‘Tornado alley’ appears to shift east
ST. LOUIS — Few people expect tornadoes in December, let alone one strong enough to collapse the 11-inch-thick concrete walls of a sprawling, new Amazon warehouse.
But the EF3 tornado that wrecked the facility near Edwardsville, Illinois, last month — one of several twisters that caused widespread damage in six states and more than 90 deaths — could be a sign of things to come.
While most people associate intense tornado outbreaks with spring, weather experts say both the timing and location may be changing.
Two decades ago, December tornadoes — if they occurred — plowed through fields and homes from eastern Texas to northern Florida, according to data from the National Oceanic and Atmospheric Administration, or NOAA. At that time, fewer storms occurred overall, and even fewer hit the nation’s traditional “tornado alley” — Kansas, Nebraska, Oklahoma and Texas. Recent unseasonable twisters tend to touch down in Mississippi, Alabama, Arkansas, Tennessee, Missouri, Illinois and Kentucky.
Scientists and those who study the phenomena agree that tornado outbreaks are moving east.
“Research has identified evidence of a ‘Dixie Alley,’ which represents an eastward extension of the traditional ‘Tornado Alley’ in the central Great Plains,” wrote Harold Brooks in a 2018 study on tornado spatial trends. Brooks studies tornadoes in NOAA’s National Severe Storms Laboratory, and said St. Louis has one of the most remarkable tornado histories of any place in the country.
The most recent complete decade of data available from NOAA, 2010 through 2019, shows 221 December tornadoes rated at the Enhanced Fujita scale of 1 or higher occurred in the U.S., compared with 143 from 2000 to 2009, and just 78 during the 1990s. The majority of December tornadoes were rated at EF2 or lower, meaning weaker storms, but the percentage of strong or violent tornadoes increased to 10% from 4% between the past two decades.
And, in MidwesternSoutheastern states, excluding Kansas, Oklahoma and Texas — also known as “tornado alley” — December tornadoes increased to 189 twisters, up 78% from 106.