238
FXUS63 KLOT 181921
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
221 PM CDT Sat Jul 18 2026

.KEY MESSAGES...

- A line of scattered thunderstorms will continue along the
cold front through mid-evening. A few storms could be strong
to severe with damaging winds up to 60 mph.

- Wildfire smoke is expected to move in behind the front this
evening and overnight resulting in reduced visibilities and
poor air quality through at least Sunday.

&&

.DISCUSSION...
Issued at 221 PM CDT Sat Jul 18 2026

A cold front is draped from central Lower MI to east-central IA
and is progressing southward across northern IL and northwest
IN. Scattered thunderstorms have developed along the front,
especially in northwest IN, and that trend is expected to
continue as the front moves through the rest of the area into
this evening. Given the weaker wind shear present (around 25-30
kts) most of these storms are expected to remain sub-sever, but
a few stronger to possibly severe storms cannot be ruled out
particularly for areas south of I- 80 and east of I-57. The cold
front and the associated thunderstorms are expected to exit our
area between 7-8 PM CDT this evening with otherwise dry
conditions expected for the rest of the night.

Behind the front, north-northeast winds will begin to usher in
another plume of wildfire smoke. While the latest smoke guidance
continues to show the concentration to be less than what was
seen the past couple days, upstream observations are showing
visibilities in the 1-3 mile range across northern MI and WI. So
expect the plume of smoke to result in at least some localized
reduced visibilities (most likely in the 2-5 mile range) through
Sunday in addition to poor air quality. In fact, the IL EPA and
IDEM have extended the Air Quality Alerts for our entire
forecast area through Sunday night to account for the forecast
unhealthy air quality. Aside from the smoke and poor air
quality, the weather on Sunday will be otherwise tranquil with
east-northeast winds around 5-10 mph and temperatures in the
lower to mid-80s. Though with the onshore winds highs near the
lake will only be in the mid to upper 70s.

Heading into Monday, a couple of shortwave troughs are forecast
to be ejecting out of the northern Plains and diving across the
Great Lakes. The leading shortwave is expected to move into the
mid- Mississippi Valley early Monday morning and is currently
forecast to have a cluster of thunderstorms associated with it.
Should this storm cluster develop as most guidance (both
deterministic and handful of ensemble members) suggests, it
should traverse across MN and IA before dissipating. In its wake
guidance suggests that the cluster will lay out an outflow
boundary which will serve as the focus for additional showers
and thunderstorms Monday afternoon and evening as the second
shortwave pivots into the area. If the aforementioned track
occurs as forecast then any new storms on Monday should develop
mainly to the west of our area which in turn would give us
another dry afternoon. However, if the cluster either fails to
develop or the outflow is able to drift further east, then a the
favored axis of showers and thunderstorms Monday
afternoon/evening would materialize more into northern IL and
maybe northwest IN. Given the deep layer shear around 30-35 kts,
any storms that develop overhead on Monday could become strong
to possibly severe. While most guidance has trended towards the
western solution, there is still enough guidance members that
show something moving through our area to warrant the
maintenance of the 60-70% POPs offered by the NBM. That said,
the thinking is that these POPs are likely too high and
hopefully we can reduce them in future forecasts if the westward
trend continues.

Regardless of what happens during the day on Monday, it does
seem that a period of scattered showers may develop Monday night
as the shortwave moves through the Great Lakes. By Tuesday any
showers (or storms) should move out of the area as high pressure
is expected to begin building in from the north. This high is
then forecast to persist through much of next week which should
keep any rain chances to a minimum. However, winds next week
look to remain out of the east-northeast for most days which
should keep daily high temperatures in the mid to upper 80s with
overnight lows in the 60s. Unfortunately more rain chances do
look to return heading into next weekend as another series of
shortwaves dives through the region.

Yack

&&

.AVIATION /18Z TAFS THROUGH 00Z MONDAY/...
Issued at 111 PM CDT Sat Jul 18 2026

Key Messages:

- Thunderstorms to depart the vicinity of MDW and GYY by 20Z.

- Northeasterly wind shift expected this afternoon/evening.

- Visibility reductions from smoke likely to return this evening
and continue through tomorrow.


Thunderstorms ongoing near MDW and GYY at press time will
continue in the vicinity of those terminals through 19-20Z.
Couldn`t completely rule out the development of additional
cells along a lake-enhanced front this afternoon, but otherwise,
the convective shower/storm activity should remain south of the
terminals through the remainder of the day today.

The aforementioned front/lake breeze will result in a
northeasterly wind shift at the Chicago metro terminals at some
point this afternoon and an easterly wind shift at RFD this
evening. While winds may become light and variable in some spots
for a time tonight, a northeasterly wind direction will prevail
at the Chicago metro terminals tomorrow, with a more easterly
or east-northeasterly direction favored at RFD.

Smoke originating from wildfires in western Ontario and
northern Minnesota will return to the area this evening and
persist into the daytime tomorrow. High-resolution smoke models
indicate that near-surface smoke concentrations won`t be as
severe as they were here on Thursday and Friday, but visibility
reductions to at least MVFR levels appear likely from the
incoming smoke based on upstream observations.

Ogorek

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Air Quality Alert until midnight CDT Sunday night for ILZ003-
ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-
ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ103-
ILZ104-ILZ105-ILZ106-ILZ107-ILZ108.

Beach Hazards Statement from 7 PM CDT this evening through
Sunday morning for ILZ006-ILZ103-ILZ104.

IN...Beach Hazards Statement from 7 PM CDT this evening through
Sunday morning for INZ001-INZ002.

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

Air Quality Alert from 1 AM Sunday to 1 AM EDT Tuesday for
INZ019.

LM...Small Craft Advisory from 7 PM this evening to 4 AM CDT Sunday
for the IL and IN nearshore waters.

&&

$$

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