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.
Every event with a place to put it; 1 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.
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.
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 the western Chicago suburbs and rapidly developed into a line of severe storms extending over the rest of the metro area. The line of storms rapidly moved eastward into northwestern Indiana. These storms left a path of wind damage over southern and southeastern 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 up to 1 inch diameter hail as well.
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, 1:52 PM CST, 2 hours 33 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO IL 252 PM CDT WED JUL 21 2004 .DISCUSSION... CONVECTION HAVING A TOUGH TIME THIS AFTERNOON AND 18Z DVN SOUNDING SHOWS WHY WITH RATHER STRONG CAP AT 850MB. DEWPOINTS REACHING INTO THE UPPER 70S ACROSS THE SOUTHERN HALF OF THE FA WITH EVEN 80 ACROSS CENTRAL IL. DESPITE RATHER THICK CLOUD COVER...EXPECTATIONS IS THAT THUNDERSTORMS WILL FIRE ACROSS SOUTHERN WI/NW IL AND MOVE EAST ACROSS NORTHERN IL INTO NORTHWEST IN. NEW WW JUST ISSUED AND WILL MAINTAIN LIKELY POPS WITH HEAVY RAIN/DAMAGING WIND WORDING FOR THIS EVENING...THEN DRY THINGS OUT ACROSS THE NORTH OVERNIGHT. SLOWER MOVEMENT OF THE FRONT WORKING OUT WELL AND WILL MAINTAIN CHANCE POPS THURS AND THURS EVENING ACROSS THE ENTIRE AREA THEN JUST THE SOUTHERN PART OF THE FA FRIDAY MORNING. TEMPS TODAY INFLUENCED BY MORNING CONVECTION AND CLOUD COVER. EXPECTING LESS CLOUD COVER ON THURS AND WILL STAY WITH GUIDANCE HIGHS PUSHING NEAR 90. MUCH COOLER BEHIND THE FRONT WITH ONLY LOW TO MID 70S FOR HIGHS FRI AND SAT. HIGH PRESSURE MOVES EAST SUNDAY INTO MONDAY HELPING TO MODERATE TEMPS SOME. NO MAJOR CHANGES BEYOND SATURDAY. && .AVIATION DISCUSSION REGARDING 18Z TAFS... WITH ONLY LINGERING SHOWERS REMAINING IN NERN IL TAFS START OUT DRY. ATMOSPHERE REMAINED PRIMED FOR ANOTHER ROUND OF TSTMS THIS AFTERNOON BUT TIMING IS THE QUESTION. BEST CHANCES SEEM TO BE LATER THIS AFTERNOON AND INTO EVENING HOURS. COOL FRONT TO DROP ACROSS AREA AFTER MIDNIGHT WITH WINDS VEERING TO WEST. TRUE FRONT ARRIVES THURSDAY AS WINDS SWING AROUND TO NORTHWEST. && .LOT...WATCHES/WARNINGS/ADVISORIES... .IL...NONE. .IN...NONE. .LK MI...NONE.
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE CHICAGO IL 330 PM 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- 330 PM CDT WED JUL 21 2004 THIS PORTION OF THE HAZARDOUS WEATHER OUTLOOK IS FOR NORTH CENTRAL AND NORTHEAST ILLINOIS...AND NORTHWEST INDIANA. .DAY ONE... TONIGHT THERE IS A MODERATE RISK FOR SEVERE WEATHER THIS EVENING. THE THREAT OF SEVERE WEATHER IS EXPECTED TO END BY 9 PM ACROSS NORTHERN ILLINOIS AND BY 10 PM ACROSS NORTHWEST INDIANA. THE MAIN SEVERE WEATHER THREAT WILL BE DAMAGING WINDS AND HEAVY RAIN. .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. THUNDERSTORMS ARE EXPECTED TO CONTINUE INTO THURSDAY NIGHT. SOME OF THESE STORMS MAY BE SEVERE. THERE IS A CHANCE OF THUNDERSTORMS FRIDAY MORNING SOUTH OF THE KANKAKEE RIVER. .SPOTTER INFORMATION STATEMENT... SPOTTERS WILL BE NEEDED THIS EVENING. && 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- 330 PM CDT WED JUL 21 2004 THIS PORTION OF THE HAZARDOUS WEATHER OUTLOOK IS FOR THE ILLINOIS AND INDIANA WATERS OF LAKE MICHIGAN. .DAY ONE... TONIGHT THERE IS A MODERATE RISK FOR SEVERE WEATHER ACROSS SOUTHERN LAKE MICHIGAN BEFORE 10 PM CDT. THE MAIN SEVERE WEATHER THREAT WILL BE DAMAGING WINDS. .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. THUNDERSTORMS ARE EXPECTED TO CONTINUE INTO THURSDAY NIGHT. SOME OF THESE STORMS MAY BE SEVERE. && COMPLETE FORECAST INFORMATION IS AVAILABLE ON THE NWS CHICAGO WEBPAGE: WWW.CRH.NOAA.GOV/LOT (LOWER CASE)
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO IL
448 PM CDT WED JUL 21 2004
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION...ST.. ...SOURCE....
..REMARKS..
0442 PM TSTM WND DMG WILLOWBROOK 41.76N 87.95W
07/21/2004 DUPAGE IL AMATEUR RADIO
ESTIMATED WIND GUSTS TO 65-70 MPH. LARGE TREE LIMBS DOWN.
REPORTED NEAR INTERSTATE 55 AND ROUTE 83.
&&PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO IL
454 PM CDT WED JUL 21 2004
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION...ST.. ...SOURCE....
..REMARKS..
0427 PM HAIL ROMEOVILLE 41.65N 88.09W
07/21/2004 0.75 INCH WILL IL EMERGENCY MNGR
0425 PM FLOOD AURORA 41.77N 88.29W
07/21/2004 KANE IL TRAINED SPOTTER
MINOR STREET FLOODING.
&&PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO IL
503 PM CDT WED JUL 21 2004
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION...ST.. ...SOURCE....
..REMARKS..
0458 PM TSTM WND DMG CHICAGO RIDGE 41.70N 87.78W
07/21/2004 COOK IL EMERGENCY MNGR
TREE LIMBS DOWN.
0501 PM NON-TSTM WND DMG BRIDGEVIEW 41.74N 87.81W
07/21/2004 COOK IL AMATEUR RADIO
SEVEN INCH DIAMETER TREE SNAPPED IN HALF AT 87TH AND
ROBERTS.
&&PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO IL
508 PM CDT WED JUL 21 2004
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION...ST.. ...SOURCE....
..REMARKS..
0505 PM NON-TSTM WND GST CHICAGO 41.88N 87.63W
07/21/2004 70 MPH COOK IL PUBLIC
MEASURED AT 64TH AND MAPLEWOOD ON THE SOUTH SIDE OF
CHICAGO.
&&PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO IL
512 PM CDT WED JUL 21 2004
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION...ST.. ...SOURCE....
..REMARKS..
0500 PM TSTM WND DMG ALSIP 41.67N 87.74W
07/21/2004 COOK IL LAW ENFORCEMENT
LARGE LIMBS AND SEVERAL TREES AND FLAGPOLES DOWN. WINDS
ESTIMATED TO BER 70 MPH.
&&PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO IL
524 PM CDT WED JUL 21 2004
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION...ST.. ...SOURCE....
..REMARKS..
0514 PM NON-TSTM WND GST GARY 41.60N 87.34W
07/21/2004 60 MPH LAKE IN SHIP
PEAK WIND OF 52 KNOTS MEASURED AT TRUMP CASINO IN
BUFFINGTON HARBOR.
&&The Chicago radar (KLOT), 61 km away, was scanning. The volume nearest the first event began at 22:27 UTC.
7 thunderstorm wind, 2 hail, 1 flash flood. Local standard time, as filed.
Street flooding up to the curbs with portions of 45th St. impassible.
Trees, limbs and power lines were reported down.
A 20 foot tree was knocked down and blocked a road at the Indiana Dunes National Seashore.
Tree limbs and power lines were knocked down.
Trees were down on State Road 10, near Lake Village.
Trees were damaged and a traffic light was broken on Rt. 30.
Trees were knocked down on 114th St.
Numerous trees were reported to be knocked down.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Indiana in 2004Every state in 2004This day in weather historyWarnings in Indiana, July 2004
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: 5414273, 5414274, 5414275, 5414276, 5414277, 5414278, 5414279, 5414280, 5414281, 5414282.