A large cluster of thunderstorms formed over Upper Michigan during the overnight hours of July 20th, and then made a right turn over northern Lower Michigan during the morning hours of July 21st. This complex slowly weakened as it moved through southeast Michigan.
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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 DTX wrote it up.
A large cluster of thunderstorms formed over Upper Michigan during the overnight hours of July 20th, and then made a right turn over northern Lower Michigan during the morning hours of July 21st. This complex slowly weakened as it moved through southeast Michigan. This storm produced a great deal of lightning and heavy rainfall throughout eastern Michigan. Most of the wind gusts with the strongest storms were in the 40 to 50 MPH range, however, a few isolated severe wind reports were received. An estimated 20,000 homes and businesses were left without power in the metro Detroit Area following the storms.
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 Detroit, MI wrote its last area forecast discussion before the first event at Jul 21, 10:45 AM EST, 1 hour 45 minutes earlier.
SOUTHEAST MICHIGAN AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1145 AM EDT SUN JUL 21 2002
SEVERE WEATHER THREAT AND THE HEAT WILL BE THE MAIN CONCERNS FOR
THIS AFTERNOON. THE STRONG SURFACE COLD FRONT EXTENDING FROM
NORTHERN LAKE MICHIGAN BACK INTO THE MID MISSISSIPPI VALLEY WILL
PUSH THROUGH SOUTHEAST MICHIGAN FROM 20Z TO 00Z...PER THE LATEST RUC
SOLUTION. VERY HIGH INSTABILITY AHEAD OF THIS FRONT IS ALREADY
ALLOWING THUNDERSTORMS TO DEVELOP IN FAR SOUTHERN LOWER MICHIGAN AND
NORTHERN INDIANA. UPPER LEVEL SUPPORT FOR THE THUNDERSTORMS WILL
COME FROM SOME LIFT AHEAD OF THE SHORT WAVE TROUGH OVER THE UPPER
MISSISSIPPI VALLEY AND DIVERGENCE ALOFT IN ENTRANCE REGION OF UPPER
JET OVER THE NORTHERN GREAT LAKES. MODIFIED 12Z KDTX SOUNDING FOR A
TEMP OF 94 AND DEWPOINT OF 75 GIVES A CAPE OF 5200 J/KG. MODEL
SOUNDING FOR THIS AFTERNOON ARE STILL SHOWING SOME DRYING IN THE MID
LEVELS. THIS DRIER MID LEVEL AIR WAS NOTED ACROSS ILLINOIS ON THE
12Z RAOBS. SO ALTHOUGH 0-6KM SHEAR PROFILES ARE NOT THAT
STRONG...NEGATIVE BUOYANCY POTENTIAL AND THE INSTABILITY SHOULD BE
ENOUGH TO ALLOW SOME STORMS TO PRODUCE DAMAGING WINDS. PRECIPITABLE
WATER VALUES NEAR 2 INCHES AND K INDICES IN THE UPPER 30S WILL ALSO
SPELL GOOD POTENTIAL FOR HEAVY RAINFALL WITH THE STORMS. TIMING THE
ONSET OF THE STORMS WILL BE DIFFICULT AS DIFFERENTIAL HEATING
BOUNDARIES AND THUNDERSTORM OUTFLOW WILL AID DEVELOPMENT WELL IN
ADVANCE OF THE SURFACE COLD FRONT.
A HEAT ADVISORY HAS ALSO BEEN ISSUED FOR THE SOUTHERN 2/3RDS OF THE
FORECAST AREA BASED ON CURRENT HEAT INDICES. SOME LOCATIONS MAY NOT
ATTAIN ADVISORY CRITERIA DUE TO ONGOING THUNDERSTORMS. WITH A GOOD
BIT OF CLEARING UPSTREAM THOUGH...THINK THAT THERE WILL BE SEVERAL
LOCATIONS THAT HAVE HEAT INDICES AROUND 105 DEGREES FOR MUCH OF THE
AFTERNOON.
.DTX...HEAT ADVISORY...THIS AFTERNOON...
MIZ060>063-068>070-075-076-082-083
CONSIDINEMIZ047>049-053>055-060>063-068>070-075-076-082-083-212100- HAZARDOUS WEATHER OUTLOOK FOR SOUTHEAST MICHIGAN NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI 1045 AM EDT SUN JUL 21 2002 ...HOT...HUMID WEATHER AND THUNDERSTORMS TODAY AND MONDAY... DISPATCHERS...PLEASE NOTIFY YOUR EMERGENCY MANAGERS IMMEDIATELY. HAZARDS... EXCESSIVE HEAT AND HUMIDITY WILL AFFECT ALL OF SOUTHEAST MICHIGAN TODAY...WITH TEMPERATURES INCHING ABOVE 90 AND HEAT INDICES APPROACHING 100. IN ADDITION...NUMEROUS THUNDERSTORMS ARE EXPECTED THROUGH EARLY TO MID AFTERNOON NORTH OF M59. THESE THUNDERSTORMS ARE EXPECTED TO PRODUCE WIND GUSTS TO 45 MPH AND PEA SIZE HAIL. NO SEVERE WEATHER IS EXPECTED AT THIS TIME. DISCUSSION... LOW PRESSURE NORTH OF LAKE SUPERIOR WILL CONTINUE TO TRACK EAST TODAY...AND SOUTHWEST WINDS AHEAD OF THIS SYSTEM WILL PUMP HOT AND HUMID AIR INTO SOUTHEAST MICHIGAN. HIGH TEMPERATURES WILL CLIMB ABOVE THE 90 DEGREE MARK THIS AFTERNOON WITH DEWPOINTS CLIMBING ABOVE THE 70 DEGREE MARK... ESPECIALLY IN AREAS SOUTH OF M59. THIS COMBINATION WILL RESULT IN HEAT INDEX VALUES REACHING AROUND THE 100 DEGREE RANGE. AS HEAT INDICES APPROACH OR EXCEED THE 100 MARK...IT IS BEST TO AVOID PROLONGED OUTSIDE ACTIVITIES TO PREVENT HEAT STRESS. IN ADDITION...THE INCREASE IN MOISTURE WILL LEAD TO AN UNSTABLE AIRMASS...WHICH WILL CONTRIBUTE TO NUMEROUS THUNDERSTORMS NORTH OF M59 THIS AFTERNOON AND THIS EVENING. VERY HEAVY RAINFALL...PEA SIZE HAIL AND WIND GUSTS UP TO 45 MPH WILL BE THE MAIN HAZARDS WITH THESE STORMS. THE STORMS WILL MOVE TO THE SOUTHEAST AT 25 MPH. SPOTTER ACTIVATION... SPOTTER ACTIVATION NOT ANTICIPATED AT THIS TIME... ALTHOUGH THUNDERSTORM DEVELOPMENT WILL BE MONITORED FOR INCREASES IN INTENSITY. OUTLOOK FOR MONDAY AND TUESDAY... A COLD FRONT WILL MOVE THROUGH SOUTHEAST MICHIGAN MONDAY AFTERNOON. MORNING SUNSHINE WILL ALLOW TEMPERATURES TO RISE WELL INTO THE 90S. HEAT INDICES ARE EXPECTED TO REACH INTO THE 105 TO 110 DEGREE RANGE FOR AREAS ALONG AND SOUTH OF INTERSTATE 69. IN ADDITION...SEVERE THUNDERSTORMS WILL BE POSSIBLE WITH THE PASSAGE OF THE COLD FRONT MONDAY AFTERNOON AND EVENING. NO HAZARDOUS WEATHER IS EXPECTED ON TUESDAY AS CONDITIONS WILL BE DRY AND COOLER. STAY TUNED TO NOAA WEATHER RADIO... OR LOCAL MEDIA OUTLETS... FOR THE LATEST FORECAST INFORMATION FROM THE NATIONAL WEATHER SERVICE. YOU CAN ALSO OBTAIN THE LATEST FORECAST ON THE NATIONAL WEATHER SERVICE WEB SITE. HTTP://WWW.CRH.NOAA.GOV/DTX/ (ALL LOWER CASE) SF/RBP
The Detroit radar (KDTX), 37 km away, was scanning. The volume nearest the first event began at 17:30 UTC.
2 thunderstorm wind. Local standard time, as filed.
Spotters reported that several large tree branches were blown down in thunderstorm winds.
A newspaper reported that a large tree blew over in thunderstorm winds and fell onto a man, trapping him in his back yard.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Michigan in 2002Every state in 2002This day in weather historyWarnings in Michigan, July 2002
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: 5303711, 5303710.