Tornado records from Nebraska, Kansas, Oklahoma, and northern Texas – an area of high tornado activity dubbed Tornado Alley — show that peak tornado activity is starting and ending earlier than it did 60 years ago. That’s according to a new study published in Geophysical Research Letters on September 10, 2014.
Peak tornado activity typically occurs in the region from early May to early July. It has moved an average of seven days earlier in the year, over the past six decades. The study’s authors observed the shift in tornado activity for all categories of tornadoes that occurred in the region from 1954 to 2009.
Additional, more-selective analyses by the authors show that for some states in the region, and for stronger tornadoes, the season has advanced an average of 14 days compared to 1954. John Long, a research scientist in the Department of Land Resources and Environmental Sciences at Montana State University in Bozeman, Montana, and lead author of the new study, said:
If we take Nebraska out [of the data], it is nearly a two-week shift earlier.
Greg Carbin, the warning coordination meteorologist at the Storm Prediction Center in Norman, Oklahoma, who was not involved in the new study, said:
From a public safety perspective, if this trend (of an earlier tornado season) is indeed occurring, then people need to begin preparing for severe weather earlier in the year.
The scientists said it was difficult to pinpoint a cause for the shift in tornado activity. Records of tornado activity in the U.S. only date back to the 1950s, making it difficult to study changing trends in tornado activity. Furthermore, tornadoes can be influenced by many regional factors, including topography of the land and areas where cooler air meets warm, subtropical air, making it difficult to attribute the shift in the tornado season to any one factor, Carbin said, but he added that a warmer climate might play a role:
If winters are not as cold, or if spring times are warmer, the location of the jet stream is most likely displaced north of where it has been in the past.
This would cause tornado activity to shift earlier in the year, as is seen in the new study, Carbin said.