708
FXUS63 KLOT 182328
AFDLOT

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

.KEY MESSAGES...

- Scattered thunderstorms ending this evening across the
  southern cwa.

- 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 /00Z TAFS THROUGH 06Z MONDAY/...
Issued at 628 PM CDT Sat Jul 18 2026

The only forecast concern this period is the return of wildfire
smoke and associated cigs/vis.

An enhanced lake breeze/cold front is moving west across
northeast IL early this evening, shifting winds to the northeast.
Speeds in the 10-15kt range will slowly diminish through the mid
evening hours and some gusts into the 15-20kt range are possible
for the next few hours. Speeds will gradually diminish under
10kts overnight and then increase back toward 10kt again Sunday.

The northeast winds are spreading wildfire smoke back into the
area and the limited available guidance for smoke movement
shows the wildfire smoke continuing to thicken this evening and
especially overnight into early Sunday morning. While confidence
is low, opted to go with prevailing 2sm during the overnight
hours for the Chicago terminals and then lift vis back into mvfr
Sunday morning. There is some potential for vis to improve back
to vfr later Sunday afternoon into Sunday evening. If the vis
does drop into the 2sm range, there may be a similar cig
response as there was a few days ago, with mvfr cigs possible.
Opted to included scattered mention for now. cms

&&

.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 through Sunday morning for ILZ006-
     ILZ103-ILZ104.

IN...Beach Hazards Statement 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 until 4 AM CDT Sunday for the IL and IN
     nearshore waters.

&&

$$

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