Tornadoes and storms that hit US were a derecho, says National Weather Service

The storm system hit the north-central US on 15 December, separately from the record, killer tornadoes that devastated a swath of states but caused most damage in Kentucky on the night of 10 December.

Derechos are relatively rare events, and in the US are more likely to occur in the area dubbed the Corn belt that ranges from Minnesota and Iowa south and eastward toward the Ohio Valley, according to the National Weather Service.

The December derecho is the first on record, as they are more likely to occur from May through August, and particularly during periods of high heat.

Ryan Maue, an Atlanta-based private meteorologist and former chief scientist for the National Oceanic and Atmospheric Administration, told the Associated Press that a derecho can develop from a series of separate storms, usually carrying hail and strong winds, that combine and build into a larger complex.

A 2009 storm dubbed a super derecho by the NWS traveled from western Kansas to eastern Kentucky, causing several deaths and injuries, along with over $500 million in damages by the time it had traveled over 1,000 miles.

High wind warnings were issued for a large area from New Mexico to upper Michigan. According to poweroutage.us, which tracks utility reports, more than 400,000 homes and businesses were without electricity in Michigan, Wisconsin, Iowa and Kansas.

At least five people died as a result of the storms.