Flash Flood and Hail in Wisconsin, August 11, 2002

Name: Flash Flood and Hail in Wisconsin, August 11, 2002
Start: 2002-08-11T15:15
End: 2002-08-11T19:00
Location: Wisconsin

August 11, 2002 · NWS MKX · 7 events in 2 counties and zones

Where it happened

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.

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: $400,000
Crop damage: $200,000
Events: 7

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 MKX wrote it up.

A cluster of severe thunderstorms dumped large hail in parts of southern Sauk County, and then dissipated. Another cluster of severe thunderstorms blossomed over western Dane County, resulting in wind, hail, and flash flood damage in the Pine Bluff area, west of the Madison metro-area. In the Pine Bluff area, hurricane-force downburst winds reached estimated speeds of 70 kts (80 mph), resulting in toppled trees and power lines. The fringe effects of this powerful macro-burst resulted in some tree damage north to the Cross Plains to Middleton area. The thunderstorm cluster also produced hail up to 2 inches in diameter in the Pine Bluff area, resulting in major damage to at least 100 vehicles, and to roofs and siding of homes. A one-mile swath of corn was leveled on the north side of Pine Bluff. Up to 4.50 inches of rain fell in the Pine Bluff area in a short period of time, resulting in flash flooding that washed out gravel shoulders of several roads in the Pine Bluff to Middleton area. At least a dozen homes sustained water damage to basement contents due to accumulating water up to 5 feet in depth. Powerful thunderstorm winds also damaged trees and power lines in the Waunakee area north of Madison. The concentration of damage in the Pine Bluff was the result of a series of thunderstorm cells developing in a stationary initiation location in western Dane County. As each cell developed and moved east-northeast, a new cell would would replace it on the backside, aprocess referred to as "back-building." Thunderstorm development was focused by strong warm-air advection between the surface and 10,000 feet above ground coupled with strong surface moisture convergence from eastern Iowa into south-central Wisconsin. Surface dewpoints were in the 60s.

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 Milwaukee, WI wrote its last area forecast discussion before the first event at Aug 11, 1:15 PM CST, 2 hours earlier.

Area forecast discussion, Aug 11, 1:15 PM CST, 2 hours before

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI
215 PM CDT SUN AUG 11 2002

FCST FOCUS ON TIMING...COVERAGE OF PCPN WITH APPROACHING FRONT.

SOME WEAK BNDRY LAYER MOISTURE CONVERGENCE GENERATING SUSPICIOUS
CLOUDS OVR PORTIONS OF CENTRAL WI EXTENDING INTO OUR NRN CWA. NOT
ENOUGH TO SHOW UP ON RADAR YET. AM A BIT CONCERNED WE COULD SE A
ROGUE SHOWER OR STORM BEFORE COOLING SETS IN THIS EVENING.  AIR BELOW
ABOUT 6KFT IS VERY DRY ACROSS MUCH OF THE CWA AND THIS HAS MIXED TO
THE SURFACE WITH SFC DWPNTS IN THE MID 50S TO LOWER 60S...VERSUS THE
UPR 60S TO LOWER 70S WE HAD THIS MORNING.  IT WILL BE HARD FOR ANY
PCPN TO DEVELOP/PERSIST EARLY THIS EVENING.  PLAN TO KEEP IT DRY
UNTIL MONDAY AFTNOON...WILL HAVE TO MAKE A LAST MINUTE CALL.

WELL DEFINED FRONT AT 12Z MON SHOULD STRETCH FROM NCNTL MN VCNTY TO
SCNTRL NEB.  AS THE DAY PROGRESSES...THE PARENT LOW OVR LK
WINNEPEG VCNTY BEGINS TO WEAKEN AND LIFTS SLOWLY NE.  SIMILAR ACTION
OCCURES AT H5.  AS A RESULT THE FRONT GRADUALLY LOOSES ITS
DEFINITION AND BECOMES PINCHED BY A RIDGE OVER THE OHIO VALLEY AND
NRN HIGH PLAINS.  ALL SHOULD NOT BE LOST HOWEVER. THE AIR AHEAD OF
THE BNDRY WILL BE VERY WARM AND MODERATELY MOIST.  SFC BASED CAPES
REACH ABOUT 2000J/KG.  EXPECT FRONT TO LIGHT UP WEST OF CWA IN THE
AFTERNOON...THEN TRACK ON IN DURING THE EVENING. THE FRONT LACKS A
STRONG PUSH WITH THE UPR FLOW MORE OR LESS PARALLEL WITH THE BNDRY.
RESULTANT WEAKENING LLV FORCING SHOULD CAUSE THE CONVECTION TO
DIMINISH AS COOLING SETS IN DURING THE EVENING. ETA DEPICTS THIS.
HOPEFULLY...WE CAN SEE THIS PCPN TRACK ACROSS THE ENTIRE CWA BEFORE
DIMINISHING.

UPR TROF SLOWS OVR THE REGION MON NGT-TUE IN RESPONSE TO ANOTHER
PIECE OF ENERGY COMING OUT OF THE PACIFIC NORTHWEST.  THIS CAUSES THE
FRONT TO SLOW DOWN.  MODELS HAVE THE FRONT JUST EAST OF THE AREA WHEN
THIS HAPPENS.  A WEAK LOW IS FORECAST TO MOVE UP THE FRONT AND
MAINLY AFFECT AREAS JUST TO OUR EAST TUE INTO WED.  IF THIS FRONT
SLOWS DOWN BEFORE MOVING EAST OF US...WE MAY BENEFIT FROM THIS
SECOND WAVE.  PROGRESSIVE PATTERN AND COMPLEXITIES WITH EXPECTED
CONVECTION MAKE THIS TIMING/PLACEMENT DIFFICULT.

ETA TEMPS HAVE BEEN A NOTCH TOO HIGH LATELY...BUT MUCH BETTER THAN
THE OTHERS...WILL STICK WITH ETA 2M TEMPS ADJUSTED FOR LATEST BIAS.

.MKX...NONE.

DAVIS

REM

The radar

The La Crosse radar (KARX), 104 km away, was scanning. The volume nearest the first event began at 21:16 UTC.

Open the radar archive at this moment

Event by event

4 hail, 2 thunderstorm wind, 1 flash flood. Local standard time, as filed.

Hail, Sauk

When: August 11, 3:15 PM CST
Where: Sauk County, 4 mi WNW of Plain
Measured: 1.5 in hail
Reported by: GENERAL PUBLIC
Coordinates: 43.300, -90.117

Hail, Sauk

When: August 11, 3:40 PM CST
Where: Sauk County, 5 mi SE of Black Hawk
Measured: 0.75 in hail
Reported by: POST OFFICE
Coordinates: 43.217, -89.867

Hail, Dane

When: August 11, 4:05 PM CST
Where: Dane County, 1 mi S of Mazomanie
Measured: 0.75 in hail
Reported by: TRAINED SPOTTER
Coordinates: 43.150, -89.783

Thunderstorm Wind, Dane

When: August 11, 5:05 PM CST
Where: Dane County, Waunakee
Measured: 56 kt (64 mph)
Reported by: LAW ENFORCEMENT
Coordinates: 43.183, -89.450

Hail, Dane

When: August 11, 5:05 PM CST to 5:20 PM CST
Where: Dane County, Pine Bluff
Measured: 2 in hail
Property damage: $200,000
Crop damage: $100,000
Reported by: LAW ENFORCEMENT
Coordinates: 43.067, -89.650

Thunderstorm Wind, Dane

When: August 11, 5:05 PM CST to 5:20 PM CST
Where: Dane County, Pine Bluff
Measured: 70 kt (81 mph)
Property damage: $100,000
Reported by: LAW ENFORCEMENT
Coordinates: 43.067, -89.650

Flash Flood, Dane

When: August 11, 5:15 PM CST to 7:00 PM CST
Where: Dane County, Pine Bluff
Property damage: $100,000
Crop damage: $100,000
Reported by: LAW ENFORCEMENT
Coordinates: 43.067, -89.418 (the zone’s center; the record gives no point)

What these are

Hail: Hail three-quarters of an inch or larger, or smaller hail that caused damage, filed with the largest stone measured.
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.
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.

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

The same day elsewhere

Every storm in Wisconsin in 2002 Every state in 2002 This day in weather history Warnings in Wisconsin, August 2002

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: 5314809, 5314808, 5314810, 5314811, 5314812, 5314813, 5314814.