Tornado simulation. Ming Xue of the University of Oklahoma used the Pittsburgh Supercomputing Center's (PSC) terascale computer system to run one of the largest tornado simulations ever created. Together with PSC's Greg Foss, who used Xue's numeric simulations to create a 3-D visualization, Xue successfully simulated a 1977 supercell thunderstorm and the high-intensity tornado that it spawned. The results captured the tornado's vortex structure with wind speeds of 260 miles per hour, classified as an F5 on the Fujita tornado intensity scale.

Xue is a team member with the $40 million NSF ERC for Collaborative Adaptive Sensing of the Atmosphere (CASA). A complete summary of the simulation project is available at casa.umass.edu/docs/Retwistered_twister.pdf. The research was supported by NSF grants ATM 01-29892 and EEC 03-13747. (Date of Image: May 2004).

Credit: Numerical simulation performed by Dr. Ming Xue, Center for Analysis and Prediction of Storms and School of Meteorology, University of Oklahoma; 3-D visualization created by Greg Foss, Pittsburg Supercomputing Center, with assistance from Ming Xu.

Damage from the Moore Tornado that struck Moore, Okla., on May 20, 2013. Twenty-four people were killed and thousands of structures were destroyed--many were completely flattened.

The May 18-21, 2013, tornado outbreak was significant, affecting parts of the Midwestern United States and lower Great Plains. This event occurred just days after a deadly outbreak struck Texas and surrounding Southern states on May 15. On May 16, a slow moving trough (an elongated region of relatively low atmospheric pressure) crossed the Rocky Mountains and traversed the western Great Plains. Initially, activity was limited to scattered severe storms; however, by May 18, the threat for organized severe thunderstorms and tornadoes greatly increased. A few tornadoes touched down that day in Kansas and Nebraska, including an EF4 near Rozel, Kan.

Maintaining its slow eastward movement, the system produced another round of severe weather nearby. Activity significantly increased on May 19, with tornadoes confirmed in Oklahoma, Kansas, Iowa, Missouri and Illinois. In Oklahoma, two strong tornadoes (one was rated EF4) caused significant damage in rural areas of the eastern Oklahoma City metropolitan area; two people lost their lives in Shawnee. However, the most dramatic events occurred the next day with the devastating Moore Tornado.

Credit: This image was taken by Roger M. Wakimoto while performing tornado research for the University of Colorado, Boulder. Wakimoto is the assistant director for the National Science Foundation's (NSF) Directorate for Geosciences.