Ingredients are coming together across parts of the Midwest and Ohio Valley for a dangerous outbreak of severe weather with widespread wind damage similar to that of a derecho. Meteorologists are concerned that an initial tornado threat Wednesday afternoon and evening could evolve into a complex of storms with widespread wind damage occurring.

Some of the cities and towns most at risk for severe weather into Wednesday night include Chicago, Ill.; Columbus, Ohio; Fort Wayne, Ind.; Aurora, Ill.; Dayton, Ohio and Louisville, Ky., to name a few.

Strictly speaking, a derecho is a widespread, long-lived wind storm that is associated with a band of rapidly moving showers or thunderstorms. These showers and thunderstorms produce wind damage over a large swath of land.

While wind gusts form derechos can sometimes reach speeds over 80 or even 100 mph, the vast majority of observed wind reports are usually between 60 and 70 mph.


Additionally, these kinds of wind speeds can cause minor damage to structures, including roofs on houses, and they can easily blow around any unsecured objects left outside.

Even if a derecho does not evolve Wednesday night, powerful thunderstorms will still be quite numerous across much of Illinois, Indiana and Ohio.

What Is a Derecho?
The June 2012 Derecho Event
Severe Weather Center

Thunderstorms will begin along a corridor from east-central Iowa through northern Illinois Wednesday afternoon into Wednesday evening. The thunderstorms that develop initially in this location will have the ability to take on some rotation, and a few tornadoes are possible, especially in and around Davenport, Iowa, Rockford, Ill.; Sterling Ill.; Ottawa, Ill. and Chicago.

The thunderstorms will then begin to congeal into a bowing, or backward 'C' shaped line as they reach northern Indiana and southwestern Michigan. How much of a bowing shape the thunderstorms can take on will play a role in determining how much wind the storms can produce, and ultimately, whether or not a "derecho" fully evolves.

The worst of the storms will likely be in the afternoon and evening across western Iowa into northern Illinois and Indiana. In places such as Ohio, the most dangerous storms may hold out until the evening hours or even after dark. Still, there could still be a stray thunderstorm around even before the main line arrives.


Once thunderstorms develop, they will strengthen quickly, and dangerous conditions could follow soon after.

One added concern across the region will be very heavy, potentially flooding rain. This storm system will have the ability to produce a large area of 2-3 inches from Chicago into Detroit, Cleveland and Pittsburgh. Rain of this magnitude, on top of already saturated soil, will cause flash flooding and the possibility of renewed flooding or larger waterways.

