"Storm Reports for May 21, 2011". Storm Prediction Center. National Oceanic and Atmospheric Administration. May 21, 2011. Archived from the original on May 25, 2011. Retrieved May 22, 2011.
"Storm Reports for May 22, 2011". Storm Prediction Center. National Oceanic and Atmospheric Administration. May 22, 2011. Archived from the original on May 25, 2011. Retrieved May 22, 2011.
Mead, Corey M. (May 24, 2011). Particularly Dangerous Situation (PDS) Tornado Watch 356. Storm Prediction Center (Report). Norman, Oklahoma: National Oceanic and Atmospheric Administration. Archived from the original on September 3, 2014. Retrieved May 24, 2011.
"Storm Reports for May 21, 2011". Storm Prediction Center. National Oceanic and Atmospheric Administration. May 21, 2011. Archived from the original on May 25, 2011. Retrieved May 22, 2011.
"Storm Reports for May 22, 2011". Storm Prediction Center. National Oceanic and Atmospheric Administration. May 22, 2011. Archived from the original on May 25, 2011. Retrieved May 22, 2011.
Mead, Corey M. (May 24, 2011). Particularly Dangerous Situation (PDS) Tornado Watch 356. Storm Prediction Center (Report). Norman, Oklahoma: National Oceanic and Atmospheric Administration. Archived from the original on September 3, 2014. Retrieved May 24, 2011.
Jim LaDue; Tim Marshall & Kevin Scharfenberg (2012). "Discriminating EF4 and EF5 Tornado Damage"(PDF). National Weather Service Office in Norman, Oklahoma. National Oceanic and Atmospheric Administration. Archived from the original on January 9, 2016. Retrieved June 26, 2013.
Jim LaDue; Tim Marshall & Kevin Scharfenberg (2012). "Discriminating EF4 and EF5 Tornado Damage"(PDF). National Weather Service Office in Norman, Oklahoma. National Oceanic and Atmospheric Administration. Archived from the original on January 9, 2016. Retrieved June 26, 2013.