By Deborah Zabarenko, Environment Correspondent
Tornado season in the United States generally starts in March and continues through the summer months but winter tornadoes have become an almost annual occurrence, according to Harold Brooks of the National Oceanic and Atmospheric Administration.
Tornadoes that rolled through Arkansas, Alabama, Mississippi, Tennessee and Kentucky this week killed more than 50 people. Brooks said tornadoes in the southeastern United States occur in winter "roughly once a year," he said.
There were previous deadly tornado outbreaks on March 12, 2006, in Missouri and Illinois and on January 1, 1999, in Arkansas and Tennessee, Brooks said.
Tornadoes develop in warm, moist air ahead of east-moving cold fronts. There are 800 tornadoes reported in the United States in an average year, resulting in 80 deaths and over 1,500 injuries, according to the weather agency's Web site http://www.nssl.noaa.gov/edu/safety/tornadoguide.html.
Does climate change play any role in the frequency or intensity of tornadoes? Brooks said no, adding that the historical record of tornadoes is insufficient to let scientists figure out what impact, if any, climate change has.
(Editing by Bill Trott)
