Flash Flood and Flooding in Indiana, June 17, 2026

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
211 PM CDT Wed Jun 17 2026

.KEY MESSAGES...

- An outbreak of severe thunderstorms is expected across the
  region this afternoon and evening. Storms, those well south
  of I-80 (particularly south of the Kankakee River), will have
  the potential to produce damaging tornadoes, destructive
  straight line winds, and large hail.

- A flood watch remains in effect. Locally heavy rainfall is
  expected to result in an enhanced threat of localized flash
  flooding.

- Tranquil weather is expected to close out the work week in the
  wake of this system.

- Another strong storm system is expected to bring a return of
  showers and thunderstorms later this weekend, with some
  potential for heavy rainfall and/or severe weather somewhere
  in the general region.

&&

.DISCUSSION...
Issued at 211 PM CDT Wed Jun 17 2026

Early this afternoon, we find a widespread mess of showers and
a few embedded thunderstorms falling on the area east of a
double-barreled surface low centered over IA and MN. These
showers have been riding along the MUCAPE gradient as it
spread east across northern IL on the nose of the low level
warm conveyor. A surface warm front is extending across central
IL south of the CWA with higher thunder coverage near and south
of the front into the instability reservoir. The front continues
to sharpen up with time as strong theta-e advection hits it
from south. A lack of elevated instability extending north of
the front owing to poor lapse rates aloft accounts for the lack
of thunder coverage into northern IL. Nonetheless, strong
kinematic and low level upglide in a moisture-rich environment
allowed for widespread moderate to heavy rainfall across
northern IL through much of the morning. A wake low also
developed north of I-80 behind the departing heavier rain.
Strong southeast winds with gusts periodically over 50 mph
prompted us to issue a Wind Advisory for our northern CWA, but
they continue to gradually ease from west to east.

Still a somewhat tricky setup for this afternoon with
unresolvable mesoscale uncertainties looming through the next
several hours. The warm front, while sharpening with time, has
made little to no headway north or southward through about 1
PM. All eyes will be on the evolution of this boundary over the
next several hours as it will dictate the northern extent of the
much higher severe threat, including the appreciable tornado
and destructive wind threat, as additional storms are slated to
develop along and ahead of the approaching cold front. We're
already seeing some pre-frontal development over SE IA which
could evolve into severe convection in the near term, especially
cells that stay along and south of the warm front. Latest CAM
guidance favors this front inching just northward into mid-
afternoon and opening up the far southern CWA to this higher
severe threat. However, enough of a signal remains to be
ignored, including a consistent one from the RAP, for the front
to surge farther north, possibly closer to I-80. At this time,
this does not look very likely, aside from perhaps a brief
window toward the late afternoon/early evening as the low center
works across and perhaps brings a brief window of ML instability
farther north later today.

The more impressive kinematic field will be found out ahead of
the front this afternoon. In fact, SPC mesoanalysis paints eye-
catching long, looping hodographs over northern and central IL
at the moment, we just don't have the instability to make any
good use of that right now. Meanwhile, hodos straighten out
upstream toward the Mississippi thanks to a veering, weakening
low level wind field closer to the cold front. Any convection
that can initiate ahead of the front, such as along the pre-
frontal trough axis, will be exposed to a much more concerning
shear profile than activity along the front itself. Storms
currently developing over SE IA fit this mark and will need to
be watched closely as they progress across IL.

Put together, the threat for strong tornadoes and destructive
wind gusts is still alive and well, but now may be confined to
only the far southern portions of our CWA through the
afternoon. Namely, areas south of the Kankakee River are most
favored to reside along/south of the warm front and offer the
highest ceiling for severe weather over the next few to several
hours. Quickly stabilizing conditions should put a halt on the
tornado threat and highest wind threat north of the front, but
damaging winds will certainly be possible across northern IL
with elevated convection through the afternoon. The main window
for the severe potential in our CWA will be roughly 3 PM through
6 PM with additional, likely non-severe storms possible through
mid-evening along the cold front.

Additionally, the moisture-rich environment with PWATs just
under 2" across northern IL will lead to torrential rainfall in
thunderstorms and a threat for flash flooding. Strong dynamic
and kinetic forcing and efficient upglide along the elevated
face of the warm front will spread the heavy rain and flooding
threat north of the surface front. Guidance is consistent in
resolving over a widespread 1 inch+ of rain with areas of
higher totals very attainable. The highest QPF is favored near
and south of I-80. A Flood Watch is currently in effect outside
of our northern-most counties.

Gusty gradient winds will develop tonight behind the departing
low with wind 25 to 30 mph wind gusts forecasts for much of the
night. After this evening, rain-free conditions are forecast
into the weekend. Cooler-than-normal temperatures will begin
trending warmer over the coming days with lower 70s forecast
tomorrow with upper 70s/near 80 again by Saturday. Another
synoptic system is progged to move across the region in the
Sunday to Monday period. Previously, had been looking like
another decent opportunity for heavy rain and severe weather,
although latest medium range guidance has been trending south of
the area. Look for a more detailed analysis of this system in
future discussions once today is behind us.

Doom

&&

.AVIATION /18Z TAFS THROUGH 00Z FRIDAY/...
Issued at 1244 PM CDT Wed Jun 17 2026

Key Messages:

- Strong SE winds lingering through about 19z near MDW/GYY

- Showers and embedded thunderstorms expanding in coverage
  across the Chicago-area terminals this afternoon.

- SW wind shift this afternoon and then a NW wind shift
  overnight into Thursday morning.

- Chances for showers/thunderstorms this evening.

- Periods of MVFR cigs through Thursday morning.

A lingering burst of strong southeasterly winds near MDW/GYY
will gradually subside through 19z. The threat for embedded
thunderstorms will then increase after 19-20z. The storm threat
should then shift south of the c90 TRACON by 23-00z. Winds will
then shift out of the southwest and ease late this afternoon.

Later this evening, winds will increase once again and MVFR cigs
are expected to re-develop across the region late tonight into
Thursday morning. There is a small chance for showers and a few
thunderstorms  this evening as a front moves across the region,
but chances remain a bit too low for TEMPO groups. Rough timing
for this would be about 23-01z at RFD and 01-03z at the Chicago-
area sites.

MVFR cigs should lift to VFR through late Thursday morning.

Carlaw

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Beach Hazards Statement through late tonight for ILZ006-ILZ103-
     ILZ104.

     Flood Watch until 9 PM CDT this evening for ILZ006-ILZ012-
     ILZ013-ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-
     ILZ103-ILZ104-ILZ105-ILZ106-ILZ107-ILZ108.

     Flood Watch until 5 PM CDT this afternoon for ILZ008-ILZ010-
     ILZ011.

IN...Flood Watch until 9 PM CDT /10 PM EDT/ this evening for INZ001-
     INZ002-INZ010-INZ011-INZ019.

     Beach Hazards Statement from 1 AM CDT Thursday through
     Thursday afternoon for INZ002.

LM...Gale Warning until 7 PM CDT this evening for the IL and IN
     nearshore waters.

     Small Craft Advisory from 7 PM this evening to 9 AM CDT
     Thursday for the IL and IN nearshore waters.

&&

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Hazardous Weather Outlook
National Weather Service Chicago/Romeoville IL
219 PM CDT Wed Jun 17 2026

ILZ003>006-008-010>013-019>021-023-032-033-039-103>108-INZ001-002-
010-011-019-181930-
Winnebago-Boone-McHenry-Lake IL-Ogle-Lee-De Kalb-Kane-DuPage-
La Salle-Kendall-Grundy-Kankakee-Livingston-Iroquois-Ford-
Northern Cook-Central Cook-Southern Cook-Northern Will-
Southern Will-Eastern Will-Lake IN-Porter-Newton-Jasper-Benton-
219 PM CDT Wed Jun 17 2026 /319 PM EDT Wed Jun 17 2026/

This Hazardous Weather Outlook is for portions of north central
Illinois...northeast Illinois and northwest Indiana.

.DAY ONE...Tonight.

Weather hazards expected...

  Significant Thunderstorm Risk...with an associated:
     Level 3 of 5 Tornado Risk mainly south of the Kankakee River.
     Level 3 of 5 Damaging Wind Risk...up to 65 mph.
     Level 3 of 5 Large Hail Risk...up to half dollar size.
  Significant Flooding Risk mainly near and south of I-80.
  High Swim Risk Illinois Lake Michigan Beaches.

DISCUSSION...

Thunderstorms are expected this afternoon and early evening. The
strongest storms, currently favored south of the Kankakee River,
will be capable of producing large hail, damaging winds, and
potentially strong tornadoes. Farther north, damaging winds will
be the biggest concern with afternoon storms.

Thunderstorms today will also be capable of producing torrential
rainfall which could lead to localized flash flooding and sudden
river/stream rises.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

Thursday...
  High Swim Risk Porter County Lake Michigan Beaches.
Saturday...
  Limited Thunderstorm Risk.
Sunday...
  Limited Flooding Risk.
  Limited Thunderstorm Risk.
Monday and Tuesday...
  Limited Thunderstorm Risk.

.SPOTTER INFORMATION STATEMENT...

  Spotters will likely be needed this afternoon and evening.

GENERAL STORM MOTION OF THE DAY:

  Moving toward the east at 50 to 60 mph.

LMZ740>745-181930-
Winthrop Harbor to Wilmette Harbor IL-
Wilmette Harbor to Northerly Island IL-
Northerly Island to Calumet Harbor IL-
Calumet Harbor IL to Gary IN-Gary to Burns Harbor IN-
Burns Harbor to Michigan City IN-
219 PM CDT Wed Jun 17 2026

This Hazardous Weather Outlook is for portions of the Illinois
nearshore waters of Lake Michigan and the Indiana nearshore
waters of Lake Michigan.

.DAY ONE...Tonight.

Weather hazards expected...

  Gale force winds and or very hazardous waves.
  Significant Thunderstorm Risk...with an associated:
     Thunderstorm Waterspout Risk
     Level 3 of 5 Thunderstorm Wind Gust Risk...up to 50 knots.
     Level 2 of 5 Hail Risk...up to quarter size.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

Thursday morning...
  Hazardous conditions for small craft are likely.
Saturday...
  Limited Thunderstorm Risk.
Sunday...
  Hazardous conditions for small craft are likely.
  Limited Thunderstorm Risk.
Monday...
  Hazardous conditions for small craft are likely.
Tuesday...
  Limited Thunderstorm Risk.

Doom

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Preliminary Local Storm Report
National Weather Service Chicago IL
1222 PM CDT Wed Jun 17 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1155 AM     Non-Tstm Wnd Gst 1 NE Montrose Harbor    41.97N 87.63W
06/17/2026  M54 MPH          LMZ741             IL   C-Man Station

            Measured gust at Montrose Harbor.

&&

ZY

Preliminary Local Storm Report
National Weather Service Chicago IL
1224 PM CDT Wed Jun 17 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1152 AM     Non-Tstm Wnd Gst 8 ENE Montrose Harbor   42.00N 87.50W
06/17/2026  M63 MPH          LMZ779             IL   C-Man Station

            Measured gust at the Harrison-Dever Crib.

&&

ZY

Preliminary Local Storm Report
National Weather Service Chicago IL
1247 PM CDT Wed Jun 17 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1152 AM     Marine Tstm Wind 8 ENE Montrose Harbor   42.00N 87.50W
06/17/2026  M63 MPH          LMZ779             IL   C-Man Station

            Corrects previous non-tstm wnd gst report
            from 8 ENE Montrose Harbor. Measured gust at
            the Harrison-Dever Crib.

&&

ZY

Preliminary Local Storm Report
National Weather Service Chicago IL
1248 PM CDT Wed Jun 17 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1155 AM     Marine Tstm Wind 1 NE Montrose Harbor    41.97N 87.63W
06/17/2026  M54 MPH          LMZ741             IL   C-Man Station

            Corrects previous non-tstm wnd gst report
            from 1 NE Montrose Harbor. Measured gust at
            Montrose Harbor.

&&

ZY

Preliminary Local Storm Report
National Weather Service Chicago IL
1250 PM CDT Wed Jun 17 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1228 PM     Non-Tstm Wnd Gst Midway Airport          41.79N 87.75W
06/17/2026  M59 MPH          Cook               IL   ASOS

            Peak wind gust at KMDW of 59 mph (51 kts).

&&

ZY

Preliminary Local Storm Report
National Weather Service Chicago IL
1252 PM CDT Wed Jun 17 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1226 PM     Non-Tstm Wnd Gst 8 ENE Montrose Harbor   42.00N 87.50W
06/17/2026  M66 MPH          LMZ779             IL   C-Man Station

            New peak wind at the Harrison-Dever Crib.

&&

ZY