Storm Record · Dane, Walworth, Waukesha Counties
August 9, 2009: Straight-line wind in Dane, Walworth and Waukesha Counties
What the National Weather Service recorded
Three rounds of thunderstorms produced wind damage and flash flooding during the afternoon, evening, and overnight hours of August 9th. The thunderstorms developed as a cold front trailing from low pressure over northeast Wisconsin moved into a hot, humid and unstable air mass in place over southern Wisconsin. Temperatures warmed to 85 and 90 degrees, with dew-points in the 70s. Strong unidirectional vertical wind shear produced bowing line segments that caused damaging wind gusts. The thunderstorms produced heavy rainfall as precipitable water values reached 1.8 to 2 inches. All together, in just southeast Wisconsin, at least 28,000 customers lost electrical power. It was reported that 140 power-lines came down due to tree debris, and at least a dozen or two utility poles snapped.
Source: NOAA Storm Events Database · episode 33333
Every report, in the Weather Service's words
Where It Hit
| Location | County | Hazard | Size | Report |
|---|---|---|---|---|
| Lake Geneva | Walworth | Wind | 75 mph wind | Numerous public reports were made of trees blown down and power lines down in the city of Lake Geneva. |
| Daleyville (3 S) | Dane | Wind | 75 mph wind | Emergency Management reported large trees and power lines down in extreme southwestern Dane County, south of Daleyville, along Drammen Valey Rd. This damage was an extension of a damage swath that extended west into Iowa County and south-southwest into northwestern Green County and northeastern Lafayette County. |
| Delavan (2 SE) | Walworth | Wind | 74 mph wind | Numerous trees and power lines were blown down by thunderstorm wind gusts. The gusts were measured to 74 mph, with sustained winds of 59 mph, on weather equipment owned by a ham radio operator near Delavan. A television meteorologist estimated wind gusts in Lake Geneva of 52 knots. |
| Muskego (2 SE) | Waukesha | Wind | 70 mph wind | Powerful thunderstorm wind gusts toppled large trees and generated tree debris that brought down some power lines. |
| East Troy (2 E) | Walworth | Wind | 66 mph wind | Tree damage from near Beulah Station (east of city of East Troy) to Honey Creek was noted by a trained spotter. Based on the size of the limbs and trees blown down they estimated winds in excess of 52 knots (60 mph). |
| Eagle | Waukesha | Wind | 64 mph wind | Police reported trees down in the village of Eagle with estimated wind gusts of 56 knots (65 mph). |
| Dane | Dane | Wind | 64 mph wind | Large trees uprooted and large limbs were knocked out of trees by powerful gusts with heavy rains. |
| Downtown Waukesha (2 SE) | Waukesha | Wind | 60 mph wind | Trees were reported to be blown down by thunderstorm wind gusts on the southeast side of the city of Waukesha by a trained spotter. |