July 11, 2011 Derecho

Widespread Damaging Winds Across Portions of the Region

A complex of severe thunderstorms raced across the region on July 11, producing widespread wind damage in portions of northern Indiana, southern Michigan, and northwest Ohio. The thunderstorm complex developed on the northern periphery of a staunch upper level ridge in place across the southern US. A middle atmospheric disturbance ejected out of the western US and supported the development of thunderstorms across eastern Colorado, northwest Kansas, and southwest Nebraska. The thunderstorm’s outflow congealed and a Mesoscale Convective System developed. The thunderstorm complex remained on an eastward trajectory, following the gradient of instability and the mid-level atmospheric flow, failing to build south into the most unstable air due to intense low level capping in place. Hence, this type of system is commonly referred to as a “ridge rider” as the system remains on the edge of the upper level ridge as they propagate. This complex of severe thunderstorms produced wind damage from southwest Nebraska to Maryland, approximately 1,400 miles with the strongest winds from central Iowa and east. A convective system that produces widespread wind damage for several miles is known as a derecho. (Click here to learn more about derechos.) Winds gusted as high as 85 mph, with damage to structures and trees. The hardest hit part of the local area was along the Indiana and Michigan state line. A radar overview and map of storm reports is included below.

Loop of radar with storm reports from July 11.

JC