Observations from the 23 August 2007 Chicago Derecho

During the afternoon and early evening of 23 August 2008, a progressive derecho affected the lower Great Lakes leaving a swath of widespread and locally significant (EF-1) straight-line wind damage. The derecho tracked across the heart of the Chicago metropolitan area during the mid-afternoon hours, leaving some of the most intense widespread wind damage that the Chicago area has seen from a convective event in decades.

Examination of radar reflectivity and velocity imagery from the WSR-88D, as well as the FAA's terminal Doppler radars from O'Hare and Midway Airports, revealed that two mesovortices formed along the leading edge of the derecho producing quasi-linear convective system as it moved through the Chicago Metropolitan area. Subsequent damage reports and ground surveys revealed that the most concentrated and significant wind damage was directly associated with the two mesovortices.

This study will look at various aspects of the pre-storm mesoscale environment which led to the development of this derecho and its associated mesovortices. Each mesovortex will be investigated to determine its overall characteristics and relationship to the degree of damage along each mesovortex path. In addition, radar imagery, including the higher resolution radar data from the terminal Doppler radars, will be examined and correlated to the resultant damage reports and tracks.