses the northern U.S. from
west to east, drawing a cold front into the central U.S. sometime
late next weekend. Much of the support for widespread precipitation
will remain well north of the area with local rain chances largely
driven by surface/mid-level features. Southwesterly flow strengthens
in this timeframe, solidifying trends in the return of a warm and
moist airmass. Much of what occurs ahead of the front is likely to
be diurnally driven in the absence of any broad scale upper ascent.
Potential is likely to increase as the front arrive sometime late
Saturday into Sunday, then stalls somewhere across the central U.S.,
resulting in what could be a more active pattern early next week.


Maples

&&

.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1137 PM CDT Mon Jun 30 2025

A cold front is progressing through the region from northwest to
southeast, which will draw drier air in through Tuesday. Aside
from the wind shift behind the front, impacts are limited to fog
potential tonight into early Tuesday morning. Much of this
potential will more likely be realized in low-lying areas with
dense vegetation, as the canopy of vegetation retains moisture
from recent rainfall. A TEMPO group addresses this potential at
KJEF, while the probability for fog is lower at other terminals.
It wouldn`t be all that surprising if KSUS/KCPS needed TEMPO
groups in later amendments, pending the speed of the front and
drier air. This will be closely monitored overnight in the event
amendments are needed.

VFR conditions are otherwise favored outside of fog potential as
winds shift out of the northwest Tuesday.

Maples

&&

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

$$

WFO LSX