"Severe Weather 101: Tornado FAQ". National Severe Storms Laboratory. NOAA. January 29, 2007. Archived from the original on October 30, 2013. Retrieved September 29, 2013.
"Severe Weather 101: Tornado FAQ". National Severe Storms Laboratory. NOAA. January 29, 2007. Archived from the original on October 30, 2013. Retrieved September 29, 2013.
"Tornado FAQ". Storm Prediction Center. NOAA. January 29, 2007. Archived from the original on March 2, 2012. Retrieved September 29, 2013.