Flash Flood and Flood in Illinois, July 21, 2001

Name: Flash Flood and Flood in Illinois, July 21, 2001
Start: 2001-07-21T17:10
End: 2001-07-21T20:35
Location: Illinois

July 21, 2001 · NWS LOT · 6 events in 4 counties and zones

Thunderstorms formed along a lake breeze in northeast Illinois during the late afternoon and evening of Saturday, July 21st. Trees were blown down in Monee in Will county at 1710 CST.

Where it happened

Every event with a place to put it; 3 filed by county or forecast zone are drawn at its center, in a lighter ring. 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: $520,000
Crop damage: None recorded
Events: 6

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.

Thunderstorms formed along a lake breeze in northeast Illinois during the late afternoon and evening of Saturday, July 21st. Trees were blown down in Monee in Will county at 1710 CST. One 12 inch diameter tree was blown down in Orland Park in Cook county at 1740 CST and numerous trees were blown down in Tinley Park at 1745 CST. Trees were also blown down east of Beaverville and east of Askkum in Iroquois county. Approximately 30,000 customers lost power from the storms. Lightning struck a house in Tinley Park and ignited the roof on fire, causing significant damage to the roof.But the main damage from these thunderstorms was torrential rainfall. The heaviest rain fell across southwest Cook county, extreme northeast Will county and central Dupage county. Water burst through a basement foundation in Tinley Park in Cook county. Water filled the basement and topped out at 6 feet, 11 inches deep. Several homes in Orland Park and Tinley Park had 2 to 4 feet of water in basements. Streets were also flooded in these areas. In Dupage county, one foot of water was reported across Main Street in Wheaton and the road was closed. Other roads had standing water. Some rainfall totals from this event include 3.08 inches in Olympia Fields, 2.79 inches in Park Forest, 2.30 inches in Winfield, and 2.03 inches in Glenwood. There were no reports of injuries.

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, 1:45 PM CST, 3 hours 25 minutes earlier.

Area forecast discussion, Jul 21, 1:45 PM CST, 3 hours 25 minutes before

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO IL
245 PM CDT SAT JUL 21 2001

THE NUMBERS ARE IN FOR TOMORROW AND MAY BE A BIT OVERDONE
CONSIDERING RH AND RANDOM CLOUD COVER. MCS DEVELPMENT IN SRN MN AND
IA NOT PICKED UP ON MODELS. CORFIDI VECTORS WOULD SUGGEST STUFF IN
SRN MN EARMARKED FOR NRN IL THIS EVENING AND ERLY TONIGHT. IF LITTLE
PCPN BY THE TIME IT ARRIVES...WILL BE MORE CLOUD COVER TO KEEP TEMPS
UP TONIGHT AND DEPARTING BY MRNG TO ALLOW GOOD AMOUNT OF SUNSHINE.
WITH THAT IN MIND...TEMPS SHOULD HAVE LITTLE PROBLEM REACHING 90+
AGAIN ON SUNDAY. THUS WILL UPGRADE EXCESSIVE HEAT WATCH TO WARNING
TO BE IN EFFECT SUNDAY.

850 THERMAL RIDGE EDGING EAST OVER NWRN IL TMRW AND JUSTIFYING
WARMER TEMPS FOR THE AREA WEST OF CHI. RFD ALREADY REACHED 92 WITH
GOOD PROSPECT OF 95 TMRW. THIS CUD MEAN HI VALUES AROUND 105.
COORDINATION WITH SURROUNDING WFO'S SUGGEST ADVISORY FOR ALL CWA
WITH WARNING CRITERIA FOR THE 8 COUNTY CHICAGO AREA.

THIS RIDGE EDGES FURTHER EAST MONDAY WITH ENHANCED 850 JET. IF NO
PCPN OR THICK CLOUD COVER...CUD CONTINUE HEAT WRNG/ADV INTO MONDAY.

NOW FOR PCPN. STILL SOME SPORADIC SHOWERS DEVELOPING IN AREA...BUT
LARGER CONCERN IS AREA IN MN AND IA...WHICH APPEARS TO BE DYING. WLL
PUT IN CHC TNGT FOR SHWERS 30%...BUT LEAVE OUT TOMORROW. BETTER
DYNAMICS APPEARING SUNDAY NIGHT WITH NEARLY ADIABATIC LAPSE BELOW
800 MB...SHEARED WIND PROFILE...AND CAPES AROUND 4K. QUESTION IS
WILL IT CONT (CLDS AND/OR PCPN) INTO MONDAY. MODELS SAY THERE IS A
CHC ON MONDAY WITH TROF MOVING THRU MONDAY EVENING. THERMAL RIDGE
NOT MOVING SOUTH OF AREA UNTIL TUESDAY NIGHT WITH ACTUAL PASSAGE OF
COLD FRONT. THUS TUESDAY COULD BE ANOTHER EXTENSION OF HOT WEATHER.

AVN BRING FNT THRU DRY ON TUESDAY WHICH SEEMS ODD AND WILL KEEP CHC
GOING. NE WINDS OVER AREA THRU FRIDAY SHUD KEEP RETURN MOISTURE
SOUTH OF AREA...PSBLY RAINING ACRS NWRN AND CNTL IL. MAY RETURN CHC
RAIN TO AREA FRIDAY NIGHT AND SATURDAY.

.CHI...EXCESSIVE HEAT WARNING FOR SUNDAY CHICAGO AREA/EXCESSIVE HEAT
ADV FOR SUNDAY REST OF CWA.

BRUMER

The radar

The Chicago radar (KLOT), 36 km away, was scanning. The volume nearest the first event began at 23:08 UTC.

Open the radar archive at this moment

Event by event

3 thunderstorm wind, 1 lightning, 1 flash flood, 1 flood. Local standard time, as filed.

Thunderstorm Wind, Will

When: July 21, 5:10 PM CST
Where: Will County, Monee
Measured: 50 kt (58 mph)
Reported by: LAW ENFORCEMENT
Coordinates: 41.417, -87.733

Lightning, Cook

When: July 21, 5:15 PM CST
Where: Cook County, Tinley Park
Property damage: $20,000
Reported by: NEWSPAPER
Coordinates: 41.895, -87.646 (the zone’s center; the record gives no point)

Flash Flood, Cook

When: July 21, 5:30 PM CST to 7:15 PM CST
Where: Cook County, Southwest Portion
Property damage: $500,000
Reported by: LAW ENFORCEMENT
Coordinates: 41.895, -87.646 (the zone’s center; the record gives no point)

Thunderstorm Wind, Cook

When: July 21, 5:40 PM CST to 5:45 PM CST
Where: Cook County, Orland Park
Measured: 52 kt (60 mph)
Reported by: TRAINED SPOTTER
Coordinates: 41.633, -87.867

Thunderstorm Wind, Iroquois

When: July 21, 7:00 PM CST to 7:17 PM CST
Where: Iroquois County, 3 mi E of Beaverville
Measured: 50 kt (58 mph)
Reported by: LAW ENFORCEMENT
Coordinates: 40.950, -87.600

Flood, Du Page

When: July 21, 7:35 PM CST to 8:35 PM CST
Where: Du Page County, Wheaton
Reported by: EMERGENCY MANAGER
Coordinates: 41.852, -88.086 (the zone’s center; the record gives no point)

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.
Lightning: A lightning strike that killed, injured or caused damage.
Flash Flood: Flooding that begins within six hours of the rain that causes it, or of a dam or levee failure or ice jam release, often with deadly speed.
Flood: Flooding that develops more slowly than a flash flood: rivers leaving their banks, or water standing over land for an extended time.

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

The same day elsewhere

Every storm in Illinois in 2001 Every state in 2001 This day in weather history Warnings in Illinois, July 2001

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: 5258119, 5258124, 5258121, 5258120, 5258122, 5258123.