Severe weather resulting in Tornadoes swept the Southern U.S killing more than 40 people over the past three days.

The worst affected region is North Carolina, which gets about 19 tornadoes a year, according to a data from the National Climatic Data Center. Other affected regions include Oklahoma, Alabama, Mississippi and Arkansas.

A tornado is a violent, dangerous, rotating column of air that is in contact with both the surface of the earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud.

More than 240 tornado reports came since Thursday-including several indicating EF-3 damage-according to National Weather Service.

Enhanced Fujita Scale (EF Scale) rates the strength of tornadoes in the United States based on the damage they cause. EF3 denotes Severe damage including destruction of entire stories of well-constructed houses, severe damage to large buildings such as shopping malls, trains overturned, trees debarked, heavy cars lifted off the ground and thrown and structures with weak foundations are badly damaged.

An average of 70 people are being killed by tornadoes in the U.S., according to Reuters. The tornado season runs from March to early July in the U.S.