In the United States, tornadoes develop most often in the spring when warm moist unstable air accompanies strong fronts and fluctuating upper-air systems. There is a also a slight increase in tornado activity in late October and November. Tornadoes form least often in December and January so the tornadoes that occurred yesterday, Dec. 10, over the southeastern United States were unusual.
The Tropical Rainfall Measuring Mission (TRMM) satellite, managed by both NASA and the Japanese Space Agency was flying over the southeastern U.S. on December 10, 2012 at 1743 UTC (12:43 PM EST). As TRMM flew overhead its instruments captured data showing tornado spawning thunderstorms within a frontal system moving through Louisiana, Alabama, Mississippi and northern Florida. The image and animation created at NASA's Goddard Space Flight Center in Greenbelt, Md. shows a rainfall analysis from data captured with TRMM's Microwave Imager (TMI) and Precipitation Radar (PR) instruments. TRMM's Precipitation Radar (PR) found rain falling at a rate of over 77 mm/hr (~3 inches) in a few of these powerful storms. The locations of some of the tornado reported are shown overlaid in red.
Harold F. Pierce
SSAI/NASA Goddard Space Flight Center