August 22, 2007: Straight-line wind in Dodge and Waukesha Counties

During the afternoon and evening hours of August 22nd, the second round of storms for the calendar day moved east across south-central and southeast Wisconsin. The clusters or short lines of storms moved east at a speed of about 30 knots (35 mph), and generated damaging downburst straight-line winds that toppled trees and power-lines, and heavy rains that triggered flash flooding. Synoptically, a stationary front stretched from northern Iowa to Wisconsin/Illinois border. Warm, moist, unstable air flowed north over the front in association with an upper-level short-wave trough, resulting in thunderstorm generation. Hourly rainfall rates peaked around 2 inches.||By the end of August, 2007, many locations in south-central and southeast Wisconsin would establish new August rainfall records, and all-time/any month rainfall records. Many locations measured 10 to over 20 inches for the month of August, 2007, or about 200% to over 400% of normal. Normal August precipitation in southern Wisconsin is about 4 to 4.25 inches. Unofficially, about 25 inches fell at a location 2W of Barneveld, Iowa County. Specific August, 2007, monthly totals are listed in the various flash flood events of August 18-19th and August 22nd.