Good Question: Why Is This Tornado Season So Deadly?

By Jason DeRusha, WCCO-TV

MINNEAPOLIS (WCCO) — It’s only May and 2011 is already a year for the history books as tornadoes have killed more Americans this spring than in any other.

So that got Debbie in Maple Grove, Minn., wanting to know: Why has it been such a deadly season for tornadoes?

Part of the answer has to do with how many tornadoes there have been in the United States. So far, in April and May, the U.S. has seen more tornadoes than it usually sees in a year. In other words: the more tornadoes there are, the greater chance there is for disaster.

WCCO-TV meteorologist Mike Fairbourne has been tracking tornadoes for decades. He says the jet stream has been a little more chaotic than usual.

He explained that ripples in the jet stream import moist, unstable air from the south that meets cool, drier air from the north.

“And it’s the interaction of both air masses that actually creates the severe weather,” Fairbourne said.

However, no one knows why the jet stream has been so crazy this year.

The Gulf of Mexico is two degrees warmer than normal, but the wind shear in the atmosphere is the same.

To answer the question as to why the tornadoes are so deadly, that has to do with people not having basements and tornadoes hitting populated areas. For instance, if the deadly tornado that killed 139 people in Joplin, Mo., hit five miles north, only 10 people would have died.

Some have suggested that global warming might be a factor in this spring’s crazy weather, but Fairbourne doesn’t think that’s the case.

“[Global warming] has been the assumption: a warmer earth would create more evaporation, more instability in the atmosphere, but i think it’s a little bit of a stretch,” Fairbourne said.

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