Sunday, February 24, 2008
News

Too early for twisters?

.

Randi Schutt looks through family photos she found while searching through the rubble after a tornado ripped through Arkansas on Feb. 6.

CREDIT: Rick Gershon/Getty Images

By Mark Woolsey
    
When severe thunderstorms and threatened tornadoes ripped across metro Atlanta on Sunday, Feb. 17, some people showed utter disregard. Others huddled in hallways or basements with flashlight, portable radio and water bottle at hand. We all know the drill. And fortunately, the pounding storms resulted in nothing more than a few roofs ripped loose and other scattered damage
      
But isn’t it a little early for Atlanta to be getting these twisters—what experts call supercell thunderstorms?
      
The answer, according to meteorologists, is yes, this is quite unusual—although not entirely unprecedented. But pinning down why the South has been racked by severe storms and tornadoes in February is tough.
      
Check both the skies and the stats, and it’s been a strangely busy month: The Super Tuesday tornado outbreak produced a swath of storms from Arkansas through Tennessee up into the Ohio Valley and killed 58 people. Even Feb. 17’s round of nastiness, although more typical in that it originated nearer the Gulf Coast, was displaced.

It was “about a third of a state north from usual,” says Greg Forbes, a severe weather expert for the Atlanta-based Weather Channel.
     
By Forbes’ careful count, at least 114 tornadoes were confirmed by Feb. 20, as compared to an average of 28 during the same time period over the previous 10 years.

Almost 60 of those swirled from the sky Feb. 5-6, as a huge upper storm system and cold front sliding into the lower 48 out of Alaska drew on Gulf moisture, bringing warm and unstable air well north of normal. Memphis, for example, hit a humid 79 degrees just before powerful tornadoes erupted there. Combine unseasonably warm weather with the right upper-and-lower weather patterns and the right wind shear, and the atmosphere was primed for twisters.
   
Greg Carbin, warning coordination meteorologist for the National Weather Service’s Storm Prediction Center (SPC) in Oklahoma, says Super Tuesday’s setup of warm moist air and severe weather to the south, with powerful winter storms in the plains, is a “transition season” event from winter to spring that we usually see in late March—not late February. 

Are this winter’s events related to the once-every-few years La Nina weather pattern, or to the growing body of evidence supporting global warming?
    
La Nina, says Carbin, is “a global pattern that affects jet stream systems in very large ways. This is very small-scale.”
     
The overarching problem, he says, is that SPC’s official severe weather/tornado database dates only from 1950, and even some of the data since is suspect.
   
“If we had about 200 years of accurate climatology with regards to severe weather, we might be able to say something is going on” in terms of long-term global warming, he says.
      
It’s that lack of a database, plus some well-documented historical trends, that make Jim St. John skeptical. A meteorology research scientist at Georgia Tech’s School of Earth and Atmospheric Sciences, St. John says that when the global warming theory emerged, the idea was that its most pronounced effect would be to warm polar regions in the winter. If that’s the case, warming the poles and not so much the tropics would theoretically reduce the temperature difference between the two, making weather systems less strong. The atmosphere is not well understood even today, he explains. There may be as-yet-undiscovered feedback mechanisms that could either counteract or accelerate perceived trends such as a global warming.       
     
The Georgia Tech scientist stresses February’s tornado swarm was not without precedent. He points to a February 2000 tornado event in Southwest Georgia that killed nearly 20 people and injured 100 more. The biggest batch of tornados on record, he notes, happened back in 1974—before global warming notions gained traction.
    
“I am kind of skeptical when somebody comes out and says we can attribute this or that to global warming, but it’s possible,” he says. “Every time we have a question about something in the atmosphere, we say ‘if we can just get the data, we’ll have the answer.’ Then we get the data and analyze it and we realize we don’t even know the question in the first place.” SP