Tornadoes and Flash Flood in Illinois, June 11, 2026

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1250 PM CDT Thu Jun 11 2026

.KEY MESSAGES...

- Another round or two of severe storms are expected today with
  the period of greatest threat between 4 and 11 PM. All
  hazards (tornadoes, destructive winds, destructive hail) are
  possible across the entire area.

- In particular, there is a threat for strong to intense
  tornadoes this evening (4 to 8 PM) especially along and north
  of Interstate 88.

- After a dry and cooler day on Friday, there is another threat
  for severe weather on Saturday.

&&

.MESOSCALE...
Issued at 1146 AM CDT Thu Jun 11 2026

Complex and somewhat low confidence forecast this afternoon and
evening, but despite the uncertainties in the evolution, we're
still quite concerned about a potential significant severe
weather outbreak, including the potential for strong tornadoes.

Late this morning, regional WSR-88D mosaic shows a well defined
MCV lifting northeast into southwest WI. Weakening bow echo to
the south of this MCV is moving into our western CWA at this
time, but encountering a more stable low and mid level air mass
and generally weakening. In the short term, weakening of this
convection associated with the powerful overnight bow echo is
likely to continue. Air to the east of this line is beginning to
recover over northeast IL, but it isn't clear if gradual
destabilization will take place quickly enough for this bow echo
to reintensify before reaching Lake Michigan early this
afternoon. We are starting to see some reintensification both
on satellite and radar with and some deeper cores along the
southern portion of the line. This is currently focused across
the I-39 corridor and latitudinally between I-88 and I-80, and
then extending southwestward from there. Thus we will need to
watch the I-80 corridor into Grundy, Kendall, and Will counties
over the coming hours where an axis of higher mid level lapse
rates exists.

The area where these storms are reinvigorating is the area
we're growing more concerned with is to the south of the cold
pool footprint left by this lead MCS, which looks to set up over
southern portions of our CWA or northern portions of ILX's CWA.
Ahead of this, yesterday's outflow boundary which had stalled
near the I-70 corridor overnight is quickly mixing out and low
level moisture is rapidly advecting northward. Dewpoints have
been quickly jumping from the mid- upper 60s into the low- mid
70s across central IL and up to the Kankakee and Illinois River
Valleys. Temperatures have also quickly warmed into the lower
80s and should continue to slowly warm despite the blow off high
cloudiness from the MCS. Modifying ILX's morning sounding for
83/73 yields SBCAPE over 3000 J/kg with minimal inhibition.

There seems to be a play for the convection over extreme NE MO
and extreme southeast IA to move into this quickly destabilizing
air mass and become rooted in the boundary layer and quickly
strengthen in a couple of hours. Meanwhile, the kinematic field
across this area is progged to quickly improve between 19z and
22z with 925mb progged to increase from 15kt to over 30kt and
850mb flow from 20kt to over 40kt. The result will be low level
hodographs becoming large and sickle shaped with significant
streamwise vorticity. Any discrete cells moving into this
environment will likely become supercells given the strong and
strengthening deep layer shear, but with low LCLs and the
forecast evolution of the hodographs, there would be a potential
for strong to intense tornadoes. It is important to stress that
these storms over NE MO are not well handled by CAM guidance
and will be divorced from the stronger forcing, leading to
greater uncertainty regarding their future existence, let alone
intensity. However, given recent observational trends this is
something we will be monitoring closely in the near few hours.

Farther west, strong sfc low for this time of year is lifting
northeastward into IA. Evidence of the strong synoptic forcing is
evident with considerable elevated convection developing over
eastern IA overtop of the cold pool from this morning's MCS. This
convection is likely to reinforce the cold pool in the short term.
However, as the sfc low continues northward, the strong
isallobaric response should result in strengthening southerly
winds and composite outflow and warm front lifting northward and
developing warm sector in advance of the cold front.

CAM guidance remains very aggressive with a strongly unstable and
rather large warm/unstable sector ahead of the cold front, though
most CAMs do not seem to be handling the current size/magnitude
of the MCS and associated cold pool well. Recent observational
trends raise significant questions about how realistic the CAM
depictions are. Certainly, given the magnitude of the forcing, we
feel that at least some moderate destabilization will occur and
likely support a strongly forced QLCS developing along the cold
front this afternoon and spreading into northern IL this evening.
Magnitude of the recovery and subsequent destabilization across
northern IL is somewhat unclear ahead of this QLCS, but given the
strong forcing and unseasonably strong deep and low level shear,
there could a damaging wind and QLCS tornado threat even with
somewhat modest instability. Should recovery and instability be
more significant, like many CAMS show, then potential would
increase for a derecho/QLCS tornado threat this evening. We will
be closely monitoring observational trends this afternoon.

- Izzi

&&

.DISCUSSION...
Issued at 304 AM CDT Thu Jun 11 2026

     THREAT FOR STRONG TORNADOES AND DESTRUCTIVE WINDS IN THE
REGION THIS AFTERNOON AND EVENING...

Early morning water vapor imagery depicts broad aggregate
upper-level troughing centered on the northern Plains. Several
embedded short-wavelength troughs are parading around the
perimeter of the broader trough, including a notable impulse
moving across central Wyoming at press time. Per recent
mesoanalysis data across the central Plains, the impulse has
already led to the development of a lee cyclone centered in
western Kansas. Meanwhile, a broad region of warming cloud tops
extends across the Lower Great Lakes associated with a
gradually-decaying mesoscale convective system. Per a recent
surface analysis, outflow from the convective system has
(temporarily) displaced a warm frontal zone southward, with the
boundary currently stretching from central Indiana through
south-central Illinois and northeastern Missouri. Between both
large-scale features, convection is developing across southern
Nebraska associated with presumably a mid-level gravity wave
originating from unbalanced upper-level flow (a notable 75kt jet
streak is departing the base of the aforementioned Wyoming
shortwave). Indeed, am noting the hallmarks of developing
gravity wave associated convection (GWAC) along the I-80
corridor in Nebraska at press time.

As the Wyoming shortwave ejects east-northeastward into the
Great Lakes this morning, the southern Plains low will rapidly
shift northeastward from near Kansas City, Missouri toward
central Iowa. Ahead of the surface low, the developing
convection in southern Nebraska is expected to intensify and
consolidate into a compact mesoscale convective system or GWAC
supercell complex and track east-northeastward toward the
Mississippi River and eventually into northern Illinois. It is
unclear if the convection would ultimately become surface-based
as the boundary layer warms and synoptic warm front retreats
northward (more on this soon), though the presence of steep mid-
level lapse rates (contributing to MUCAPE > 2000 J/kg) and
increasing shear profiles (effective shear in excess of 50 kt)
will support a threat for destructive winds (>70 mph) and hail
(>2" in diameter) with the first round of storms. The time
window for the early-day storms looks to be generally between 11
AM and 3 PM, mainly north of Interstate 80. (Am somewhat
skeptical of CAM guidance depicting early-afternoon convection
decaying while approaching Lake Michigan).

Later this afternoon and evening, ensemble model guidance
remains in agreement that the surface low will deepen toward the
lower to mid 990s mb range while lifting into central
Wisconsin. Intensifying south to southwesterly flow on the
southeastern side of the surface low will lead to rapid airmass
recovery across northern Illinois as well as the advection of an
EML plume back into the Lower Great Lakes. CAM-based guidance
suggests that dew points in the warm sector will soar into the
mid to locally upper 70s this afternoon, apparently a
consequence of evaporation of water from the heavy rain
yesterday evening and early this morning to our south and west.
Resulting mean 1km mixing ratios nearing 19 g/kg and mid-level lapse
rates of around 8 K/km will contribute to MLCAPE of locally 3500
J/kg in the warm sector. At the same time, low- to upper-level flow
will rapidly intensify across the warm sector during the afternoon
and evening leading to strong deep-layer shear profiles.

Thunderstorms appear poised to develop across central Iowa by
mid-afternoon and then expand in coverage and increase in
intensity while moving toward northern Illinois and southern
Wisconsin this evening and eventually northwestern Indiana after
sunset. Given the degree of strong forcing, strong instability,
and high moisture values, a somewhat messy storm mode is
expected with a mix of high-precipitation supercells and line
clusters eventually merging into a squall line with a threat
for all hazards (tornadoes, destructive winds, and wind-blown
damaging hail). The main time window for severe weather this
evening appears to be from 4 to 11 PM.

Am quite concerned in a relatively narrow west-to-east zone
favorable for strong to intense tornadoes (EF-3+) somewhere
across southern Wisconsin or northern Illinois particularly
between 4 and 8 PM. Forecast soundings along the warm front this
evening depict a rare and volatile combination of exceptional
instability augmented by locally pooled moisture (MLCAPE >4000 J/kg)
and intense low-level shear (350 J/kg of 0-1km SRH for eastward-
moving storms, nearly all of characterized by streamwise horizontal
vorticity), leading to effective STP values in the double-digits.
Pinpointing the eventual location of the warm front will be
paramount to identifying the zone of greatest tornado potential
today with reasonable outcomes ranging from the front stalling near
Interstate 88 in northern Illinois to the I-94 corridor in southern
Wisconsin (consensus is near the Wisconsin state line). Such a
threat for strong to intense tornadoes is contingent on a supercell
storm mode being maintained, though the degree of low-level shear
would still support strong QLCS tornadoes near the warm front.

Just want to conclude by saying that environments supportive of
strong to intense tornadoes often have many off-ramps and are
accordingly never a guarantee. Will the warm front surge
well north of our area taking the primary tornado threat with it?
Will the morning storms suppress the warm front south, or not allow
for rapid destabilization ahead of the cold front? Will storm mode
remain far too messy to sustain strong low- level rotation and
tornadoes? Or, will there be a discrete supercell that latches onto
the warm front draped across our area? These factors are essentially
noise within the broader signal to craft a forecast and can only be
determine as an event is unfolding (sometimes literally just an hour
or two beforehand). Taken altogether, today is a day to stay very
connected to the forecast and to ensure you have multiple ways to
get warning information for the off chance that the dominoes do end
up falling in the wrong direction in our area.

Friday onward:

A brief break in the pattern is expected on Friday with
noticeably lower humidity values and temperatures. Broad upper-
level cyclonic flow will remain across the northern United
States through the weekend and beyond, maintaining periodic
opportunities for showers and thunderstorms. Will note another
threat for severe weather on Saturday as a more notable
shortwave and associated cold front moves into the Great Lakes
and interacts with a narrow EML plume and low- level moisture
return. At first glance, the main threats on Saturday should be
damaging hail and damaging winds.

Borchardt

&&

.AVIATION /18Z TAFS THROUGH 00Z SATURDAY/...
Issued at 1250 PM CDT Thu Jun 11 2026

Key messages for the 18Z TAF period:

* Showers and non-severe thunderstorms to begin the period with
  gusty westerly winds possible

* Additional strong to severe thunderstorms in the mid-afternoon
  to early evening. Strong to damaging wind gusts, hail, and
  LIFR vsbys will be possible

The period opens up with a push of showers and non-severe
thunderstorms moving east across the Chicago metro. Gusty W
winds to around 30 kt and pockets of moderate to heavy rain can
be expected through around 19Z with additional showers
lingering. Storms have moved past RFD at the time of this
writing and will see largely shower activity through mid-
afternoon.

A push of strong to severe thunderstorms will roll across N IL
from the west from mid-afternoon through early evening. Storms
look to approach RFD after 21Z and the Chicago sites after 23Z.
Widespread strong to damaging wind gusts are the primary concern
from a TAF perspective, although instances of severe hail and
tornadoes will also be possible with these storms. Heavy to
torrential rainfall should bring vsbys down to at least IFR with
LIFR likely for a brief period. The severe threat should last
on the order of an hour or less over any given location with
additional showers and storms trailing into the mid-evening.

Outside of thunderstorm winds, WSW winds will back around to
SSE for mid-afternoon behind this first push of storms. Winds
will then abruptly turn westerly with the arrival of the
stronger storms and remain westerly into Friday. Gusts to 20 to
25 kt following the storms will persist into the night.

Doom

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Flood Watch until 11 PM CDT this evening for ILZ003-ILZ004-
     ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ019-
     ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ103-ILZ104-
     ILZ105-ILZ106-ILZ107-ILZ108.

IN...Flood Watch until 11 PM CDT /midnight EDT/ this evening for
     INZ001-INZ002-INZ010-INZ011-INZ019.

LM...Small Craft Advisory from 4 PM this afternoon to 10 PM CDT
     this evening for the IL and IN nearshore waters.

&&

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Hazardous Weather Outlook
National Weather Service Chicago/Romeoville IL
1129 AM CDT Thu Jun 11 2026

ILZ003>006-008-010>013-019>021-023-032-033-039-103>108-INZ001-002-
010-011-019-121630-
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-
1129 AM CDT Thu Jun 11 2026 /1229 PM EDT Thu Jun 11 2026/

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

.DAY ONE...This Afternoon and Tonight.

Weather hazards expected...

  Elevated Thunderstorm Risk...with an associated:
     Level 4 of 5 Damaging Wind Risk...up to 80 mph.
     Level 3 of 5 Tornado Risk.
     Level 2 of 5 Isolated Large Hail Risk...up to 2 inches in diameter.
  Elevated Flooding Risk.

DISCUSSION...

Following a round of early afternoon storms, a second wave of
of more substantial storms will develop in advance of an
approaching cold front this afternoon. These storms are expected
to move across the area between 4 and 10 PM. These storms will be
capable of producing tornadoes and destructive winds, some
possibly significant. Instances of flash flooding may also occur
where thunderstorms repeatedly hit the same area.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

Saturday...
  Limited Thunderstorm Risk...with an associated:
     Level 1 of 5 Severe Thunderstorm Risk.
  Limited Flooding Risk.

Sunday through Wednesday...
  Limited Thunderstorm Risk.

.SPOTTER INFORMATION STATEMENT...

  Spotters will be needed today.

GENERAL STORM MOTION OF THE DAY:

  Moving toward the east at around 45 mph.

LMZ740>745-121630-
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-
1129 AM CDT Thu Jun 11 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...This Afternoon and Tonight.

Weather hazards expected...

  Hazardous conditions for small craft.
  Significant Thunderstorm Risk...with an associated:
     Thunderstorm Waterspout Risk
     Level 4 of 5 Thunderstorm Wind Gust Risk...up to 65 knots.
     Level 2 of 5 Hail Risk...up to 1 inch in diameter.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

Saturday...
  Limited Thunderstorm Risk...with an associated:
     Level 1 of 5 Severe Thunderstorm Risk.
Sunday through Wednesday...
  Limited Thunderstorm Risk.

KJB

Visit us at www.weather.gov/chicago

Preliminary Local Storm Report
National Weather Service Chicago IL
1208 PM CDT Thu Jun 11 2026

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

0334 PM     Tstm Wnd Dmg     2 E Shorewood           41.52N 88.16W
06/10/2026                   Will               IL   Public

            Multiple photos shared via social media show
            large branches broken at and near Inwood
            Golf Course. Time estimated by radar.

&&

WSL

Preliminary Local Storm Report
National Weather Service Chicago IL
1212 PM CDT Thu Jun 11 2026

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

0357 PM     Tstm Wnd Dmg     Stickney                41.82N 87.78W
06/10/2026                   Cook               IL   Broadcast Media

            Roofing material peeled from an apartment
            building near Pershing Road and Ridgeland
            Avenue in Stickney. Time estimated by radar.

&&

WSL

Preliminary Local Storm Report
National Weather Service Chicago IL
1217 PM CDT Thu Jun 11 2026

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

0313 PM     Tstm Wnd Dmg     5 SW Morris             41.30N 88.50W
06/10/2026                   Grundy             IL   Emergency Mngr

            Grundy County EMA reports multiple power
            poles snapped along Verona Road just south
            of DuPont Road. Time estimated by radar.

&&

WSL

Preliminary Local Storm Report
National Weather Service Chicago IL
1243 PM CDT Thu Jun 11 2026

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

0334 PM     Tstm Wnd Dmg     3 N Plainfield          41.65N 88.20W
06/10/2026                   Will               IL   Public

            Multiple tree branches broken in northern
            Plainfield. Relayed via broadcast media.
            Time estimated by radar.

&&

WSL

Preliminary Local Storm Report
National Weather Service Chicago IL
1244 PM CDT Thu Jun 11 2026

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

1215 PM     Flood            3 NNE Buckley           40.64N 88.02W
06/11/2026                   Iroquois           IL   Broadcast Media

            Video shows US-45 flooded with a few inches
            of standing water north of 1000 North Road
            from nearby creek. Relayed via broadcast
            media.

&&

WSL

Preliminary Local Storm Report
National Weather Service Chicago IL
1256 PM CDT Thu Jun 11 2026

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

0407 PM     Tstm Wnd Dmg     South Shore - Chicago   41.76N 87.58W
06/10/2026                   Cook               IL   Public

            Multiple public reports of tree branches
            broken in South Shore community area of
            Chicago. Relayed by Chicago 311. Time
            estimated by radar.

0405 PM     Tstm Wnd Dmg     Lincoln Square - Chicag 41.97N 87.69W
06/10/2026                   Cook               IL   Public

            Multiple public reports of tree branches
            broken in Lincoln Square, Uptown, and
            Edgewater community areas of Chicago.
            Relayed by Chicago 311. Time estimated by
            radar.

0403 PM     Tstm Wnd Dmg     1 E Auburn-Gresham      41.74N 87.65W
06/10/2026                   Cook               IL   Public

            Multiple public reports of tree branches
            broken in Auburn Gresham community area of
            Chicago. Relayed by Chicago 311. Time
            estimated by radar.

0401 PM     Tstm Wnd Dmg     Morgan Park - Chicago   41.69N 87.67W
06/10/2026                   Cook               IL   Public

            Multiple public reports of tree branches
            broken in Morgan Park community area of
            Chicago. Relayed by Chicago 311. Time
            estimated by radar.

0401 PM     Tstm Wnd Dmg     1 SSW Washington Hts -  41.71N 87.65W
06/10/2026                   Cook               IL   Public

            Multiple public reports of tree branches
            broken in Washington Heights community area
            of Chicago. Relayed by Chicago 311. Time
            estimated by radar.

0308 PM     Tstm Wnd Dmg     Portage Park - Chicago  41.96N 87.77W
06/10/2026                   Cook               IL   Public

            Multiple public reports of tree branches
            broken in Portage Park community area of
            Chicago. Relayed by Chicago 311. Time
            estimated by radar.

&&