Excessive Heat and Heat in Illinois, June 29 to 30, 2026

Name: Excessive Heat and Heat in Illinois, June 29 to 30, 2026
Start: 2026-06-29T11:00
End: 2026-06-30T23:59
Location: Illinois

June 29 to 30, 2026 · NWS LOT · 22 events in 22 counties and zones

Hot and humid conditions developed across northern Illinois on June 29th and continued on June 30th as well into early July. Peak heat index values ranged from 100 to 105 for most areas on both days with high temperatures in the lower to middle 90s.

Where it happened

Every event with a place to put it; 22 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.

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The toll

Deaths: 0
Injuries: 0
Property damage: None recorded
Crop damage: None recorded
Events: 22

Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.

What happened

The episode as NWS LOT wrote it up.

What forecasters said that day

The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS Chicago, IL wrote its last area forecast discussion before the first event at Jun 29, 5:21 AM CST, 5 hours 39 minutes earlier. Its key messages:

Dangerous heat is expected across the area this week with afternoon heat index values forecasted over 100 degrees. Little to no relief is expected at the lakeshore or at night.
A return to a more active pattern and thunderstorm chances is likely by the weekend.

Area forecast discussion, Jun 29, 5:21 AM CST, 5 hours 39 minutes before

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
621 AM CDT Mon Jun 29 2026

.KEY MESSAGES...

- Dangerous heat is expected across the area this week with
  afternoon heat index values forecasted over 100 degrees.
  Little to no relief is expected at the lakeshore or at night.

- A return to a more active pattern and thunderstorm chances is
  likely by the weekend.

&&

.DISCUSSION...
Issued at 159 AM CDT Mon Jun 29 2026

No changes made to ongoing heat headlines, with an Extreme Heat
Warning for Cook County and a Heat Advisory for all other
counties running from noon today through 10 PM CDT Wednesday
evening.

Evening upper air analysis depicts an unseasonably deep long-
wave upper trough and embedded closed low over the western
CONUS, and downstream upper ridging from the lower Mississippi
Valley into the Midwest. At the surface, deep low pressure
around 996 mb was over northeast Colorado, with a warm front
arcing into northwest IA and then southeast along roughly a
KMLI-KCMI-KHUF line across central Illinois and southwest
Indiana as of midnight. This warm front is expected to lift
north across the WFO LOT forecast area this morning, as the
low develops north-northeastward across the Plains in response
to a strong mid-level short wave rounding the base of the
aforementioned upper low in the west.

Meanwhile, the upper ridge is progged to build north-northeast
into the Ohio Valley today through Wednesday, strengthening to
nearly 6000 meters. Model 850 mb temperatures of +20/22C today
and +23/25C across the forecast area Tuesday and Wednesday will
support unseasonably warm surface temperatures in the lower and
middle 90s (perhaps a few upper 90s in spots), as well as
relatively strong capping with 700 mb temperatures +12C or
higher. Despite the strength of this capping inversion, breezy
southwest low-level flow and dry air aloft is likely to aid in
mixing out dew points during the warmest parts of each day, with
guidance generally indicating mid-70s afternoon Td values
(slightly lower across the urbanized Chicago metro area).
Forecast peak heat indices therefore remain around 105 or just a
bit higher for the most part.

With the relatively warm mid-level temperatures and associated
capping, the main axis of thunderstorm potential today through
Wednesday is expected to remain northwest of the forecast area
across parts of IA/MN and WI. Some guidance does indicate that
convective complexes will occur to our northwest both tonight
and Tuesday night, which could push decaying convection, or more
likely, associated outflow boundaries into northern IL during
the early parts of both Tuesday and Wednesday. While these
outflows could potentially impact heat indices and would need to
be monitored, the breezy southwest flow across the region would
most likely mix out the effects on surface temps/dew points
during the day.

By Thursday and Friday, the center of the upper ridge is
forecast to shift slightly southeast across Kentucky and
Tennessee, flattening across the upper Midwest and Great Lakes
regions as the western CONUS upper low lifts out across Ontario.
Cooler mid-level temps result in weaker capping across the
upper Midwest, and increase the likelihood of thunderstorm
complexes (or their remains) working into the forecast area at
times. While still warm and muggy even into next weekend, peak
daytime heat indices are forecast more in the 90s to around 100
degree range even without accounting for direct impacts of
storms or convective outflows. Thus the timing of current heat
headlines, which run through Wednesday evening, continues to
look very reasonable. In fact, over the weekend, current
guidance and ensembles eventually flatten/break down the ridge
over the southeastern U.S., and indicate a return to a
potentially more active (storm-wise), zonal jet pattern.

Ratzer

&&

.AVIATION /12Z TAFS THROUGH 18Z TUESDAY/...
Issued at 621 AM CDT Mon Jun 29 2026

Though MVFR conditions are favored through the period, the
combination of low-level moisture advecting northward and onset
of daytime heating is allowing patches of high-end IFR to low-
end MVFR stratus to develop. Expectation is for these clouds to
quickly lift through the morning, but a couple periods of BKN
MVFR ceilings cannot be ruled out through mid-morning.

SSW/SW winds are expected through the period, with gusts to 20
knots this morning and around 25 knots this afternoon. Though
surface winds will diminish after sunset, a 40 to 45 knot low-
level jet brushing northern Illinois to the north will either
produce sporadic surface gusts to around 20 knots or lead to
LLWS. Expectation is that some gusts will persist at ORD/MDW due
to weaker near surface stability over the urban heat island.
However, have included LLWS at RFD and DPA as gusts will likely
end late this evening and overnight.

Kluber

&&

.CLIMATE...
Issued at 252 AM CDT Sun Jun 28 2026

     .Daily Records for the Upcoming Week........

Chicago (KORD)
            Record High       Record Warm Minimum
June 29       97 (1954)            80 (1931)
June 30       99 (1953)            80 (2018)
July 1       103 (1956)            78 (1931)
July 2        99 (1970)            79 (1911)
July 3       102 (1949)            78 (1911)
July 4       102 (2012)            80 (1921)

Rockford (KRFD)
            Record High       Record Warm Minimum
June 29      103 (1931)            75 (1931)
June 30      102 (1931)            76 (2018)
July 1       101 (1931)            76 (1970)
July 2        99 (1910)            74 (1970)
July 3        99 (1925)            75 (2012)
July 4       102 (2012)            77 (1977)

NWS Chicago

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Heat Advisory from noon today to 10 PM CDT Wednesday for
     ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-
     ILZ013-ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-
     ILZ106-ILZ107-ILZ108.

     Extreme Heat Warning from noon today to 10 PM CDT Wednesday
     for ILZ103-ILZ104-ILZ105.

IN...Heat Advisory from noon CDT /1 PM EDT/ today to 10 PM CDT /11
    PM EDT/ Wednesday for INZ001-INZ002-INZ010-INZ011-INZ019.

LM...Small Craft Advisory from noon today to 10 PM CDT this evening
     for the IL nearshore waters.

&&

Visit us at weather.gov/chicago

Hazardous weather outlook, Jun 29, 2:15 AM CST, 8 hours 45 minutes before

Hazardous Weather Outlook
National Weather Service Chicago/Romeoville IL
315 AM CDT Mon Jun 29 2026

ILZ003>006-008-010>013-019>021-023-032-033-039-103>108-INZ001-002-
010-011-019-300815-
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-
315 AM CDT Mon Jun 29 2026 /415 AM EDT Mon Jun 29 2026/

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

.DAY ONE...Today and Tonight.

Weather hazards expected...

  Elevated Excessive Heat Risk.

DISCUSSION...

Dangerous heat with afternoon heat index values over 100 degrees
is expected today. Heat index values will remain above 75 in most
areas tonight, offering little relief from the heat.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

Tuesday and Wednesday...
  Elevated Excessive Heat Risk.
Thursday...
  Limited Flooding Risk.
  Limited Thunderstorm Risk.
  Elevated Excessive Heat Risk.
Friday...
  Limited Flooding Risk.
  Limited Thunderstorm Risk.
Saturday and Sunday...
  Limited Thunderstorm Risk.

DISCUSSION...

Dangerous heat with afternoon heat index values over 100 degrees
is expected to persist through at least Wednesday. Depending on
potential thunderstorm coverage late in the week, the dangerous
heat may persist into the weekend. It does appear that a more
active pattern will return by the weekend, with a return of
more frequent thunderstorm chances.

.SPOTTER INFORMATION STATEMENT...

  Spotter activation will not be necessary through tonight.

LMZ740>745-300815-
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-
315 AM CDT Mon Jun 29 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...Today and Tonight.

  Hazardous conditions for small craft are likely.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

Tuesday...
  Hazardous conditions for small craft are likely.
Thursday through Sunday...
  Limited Thunderstorm Risk.

Ratzer

Visit us at www.weather.gov/chicago

The radar

The national radar mosaic for the moment the first event began.

Open the radar archive at this moment

Event by event

19 heat, 3 excessive heat. Local standard time, as filed.

Heat, Winnebago

When: June 29, 11:00 AM CST to June 30, 11:59 PM CST
Where: Winnebago forecast zone
Reported by: ASOS
Coordinates: 42.336, -89.161 (the zone’s center; the record gives no point)

Heat, Boone

When: June 29, 11:00 AM CST to June 30, 11:59 PM CST
Where: Boone forecast zone
Reported by: ASOS
Coordinates: 42.323, -88.823 (the zone’s center; the record gives no point)

Heat, McHenry

When: June 29, 11:00 AM CST to June 30, 11:59 PM CST
Where: McHenry forecast zone
Reported by: ASOS
Coordinates: 42.324, -88.452 (the zone’s center; the record gives no point)

Heat, Lake

When: June 29, 11:00 AM CST to June 30, 11:59 PM CST
Where: Lake forecast zone
Reported by: ASOS
Coordinates: 42.349, -87.862 (the zone’s center; the record gives no point)

Heat, Ogle

When: June 29, 11:00 AM CST to June 30, 11:59 PM CST
Where: Ogle forecast zone
Reported by: AWOS
Coordinates: 42.043, -89.321 (the zone’s center; the record gives no point)

Heat, Lee

When: June 29, 11:00 AM CST to June 30, 11:59 PM CST
Where: Lee forecast zone
Reported by: AWOS
Coordinates: 41.746, -89.300 (the zone’s center; the record gives no point)

Heat, Kane

When: June 29, 11:00 AM CST to June 30, 11:59 PM CST
Where: Kane forecast zone
Reported by: ASOS
Coordinates: 41.939, -88.429 (the zone’s center; the record gives no point)

Heat, De Kalb

When: June 29, 11:00 AM CST to June 30, 11:59 PM CST
Where: De Kalb forecast zone
Reported by: AWOS
Coordinates: 41.894, -88.770 (the zone’s center; the record gives no point)

Heat, Du Page

When: June 29, 11:00 AM CST to June 30, 11:59 PM CST
Where: Du Page forecast zone
Reported by: ASOS
Coordinates: 41.852, -88.086 (the zone’s center; the record gives no point)

Heat, La Salle

When: June 29, 11:00 AM CST to June 30, 11:59 PM CST
Where: La Salle forecast zone
Reported by: AWOS
Coordinates: 41.344, -88.886 (the zone’s center; the record gives no point)

Heat, Kendall

When: June 29, 11:00 AM CST to June 30, 11:59 PM CST
Where: Kendall forecast zone
Reported by: ASOS
Coordinates: 41.591, -88.429 (the zone’s center; the record gives no point)

Heat, Grundy

When: June 29, 11:00 AM CST to June 30, 11:59 PM CST
Where: Grundy forecast zone
Reported by: AWOS
Coordinates: 41.285, -88.418 (the zone’s center; the record gives no point)

Heat, Northern Will County

When: June 29, 11:00 AM CST to June 30, 11:59 PM CST
Where: Northern Will County forecast zone
Reported by: AWOS
Coordinates: 41.445, -87.979 (the zone’s center; the record gives no point)

Heat, Southern Will County

When: June 29, 11:00 AM CST to June 30, 11:59 PM CST
Where: Southern Will County forecast zone
Reported by: AWOS
Coordinates: 41.445, -87.979 (the zone’s center; the record gives no point)

Heat, Eastern Will County

When: June 29, 11:00 AM CST to June 30, 11:59 PM CST
Where: Eastern Will County forecast zone
Reported by: AWOS
Coordinates: 41.445, -87.979 (the zone’s center; the record gives no point)

Heat, Livingston

When: June 29, 11:00 AM CST to June 30, 11:59 PM CST
Where: Livingston forecast zone
Reported by: AWOS
Coordinates: 40.892, -88.558 (the zone’s center; the record gives no point)

Heat, Kankakee

When: June 29, 11:00 AM CST to June 30, 11:59 PM CST
Where: Kankakee forecast zone
Reported by: AWOS
Coordinates: 41.138, -87.862 (the zone’s center; the record gives no point)

Heat, Ford

When: June 29, 11:00 AM CST to June 30, 11:59 PM CST
Where: Ford forecast zone
Reported by: AWOS
Coordinates: 40.597, -88.223 (the zone’s center; the record gives no point)

Heat, Iroquois

When: June 29, 11:00 AM CST to June 30, 11:59 PM CST
Where: Iroquois forecast zone
Reported by: AWOS
Coordinates: 40.747, -87.824 (the zone’s center; the record gives no point)

Excessive Heat, Northern Cook County

When: June 29, 11:00 AM CST to June 30, 11:59 PM CST
Where: Northern Cook County forecast zone
Reported by: ASOS
Coordinates: 41.895, -87.646 (the zone’s center; the record gives no point)

Excessive Heat, Central Cook County

When: June 29, 11:00 AM CST to June 30, 11:59 PM CST
Where: Central Cook County forecast zone
Reported by: ASOS
Coordinates: 41.895, -87.646 (the zone’s center; the record gives no point)

Excessive Heat, Southern Cook County

When: June 29, 11:00 AM CST to June 30, 11:59 PM CST
Where: Southern Cook County forecast zone
Reported by: AWOS
Coordinates: 41.895, -87.646 (the zone’s center; the record gives no point)

What these are

Heat: Heat below excessive heat criteria that still caused deaths, injuries or significant impacts.
Excessive Heat: Heat at or above the local excessive heat warning criteria, or heat that caused deaths.

After NWS Directive 10-1605, the rules offices file Storm Data by.

The same day elsewhere

Every storm in Illinois in 2026 Every state in 2026 This day in weather history Warnings in Illinois, June 2026

Sources

NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 1351137, 1351138, 1351139, 1351140, 1351141, 1351142, 1351143, 1351144, 1351145, 1351147, 1351148, 1351149, 1351151, 1351152, 1351153, 1351158, 1351161, 1351162, 1351164, 1351193, 1351194, 1351196.