640
FXUS63 KLOT 151905
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
205 PM CDT Wed Jul 15 2026

.KEY MESSAGES...

- Hot conditions will continue through the week with high
  temperatures generally in the upper 80s to 90s and overnight
  lows in the 70s.

- A period of reduced visibility due to smoke may occur on
  Thursday generally along and northeast of Interstate 90.

- An isolated storm possible on Thursday, with increasing
  storm chances Friday and then again late Saturday afternoon
  into Saturday evening.

&&

.DISCUSSION...
Issued at 205 PM CDT Wed Jul 15 2026

High pressure continues to reside across the Great Lakes and
Upper Midwest regions which has set up another warm and humid
summer afternoon. Despite the hazy skies aloft and some diurnal
cumulus, temperatures have warmed into the upper 80s and lower
90s thus far and should warm another few degrees before all is
said and done. The exception will be near the lake where a lake
breeze is oozing inland and should keep temperatures a bit
cooler in the mid-80s. Dew points have also been mixing down
once again which is keeping peak indices around 100 degrees
which is solidly below local heat advisory criteria. That said,
with the lack of wind these temperatures will feel oppressive so
be sure to stay hydrated and take frequent breaks if out and
about.

Tonight, temperatures will once again cool into the lower to
mid-70s overnight with light and somewhat variable winds. There
will also be increasing smoke coverage, especially aloft, as the
plume that has been blanketing northern WI and MI drifts
southward. While hi-res guidance continue to depict some surface
smoke concentrations making it into portions of northern IL and
northwest IN, the inland and southward extent of the smoke
remains unclear. That said, any surface smoke would result in
periods of reduced visibility (possibly as low as 2-3 miles) in
addition to poor air quality. Thus, the IL EPA an IDEM has
extended the Air Quality Alerts to include most of our IL and IN
counties (except for Kankakee, Livingston, Ford, Iroquois, and
Benton counties) through Thursday night.

Some concentration of wild fire smoke is expected to persist
through the day on Thursday as north-northeast winds aloft
persist and the high pressure center begins to drift into the
southeastern CONUS. Despite the smoke, temperatures are still
expected to warm into the lower 90s for much of the area.
However, east-northeast winds near the lake will keep
temperatures in the low to mid-80s there. With cooler
temperatures and slightly lower dew points, peak heat indices
will be more in the 95-100 degree range. Furthermore, there also
remains a low (15-20%) chance for some isolated thunderstorms
as the shortwave currently over the southern Mississippi Valley
drifts north. With deep moisture return ahead of the wave
expected to be rather limited, the lingering subsidence from the
high, and recent forecast soundings showing some capping in
place suspect most areas will remain dry.

Heading into Friday, the aforementioned high will be well out
of the area allowing the northwest flow aloft to pivot another
weak shortwave into the Great Lakes in addition to the lingering
wave to our south. The forcing from these two features in
combination with deeper moisture is expected to result in a
broader coverage of scattered showers and thunderstorms on
Friday especially during the afternoon and hours. Given the weak
deep layer shear, thunderstorms on Friday should remain sub-
severe. Though, the humid air mass overhead will allow any
storms to be capable of locally heavy downpours which could
result in ponding issues if storms propagate over the same areas
for extended periods of time. While a brief break in the rain
is expected Friday night into early Saturday, another (and much
deeper) shortwave is expected to dive across the Great Lakes
Saturday afternoon which will result in an additional period of
scattered showers and thunderstorms. Similar to Friday, the
kinematic environment looks rather weak so not expecting much in
the way of severe weather but locally heavy downpours will be
possible.

In the wake of the Saturday wave, high pressure is forecast to
build in for Sunday and result in a period of more tranquil
weather. Temperatures will still be on the seasonably warm side
with highs in the mid to upper 80s, but with winds expected to
be out of the east- northeast cooler conditions are expected
near the lake. Unfortunately the quiet weather doesn`t look to
last long as more shortwaves are progged to pivot through the
region early next week and bring with them additional chances
for showers and thunderstorms. Regardless, temperatures will
remain in the near to above average range with daily highs in
the 80s to lower 90s and overnight lows in the upper 60s to 70s.

Yack

&&

.AVIATION /18Z TAFS THROUGH 00Z FRIDAY/...
Issued at 1255 PM CDT Wed Jul 15 2026

Key aviation forecast messages:

- Potential lake breeze this afternoon at ORD/MDW/GYY

- Low confidence in wind trends on Thursday which may impact
  timing of any VSBY reductions in smoke

West winds around 5-10 kt are ongoing early this afternoon
across the area. We are monitoring the lake breeze yet again
today with continued lower confidence on its inland extent
through early evening. Have maintained the 20Z MDW and 21Z ORD
timing for an east wind shift with this update but it remains
possible that it stalls just east of the terminals again. Winds
then ease with sunset, becoming light and variable through early
Thursday morning. Confidence in prevailing wind directions
during the day on Thursday remains low, however, with guidance
varying from either west southwest to east northeast This would
also have implications regarding the timing of any potential
VSBY reductions associated with the wildfire smoke to our north
which may drift into portions of the area at times on Thursday,
though any potential MVFR/near-IFR VSBYs may not arrive until
late Thursday afternoon/early evening in the wake of a
reinforcing lake breeze.

Petr

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Air Quality Alert until midnight CDT Thursday night for ILZ003-
     ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-
     ILZ019-ILZ020-ILZ021-ILZ103-ILZ104-ILZ105-ILZ106-ILZ107-
     ILZ108.

IN...Air Quality Alert until midnight CDT Thursday night for INZ001-
     INZ002-INZ010-INZ011.

     Air Quality Alert until 1 AM EDT Thursday for INZ019.

LM...None.

&&

$$

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