After a tornado leveled Moore, Okla., last year, firefighter Shonn Neidel (left) developed an app that helps first responders locate storm shelters under the wreckage.
Courtesy of Shonn Neidel
A severe thunderstorm wall cloud is seen over the area of Canton, Miss., on Tuesday. At least 35 people in six states have been killed by tornadoes unleashed by a ferocious storm system this week.
Travel trailers and motor homes were piled on top of each other at Mayflower RV in Mayflower, Ark., on Sunday after tornadoes carved through the central and southern U.S.
This ominous-looking wall of clouds formed near Purcell, Okla., on Thursday. There were more tornadoes in Oklahoma and Arkansas as severe weather continued to pummel those states.