Fewer Southeastern Tornadoes Occur Following Dry Falls and Winters

Rainfall irregularities as observed by NASA’s Tropical Rainfall
Measurement Mission  satellite. Credit: NASA

Perhaps Dorothy, from the famed film Wizard of Oz, should have hoped for a fall or wintertime drought. According to findings from a NASA-funded study published last June in Environmental Research Letters , dry fall and winter seasons in the southeastern United States mean it is less likely that Southern twisters will develop in springtime to sweep anyone off their feet.

Using rainfall data from NASA satellites, rain gauge information, and NOAA’s Storm Prediction Center tornado record dating back to 1952, University of Georgia meteorologists Marshall Shepherd and Tom Mote and Purdue University climatologist Dev Niyogi discovered a statistical tendency for drought-ravaged fall and winter seasons to pave the way for “below normal tornado days” in spring seasons that follow.


“This is conceptually similar to what Bill Gray’s been doing for more than 25 years when he predicts how active the hurricane season will be based on African rain,” said Shepherd, the study’s lead author, of the Colorado State University’s pioneer hurricane season forecaster.

They culled data from Northern Georgia and other parts of the southeast, but Shepherd and his colleagues believe their findings may have relevance for other regions. The new study also adds to the body of related work Shepherd and Niyogi are ushering, including their study earlier this year in the aftermath of Atlanta’s spring 2008 twister that linked urbanization and drought to tornado activity.

For Shepherd in particular, there’s no place like home when considering the geographical focus of much of his meteorological research. “Science is my proverbial yellow brick road,” explained Shepherd. “It’s taken me down some fascinating paths, especially in learning more in recent years about tornado phenomena in my own backyard.”


–Gretchen Cook Anderson, NASA’s Earth Science News Team