SIOUX CITY, Iowa/Chicago, Illinois (KCAU/WGN) – WGN out of Chicago, Illinois, has a weather blog where viewers send in weather-related questions for Chief Meteorologist Tom Skilling to answer.
John Posulka, a viewer from Wolverine, Michigan reached out to Tom Skilling to ask him about the atmospheric conditions needed to produce a derecho.
Tom Skilling responded to Posulka’s question.
A derecho develops from an organized cluster of thunderstorms that evolves into a bow echo.
Thunderstorm development requires warmth, moisture, instability and lift and bow echoes can form when the winds aloft are strong with little change of direction with height.
As rain-cooled thunderstorm downdrafts strike the surface, they spread out in the direction of the storm movement forming a gust front, generating wind gusts in excess of 60 mph and sometimes in excess of 100 mph.
The storm complex must travel at least 250 miles to be called a derecho and the length of the line can range from about 50 to several hundred miles.
While most derecho damage is from straight-line winds, small tornadoes are often embedded in the storms.