National Oceanic and Atmospheric Administration - National Severe Storms Laboratory. "Tornadoes: Nature's Most Violent Storms" [Online]. 18-March-2004. http://www.nssl.noaa.gov/NWSTornado/
National Weather Service - Storm Prediction Center. "The Tornado FAQ: Frequently Asked Questions about Tornadoes" [Online]. 18-March-2004. http://www.spc.noaa.gov/faq/tornado/