011
FXUS63 KLOT 040751
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
251 AM CDT Mon Aug 4 2025

.KEY MESSAGES...

- 20% chance for showers/storms south of a Streator, IL to
  Fowler, IN line this afternoon.

- Hazy skies continue today due to lingering wildfire smoke.

- Additional showers/storms may develop Tuesday afternoon,
  mainly south of I-80.

- A steady increase in temperatures and humidity is expected
  through the week.

&&

.DISCUSSION...
Issued at 251 AM CDT Mon Aug 4 2025

Isolated obs this morning are showing reduced visibility down
to 5 miles with reports of either smoke or haze. Models are
still suggesting a large plume of smoke over the area today, but
the expectation is for it to remain aloft. As the mid level
flow turns to the southeast, most of the smoke closer to the
ground should scour out enough to not have any formal mention in
the forecast though a murky look to the sky is possible.

Dew point depressions are steadily decreasing this morning.
While patchy shallow fog in rural areas cannot be completely
ruled out, the only observation of patchy fog developing is on
webcams over the lake north of Evanston, with reduced visibility
being observed in Waukegan as low as 1 mile. For now it was
decided to leave any mention of fog out of the forecast,
except along the northern Illinois shore and nearshore waters.

As an upper level ridge sits over the desert southwest, a weak
upper level trough sits over the Dakotas with RAP analysis
projecting it to sink down the Upper Mississippi River Valley
today. Surface high pressure over the Great Lakes will weaken
through the day today as it slowly moves toward upstate New
York. As mid level winds turn to the southeast, additional
moisture from the Gulf and the Atlantic will be drawn into the
region raising dew points back into the lower 60s. A small vort
max, currently over southern Indiana where there are ongoing
showers, is projected to move northwestward through central
Illinois and into the southern forecast area this afternoon. A
weak inversion and subsidence aloft lowers confidence in both
coverage and whether or not any thunder will develop out of it.
Isolated to scattered showers and possibly some storms are
possible mainly for areas near and south of a Streator to
Fowler line. While there may be some lingering showers after
sunset, confidence is low at this time in them continuing into
the night as they lose diurnal heating.

On Tuesday, the upper level trough over the corn belt is
expected to slide eastward. With better moisture being advected
into the area from the south, better coverage of showers and
storms south of I-80 is expected in the afternoon. There is
lower confidence in how far north the showers and storms
develop, but its not unreasonable that they may push northward
and develop along a lake breeze. Thursday through Saturday look
drier at the moment.

Heat and humidity is expected to steadily increase through the
course of the week. Temperatures are expected to climb into the
low 90s by the end of the week with the potential of near 100
heat indices on Saturday. Heat index values look to remain below
any heat product threshold at the moment and no temperature
records are expected - just a warm up back to summertime vibes.
A cold front is expected to move toward the area by Sunday which
will help cool temps off a bit and bring another chance for
showers and storms, but confidence remains low on the
details/timing due to model uncertainty.

DK

&&

.AVIATION /06Z TAFS THROUGH 12Z TUESDAY/...
Issued at 1245 AM CDT Mon Aug 4 2025

- Patchy VSBY reductions in haze/smoke overnight (mainly VFR)

Sporadic visibility reductions to 5-6 SM will remain possible
overnight before residual low-level smoke lifts north of the
area later in the morning.

Otherwise VFR conditions are expected through the TAF period
with scattered to broken high clouds drifting overhead at times
paired with a layer of higher level smoke aloft. A few VFR
diurnal cumulus may also develop, though the better coverage is
expected south of I-80 and the terminals where even a few spotty
showers can`t be ruled out.

Winds will gradually become light and variable the rest of the
night before returning to a prevailing easterly direction
around 5-10 kts after sunrise. Winds then turn light and
variable again late tonight through early Tuesday morning.

Petr

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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