Hail and Damaging Winds in Illinois, July 21, 2004

Name: Hail and Damaging Winds in Illinois, July 21, 2004
Start: 2004-07-21T08:50
End: 2004-07-21T16:01
Location: Illinois

July 21, 2004 · NWS LOT · 18 events in 6 counties and zones

Where it happened

Every event with a place to put it. Tap one for its entry below.

Tornadoes
Tropical storms and surge
Floods
Wind
Hail
Winter weather
Heat and drought
Cold
Fire, smoke and dust
Marine and coastal
Other

Open the live radar over this ground

The toll

Deaths: 0
Injuries: 0
Property damage: None recorded
Crop damage: None recorded
Events: 18

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.

During the morning hours of July 21, a cold front extended from northcentral Wisconsin southwestward through northwestern Iowa. Ahead of the cold front, over the upper midwest, a very humid, unstable airmass had set up. By late morning, a small cluster of thunderstorms had developed over northwestern Illinois. These storms tracked into northcental Illinois, reaching their peak intensity over Ogle County, producing wind gusts up to 58 mph and causing isolated incidents of damage to trees. This storm cluster then weakend as it moved eastward.By early afternoon, more thunderstorms began to develop over northeastern Illinois. A small area of strong thunderstorms initially developed over Kane and western Will Counties and rapidly developed into a line of severe storms extending over the Chicago metro area. The line of storms rapidly moved through Du Page, Cook and Will Counties and into northwestern Indiana. These storms left a path of wind damage over southern portions of the Chicago metro area and into rural sections of northwestern Indiana. Strong wind gusts were also measured by coastal observing stations of Lake Michigan. Numerous incidents of wind damage were observed, with a considerable number of trees knocked down or large limbs torn from trees. Power poles were knocked down over many locations. While the primary threat was strong winds, there were also isolated reports of penny to nickel sized hail as well.

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 Jul 21, 4:45 AM CST, 4 hours 5 minutes earlier.

Area forecast discussion, Jul 21, 4:45 AM CST, 4 hours 5 minutes before

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO IL
545 AM CDT WED JUL 21 2004

.DISCUSSION...
FEW CHANGES WERE MADE TO THE INHERITED FCST AND WILL KEEP THIS
AFD BRIEF. INCREASED POPS FOR TODAY TO LIKELY AND CARRIED INTO
THE EVENING ACROSS THE SRN ZONES. ALSO INSERTED SVR WORDING
FOR TODAY. EARLY SPC DAY-1 ISSUANCE APPEARS TO REFLECT THE
UPCOMING DAY VERY WELL SO WILL NOT ENTIRELY REHASH THAT HERE.
WILL ONLY ADD THAT THE SVR CONCERNS FOR TODAY WILL BE HAIL...
WIND AND LOCALLY HEAVY RAIN AS THE G-R SMOTION OF THE TS WILL BE
SLOW UNTIL SUB-CLOUD LAYER COLD POOL GENERATION INDUCES AN
ACCELERATION ON THE FWD PROPAGATION. CONCERNING HIGH TEMPS...MAV
CONTINUES 90+ TREND WHILE THE ETA IS COOLER ASSOCIATED WITH TS
ACTIVITY. WILL STAY BELOW MAV BUT MAINTAIN HIGHS AT 90 WITH
CONTINUED 70+ DEWS. THEREFORE HEAT INDICES WILL REMAIN BELOW
CRITICAL THRESHOLDS.

MORE TSRA ON THR INTO THR NIGHT AHEAD OF A COLD FRONT. THE FRONT
SHOULD ENTER INTO THE NRN PORTION OF THE CWA LATE THR AFTERNOON
OR THR EVENING CLEARING THE CWA THAT NIGHT. A RELATIVELY COOL AND
DRY CONDITIONS APPEAR IN STORE FOR THE WEEKEND AND INTO NEXT
WEEK.

&&

.AVIATION DISCUSSION REGARDING 12Z TAFS...

AGAIN...PROSPECT FOR SEVERE STORMS THREATENS. TIMING IS THE
QUESTION. THUS WILL HAVE TO LEAVE THEM OUT OF TAFS...BUT WUD EXPECT
THEM TO BLOW UP INTO NRN IL/NWRN INDY THIS AFTN SOMETIME INTO THIS
EVENING. OTHERWISE WILL HAVE BKN AC WITH SOME SCT TO BKN AFTN CU
ARND 4K. SOME LIGHT FOG THIS AM AT RFD AND PSBLY AT DPA...CLEARING
TO AOA 6 MI BY 8AM. WINDS SOUTHWEST TODAY PICKING UP TO 10-15 KTS
AFTER NOON TIL SUNSET. MAY BE A LAKE BREEZE MOVING INLAND FOR A FEW
MILES NOT UNLIKE YDA. THIS BREEZE WITH WIND SHIFT TO EAST WAS NOT
REFLECTED AT TERMINALS YDA AND WILL NOT INPUT A SHIFT TO THE EAST
THIS AFTN EITHER. COOL FNT DROPPING DOWN TO NRN IL AFT MDNGT TONIGHT
SWITCHING WINDS TO WESTNORTHWEST. REAL COLDER AIR WILL BE DELAYED
UNTIL LATE THURSDAY WITH THREAT OF TSTMS REDEVELOPING THURSDAY AS
SECONDARY FNT NEARS.

RLB
&&

.LOT...WATCHES/WARNINGS/ADVISORIES...
.IL...NONE.
.IN...NONE.
.LK MI...NONE.

Hazardous weather outlook, Jul 21, 3:00 AM CST, 5 hours 50 minutes before

HAZARDOUS WEATHER OUTLOOK...CORRECTED
NATIONAL WEATHER SERVICE CHICAGO IL
400 AM CDT WED JUL 21 2004

ILZ003>006-008-010>014-019>022-023-032-033-039-INZ001-002-010-011-019-221100-
WINNEBAGO-BOONE-MCHENRY-LAKE IL-OGLE-LEE-DE KALB-KANE-DU PAGE-COOK-
LA SALLE-KENDALL-GRUNDY-WILL-KANKAKEE-LIVINGSTON-IROQUOIS-FORD-
LAKE IN-PORTER-NEWTON-JASPER-BENTON-
400 AM CDT WED JUL 21 2004

THIS PORTION OF THE HAZARDOUS WEATHER OUTLOOK IS FOR NORTH CENTRAL
AND NORTHEAST ILLINOIS...AND NORTHWEST INDIANA.

.DAY ONE... TODAY AND TONIGHT

SEVERE THUNDERSTORMS ARE LIKELY TODAY AND THIS EVENING. A LARGE COMPLEX OF
THUNDERSTORMS WILL MOVE EAST OUT OF NORTHEAST IOWA INTO NORTHERN ILLINOIS LATER
THIS MORNING. FOR NORTHERN ILLINOIS...THE LEADING EDGE OF THE COMPLEX WILL BE
CAPABLE OF PRODUCING DAMAGING WINDS AND LOCALLY LARGE RAINFALL AMOUNTS...
PRIMARILY NORTH OF INTERSTATE 80. AS THE COMPLEX MOVES EAST INTO NORTHEAST
ILLINOIS IT WILL PRODUCE AN OUTFLOW BOUNDARY. THIS BOUNDARY WILL SERVE AS A
FOCUS FOR RENEWED THUNDERSTORM DEVELOP INTO THE AFTERNOON...PRIMARILY ALONG AND
SOUTH OF INTERSTATE 88. LARGE HAIL..LOCALLY LARGE RAINFALL AMOUNTS AND DAMAGING
WINDS WILL BE THE MAIN CONCERNS. THE AFTERNOON ACTIVITY SHOULD TAPER OFF FROM
WEST TO EAST THIS EVENING.

IN NORTHWEST INDIANA THE THUNDERSTORM COMPLEX SHOULD NOT ARRIVE UNTIL LATE
MORNING OR EARLY AFTERNOON. THE LATER ARRIVAL WILL ALLOW FOR ADDITIONAL DAYTIME
HEATING WHICH WILL ENHANCE ATMOSPHERIC DESTABILIZATION. THE ADDED INSTABILITY
WILL CONTRIBUTE TO A VERY LARGE HAIL AND DAMAGING WIND THREAT. LOCALLY LARGE
RAINFALL AMOUNTS ARE ALSO ANTICIPATED.

.DAYS TWO THROUGH SEVEN... THURSDAY THROUGH TUESDAY

THURSDAY AFTERNOON SHOULD SEE MORE THUNDERSTORMS AHEAD OF A COLD FRONT
THAT WILL ARRIVE IN THE REGION THURSDAY EVENING. AFTER THURSDAY...THE
REGION SHOULD REMAIN DRY AND RELATIVELY COOL THROUGH THE WEEKEND AND
INTO EARLY NEXT WEEK.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL LIKELY BE NEEDED LATER TODAY AND TONIGHT.

&&

COMPLETE FORECAST INFORMATION IS AVAILABLE ON THE
NWS CHICAGO WEBPAGE: WWW.CRH.NOAA.GOV/LOT (LOWER CASE)

LMZ740>746-766-221100-
WINTHROP HARBOR IL TO NEW BUFFALO MI-
LAKE MICHIGAN-
400 AM CDT WED JUL 21 2004

THIS PORTION OF THE HAZARDOUS WEATHER OUTLOOK IS FOR THE ILLINOIS
AND INDIANA WATERS OF LAKE MICHIGAN.

.DAY ONE... TODAY AND TONIGHT

PERIODS OF THUNDERSTORMS ARE EXPECTED LATER TODAY AND INTO THE EVENING.
LOCALLY VERY HEAVY RAINFALL RATES...FREQUENT CLOUD TO GROUND LIGHTING...HAIL
AND GUSTY WINDS ARE POSSIBLE THE STORMS.

.DAYS TWO THROUGH SEVEN... THURSDAY THROUGH TUESDAY

THURSDAY AFTERNOON SHOULD SEE MORE THUNDERSTORMS AHEAD OF A COLD FRONT
THAT WILL ARRIVE IN THE REGION THURSDAY EVENING. AFTER THURSDAY...THE
REGION SHOULD REMAIN DRY AND RELATIVELY COOL THROUGH THE WEEKEND AND
INTO EARLY NEXT WEEK.

&&

COMPLETE FORECAST INFORMATION IS AVAILABLE ON THE
NWS CHICAGO WEBPAGE: WWW.CRH.NOAA.GOV/LOT (LOWER CASE)

The radar

The Chicago radar (KLOT), 103 km away, was scanning. The volume nearest the first event began at 14:50 UTC.

Open the radar archive at this moment

Event by event

14 thunderstorm wind, 4 hail. Local standard time, as filed.

Thunderstorm Wind, Ogle

When: July 21, 8:50 AM CST
Where: Ogle County, Chana
Measured: 50 kt (58 mph) estimated gust
Reported by: GENERAL PUBLIC
Coordinates: 41.983, -89.217

Trees knocked down by strong wind gusts.

Thunderstorm Wind, Ogle

When: July 21, 9:00 AM CST
Where: Ogle County, Kings
Measured: 50 kt (58 mph) estimated gust
Reported by: GENERAL PUBLIC
Coordinates: 42.000, -89.100

Large limbs torn off of trees.

Thunderstorm Wind, Ogle

When: July 21, 9:00 AM CST
Where: Ogle County, Rochelle
Measured: 50 kt (58 mph) estimated gust
Reported by: LAW ENFORCEMENT
Coordinates: 41.917, -89.067

Large limbs torn off of trees.

Hail, Kane

When: July 21, 3:00 PM CST to 3:05 PM CST
Where: Kane County, Montgomery
Measured: 0.88 in hail
Reported by: EMERGENCY MANAGER
Coordinates: 41.733, -88.350

The hail was reported at the intersection of Rt. 30 and Rt. 31.

Thunderstorm Wind, Will

When: July 21, 3:15 PM CST to 3:20 PM CST
Where: Will County, 2 mi W of Bolingbrook
Measured: 50 kt (58 mph) estimated gust
Reported by: TRAINED SPOTTER
Coordinates: 41.667, -88.167

Tree limbs were reported down at the intersection of Boughton Rd. and Weber Rd and trees were knocked down at the intersection of Royce Rd. and Concord Rd.

Thunderstorm Wind, Will

When: July 21, 3:18 PM CST
Where: Will County, Plainfield
Measured: 50 kt (58 mph) estimated gust
Reported by: EMERGENCY MANAGER
Coordinates: 41.600, -88.200

A tree fell on to a power line.

Thunderstorm Wind, Du Page

When: July 21, 3:20 PM CST to 3:30 PM CST
Where: Du Page County, Naperville
Measured: 60 kt (69 mph) estimated gust
Reported by: AMATEUR RADIO
Coordinates: 41.783, -88.150

A 24 inch diameter tree was knocked down and a 12 inch branch was torn from a tree.

Hail, Kendall

When: July 21, 3:25 PM CST to 3:30 PM CST
Where: Kendall County, 3 mi E of Yorkville
Measured: 0.75 in hail
Reported by: TRAINED SPOTTER
Coordinates: 41.633, -88.400

Hail, Will

When: July 21, 3:26 PM CST to 3:31 PM CST
Where: Will County, Romeoville
Measured: 0.88 in hail
Reported by: EMERGENCY MANAGER
Coordinates: 41.633, -88.067

The hail was observed Interstate 55 and Budler Rd.

Thunderstorm Wind, Du Page

When: July 21, 3:33 PM CST
Where: Du Page County, Woodridge
Measured: 50 kt (58 mph) estimated gust
Reported by: EMERGENCY MANAGER
Coordinates: 41.733, -88.033

Tree limbs were down at the intersection of Rt. 53 and 75th St.

Thunderstorm Wind, Cook

When: July 21, 3:35 PM CST
Where: Cook County, Lemont
Measured: 55 kt (63 mph) estimated gust
Reported by: AMATEUR RADIO
Coordinates: 41.667, -88.000

Trees were knocked down on Main St. between Cortland Rd. and Rt. 83.

Thunderstorm Wind, Du Page

When: July 21, 3:42 PM CST
Where: Du Page County, Willowbrook
Measured: 60 kt (69 mph) estimated gust
Reported by: AMATEUR RADIO
Coordinates: 41.750, -87.967

Large tree limbs were reported down near Interstate 55 and Rt. 83.

Hail, Cook

When: July 21, 3:55 PM CST to 4:00 PM CST
Where: Cook County, Chicago
Measured: 0.75 in hail
Reported by: TRAINED SPOTTER
Coordinates: 41.833, -87.650

Large hail was reported near the intersection of 64th St. and Maple Ave.

Thunderstorm Wind, Cook

When: July 21, 3:58 PM CST
Where: Cook County, Chicago Hgts
Measured: 50 kt (58 mph) estimated gust
Reported by: EMERGENCY MANAGER
Coordinates: 41.500, -87.633

Large tree limbs were reported down.

Thunderstorm Wind, Cook

When: July 21, 4:00 PM CST
Where: Cook County, Chicago Lawn
Measured: 60 kt (69 mph) estimated gust
Reported by: TRAINED SPOTTER
Coordinates: 41.783, -87.700

Large tree limbs were down near 64th St. and Maple Ave.

Thunderstorm Wind, Cook

When: July 21, 4:00 PM CST
Where: Cook County, Alsip
Measured: 60 kt (69 mph) estimated gust
Reported by: LAW ENFORCEMENT
Coordinates: 41.667, -87.733

Large limbs, several trees and flag poles were knocked down.

Thunderstorm Wind, Cook

When: July 21, 4:00 PM CST
Where: Cook County, Burbank
Measured: 60 kt (69 mph) estimated gust
Reported by: TRAINED SPOTTER
Coordinates: 41.733, -87.767

Large tree limbs, trees, power line and power poles were knocked down.

Thunderstorm Wind, Cook

When: July 21, 4:01 PM CST
Where: Cook County, Bridgeview
Measured: 60 kt (69 mph) estimated gust
Reported by: AMATEUR RADIO
Coordinates: 41.750, -87.800

A 7 inch diameter tree was snapped in half at 87th St. and Roberts Rd.

What these are

Thunderstorm Wind: Winds from a thunderstorm of 50 knots (58 mph) or more, or lower winds that caused damage or casualties. Measured gusts are marked MG, estimated EG.
Hail: Hail three-quarters of an inch or larger, or smaller hail that caused damage, filed with the largest stone measured.

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

The same day elsewhere

Every storm in Illinois in 2004 Every state in 2004 This day in weather history Warnings in Illinois, July 2004

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: 5412323, 5412324, 5412325, 5412326, 5412327, 5412328, 5412329, 5412330, 5412331, 5412332, 5412333, 5412334, 5414267, 5414268, 5414269, 5414270, 5414271, 5414272.