Tornadoes devastated the southern United States during the spring of 2011. Six EF-5 tornadoes touched down to set records in death and destruction. Tuscaloosa, Alabama and Joplin, Missouri were the most notable. These weather events did not occur without contributing conditions. Unusually warm humid conditions in the lower atmosphere and cooler conditions in the upper atmosphere combined with wind direction changes and increased wind speed to bring the intense, counter-cl