141
FXUS63 KLOT 272329
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
629 PM CDT Mon Jul 27 2026

.KEY MESSAGES...

- Scattered strong, locally severe thunderstorms early this
  evening southeast cwa, then a chance of showers and possibly a
  thunderstorm mid/late evening ahead of the cold front.

- Dangerous heat and humidity early this evening near/west I-39.

- Dangerous swimming conditions due to large waves and strong
  currents expected through Wednesday morning.

&&

.DISCUSSION...
Issued at 208 PM CDT Mon Jul 27 2026

Early this afternoon, a broken line of severe convection with
embedded supercells is tracking east across the interior Chicago
metro area. Since the start of the afternoon, these storms have
likely been responsible for at least one tornado, if not a few,
large hail, and some road flooding. Latest SPC mesoanalysis
suggests up to 5,000 J/kg of MLCAPE resides over NE IL which
have been allowing for convective cloud tops up -80C reaching
heights over 60,000 ft. This cluster had developed along a tight
instability gradient on the leading edge of a low level
shortwave disturbance pushing across northern IL. The system as
a whole is being carried toward the east with the synoptic wave
while individual cells are tracking more southeastward with a NW
shear profile. With activity beginning to cross into
northwestern IN as of 1PM, would imagine these storms should
have little to no trouble maintaining themselves over the next
couple of hours as they spread SE over our IN counties. All
hazards will remain possible with these storms into late
afternoon before moving away to our east including damaging to
destructive winds, large hail, flooding, and possibly a tornado.


Depending on how long these current storms and isolated trailing
activity want to fester in our eastern CWA, we may see a brief
relative lull in activity during the mid-late afternoon.
Thereafter, additional thunderstorms may target our area along
and ahead of a cold front during the late afternoon and evening.
Severe storms associated with this feature are already ongoing
over east-central WI. Guidance has been of little help today
going back and forth with solutions for later today. This
morning, camps were backing off on additional convection this
evening, but latest CAM guidance is starting to get excited
again. It`s not entirely clear to what extent the ongoing
convection will influence the low level thermodynamic
environment for later. Outflow from ongoing storms is pushing
away from the metro into the outlying areas. Wouldn`t imagine at
this point in the day that the unstable airmass will have time
to recover much where its been removed. Nonetheless, the
environment aloft will remain plenty unstable and supportive of
additional severe storms later if parcels can be sufficiently
forced. However, forcing along the front appears rather meager
with not a ton of help from features aloft. Additionally, lots
of deep layer dry advection, including through the low levels,
will take place on the back edge of the shortwave between now
and this evening. This will work against deep convective
development down into northern IL this evening along the front.
With this sort of instability though and with storms already
ongoing, imagine it`s rather likely we see at least some
activity during the evening hours; whether it`s severe remains
unclear. The highest coverage during the evening is heavily
favored across the eastern half of the CWA near and east of the
track of the disorganized surface low. If storms can mature
along the front later today, damaging winds will be the biggest
concern with hail and flooding also a possibility. Little to no
low level instability and unfavorable hodographs don`t appear to
present much of a tornado threat this evening, even with
surface-based storms.

Storms should move away from the area by the end of the
evening. Gusty northerly winds will develop in the wake of the
front late tonight into tomorrow, especially over the lake. This
will quickly generate high waves and dangerous currents on the
lake and a High Swim Risk is forecast at area Lake Michigan
beaches from late tonight into Wednesday morning. Some patches
of fog may also attempt to develop in the wake of the front late
tonight, but not seeing much of a signal for any widespread
dense fog. Rather, we may be stuck beneath a blanket of gloomy
low stratus during the morning tomorrow.

The cold frontal passage will bring relatively cooler (albeit
still warm) conditions to the middle of the week with lower and
middle 80s forecast Tuesday and Wednesday afternoons. Regional
high pressure will bring quiet and largely sunny conditions to
the middle part of the week before another synoptic system looks
to bring more rain and storm chances to the region by Friday.

Doom

&&

.AVIATION /00Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 629 PM CDT Mon Jul 27 2026

Forecast concerns include...

Chance of showers early this evening.
Gusty south/southeast winds this evening.
Wind shift/cold front to northeast overnight.
Low mvfr/ifr cigs overnight/Tuesday morning.

Current thunderstorm activity is south of the terminals and
moving south and away from the terminals. A cold front over
southern WI will move across the area this evening with a chance
of showers and possibly an isolated thunderstorm. Added prob
shower mention for this potential.

Current south/southeast winds gusting into the lower/mid 20kt
range will diminish over the next few hours, shift westerly
later this evening, then northwesterly behind the cold front.
Winds will then shift to the north/northeast during the early
overnight hours when gusts to 20kt will be possible. North/
northeast winds will continue for the rest of the period with
gusts into the lower/mid 20kt range through sunset Tuesday
evening when speeds/gusts will diminish.

There is currently few/sct low mvfr level cloud cover near Lake
Michigan and this is not expected to become a prevailing cig
this evening. Prevailing low mvfr cigs are expected overnight
into Tuesday morning with ifr cigs are also possible. Have opted
for only tempo ifr mention for now and trends will need to be
monitored. Cigs will lift and scatter by mid/late morning. cms

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Extreme Heat Warning until 9 PM CDT this evening for ILZ003-
     ILZ004-ILZ008-ILZ010-ILZ011-ILZ019-ILZ032.

     Beach Hazards Statement through Wednesday morning for ILZ006-
     ILZ103-ILZ104.

IN...Beach Hazards Statement through Wednesday morning for INZ001-
     INZ002.

LM...Small Craft Advisory from 1 AM Tuesday to 7 AM CDT Wednesday
     for the IL and IN nearshore waters.

&&

$$

Visit us at weather.gov/chicago