155
FXUS63 KLOT 041141
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
641 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 3-5 miles outside of Chicago with reports of either smoke or
haze. As the low-mid level flow turns to the southeast today this
should help lift the greater surface concentrations of smoke
north of the area by mid afternoon. Models are still suggesting
a large plume of smoke lingers over the area today and
potentially into tomorrow, but the expectation is for this to
remain mainly aloft.

Dew point depressions are steadily decreasing this morning.
While patchy shallow fog in rural areas cannot be completely
ruled out, the lowest visibilities have been along the Lake
Michigan shore north of Evanston, with reduced visibility being
observed in Waukegan as low as 1 mile, likely augmented by the
higher near-surface smoke concentrations.

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, IL to
Fowler, IN 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 /12Z TAFS THROUGH 18Z TUESDAY/...
Issued at 641 AM CDT Mon Aug 4 2025

- VSBY reductions in haze/smoke linger this morning, especially
  at RFD/DPA

Visibility reductions to 2-5 SM will remain possible for the
next few hours at RFD and DPA before the residual low-level
smoke layer slowly begins to shift back north of the area. It
is possible TEMPO MVFR VSBYs need to be continued through midday
if it is slower to exit.

Otherwise VFR conditions are expected through the rest of the
TAF period with scattered to broken high clouds drifting
overhead at times paired with a layer of higher level smoke
aloft which will likely stick around into tomorrow. While a
stray shower can`t be fully ruled out overnight into early
Tuesday morning (10% chance), dry conditions are currently
forecast through the period.

Winds will settle into a prevailing easterly direction today
around 8-10 kt through the evening then ease and become light
and variable overnight. Winds then once again return to a
prevailing easterly direction during the day on Wednesday.

Petr

&&

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

&&

$$

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