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Corey M. Mead and Jeremy S. Grams (May 11, 2011). "May 11, 2011 1300 UTC Day 1 Convective Outlook". Storm Prediction Center. National Oceanic and Atmospheric Administration. Retrieved May 17, 2011.
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Unattributed (May 13, 2011). "Tornadoes cause damage in western South Dakota May 9". National Weather Service Office in Rapid City, South Dakota. National Oceanic and Atmospheric Administration. Retrieved May 17, 2011.