DENVER — The unusually quiet tornado season of 2012 and the active first month of the new year may be a sign of things to come as global warming tightens its grip on Tornado Alley, a prominent weather official said at a national storm chasers convention Saturday.
Tornado season essentially flat-lined after an unusually busy beginning, the Weather Channel’s Greg Forbes told the crowd of about 300 chasers gathered for ChaserCon 2013.
The last big outbreak of the year occurred on April 14, which included dozens of tornadoes in Kansas — among them a mile-wide tornado that struck Oaklawn and parts of southeast Wichita.
But then Tornado Alley fell asleep. There were actually more tornadoes in Canada than the United States in July, said Forbes, the severe weather expert for the Weather Channel.
Finally, 2012 awakened in its final weeks.
December saw the largest Christmas Day outbreak on record in the Southeast, he said. January followed up with the second-largest outbreak on record for the month and an overall total that more than doubled the month’s average.
“We’re going to get more tornadoes in the winter in a warming climate mode,” Forbes said.
The Texas panhandle recorded its first-ever December tornadoes and North Carolina recorded its first-ever cold season tornadoes in January 2012, he said.
Yet “it’s pretty darn hard to show a correlation between global warming and tornadoes,” Forbes said.
For one thing, he said, early tornado statistics are so unreliable it’s easy to make the mistaken assumption that there are far more tornadoes than there used to be.
When the national weather bureau began collecting tornado statistics in the 1950s and ’60s, the totals were little more than a compilation of newspaper clippings.
“If it made the newspaper,” Forbes said, “it made the tornado database.”
That meant many tornadoes went unrecorded if they did little or no damage. Nowadays, virtually no tornado goes unnoticed.
“There’s lots of chasers out there – people sending in video,” he said.
But if 2012 is indeed a sign of things to come later in this century, Forbes said, residents can expect more strong rain events and damaging wind incidents such as derechoes.
Based on computer modeling done by a colleague, he said, Tornado Alley as we currently know it would likely become quieter, with more of the activity shifting to the north and also east of the Great Plains.
Tornadoes would much more commonly form along squall lines — as opposed to the isolated supercell thunderstorms now commonly associated with the peak of tornado season.
Of more immediate interest to the chasers gathered at the DoubleTree was the outlook for the coming season. Forbes warned them it could well be another subdued year for tornadoes.
Last year, he said, “was about as quiet as it ever gets.”
If the drought persists through the spring, the sun will bake dry soil in the Rockies, sending warm air east over Tornado Alley. That warm air aloft will serve as a “cap” on the atmosphere, he said, preventing thunderstorms from shooting into the upper atmosphere and gathering the energy to become supercells over the Great Plains.
That, by extension, impedes tornado development.
The end result would mean fewer tornadoes overall, he said, with the bulk of the action east of the Plains.