South's 'super tornado' outbreak may be worst ever in US history

The king of a series of massive long-track tornadoes that clobbered the South this week may have traveled in excess of 220 miles across Alabama, Georgia, and Tennessee, carrying wind speeds in excess of 200 miles per hour, all of which could make it the most powerful tornado ever recorded in the US.

The only rival so far is the 1925 "Tri-State Tornado" that ripped through the upper Midwest on a 219 mile track, killing over 700 people. That tornado traveled at up to 73 miles per hour. Wednesday's Tuscaloosa super tornado may not have reached those land speeds, but, taken in combination with up to a dozen other potential EF-5 tornadoes spawned from Wednesday's storms, several aspects of the Tuscaloosa twister and the outbreak as a whole may be unprecedented.

Some 211 tornadoes were reported within a few hours' span on Wednesday, including a series of so-called long-track twisters that raked across six states, killing at least 350. Among that twister outbreak, the Tuscaloosa tornado is likely to have resulted in most of Alabama's 228 reported casualties as it tracked to the northeast after hitting Tuscaloosa, crushing neighborhoods like Pleasant Grove in Birmingham and continuing into Cherokee County, where it flattened homes near Spring Garden. Debris from Tuscaloosa was recovered in Rome, Ga., 178 miles away.

IN PICTURES: Alabama tornadoes

It's still not clear to tornado experts whether the same tornado traveled the entire distance or whether it dissipated and reformed along the path as separate twisters as it bounded from the central Alabama flats into the Appalachian foothills.

Thanks to improved forecasting and more precise warning systems, tornadoes' annual casualty toll has steadily decreased, averaging 62 a year between 2000 and 2009. But given those improvements since 1925, when most forecasting was done by eye and barometer, the storm's high death toll is an indicator of both its track, which took it over highly populated areas, as well as its ferocity.

"The truth is, even if you did everything you were supposed to do, unless you were in an underground bunker, you weren't going to survive," James Spann of the ABC affiliate in Birmingham, Ala., told The New York Times.

EF-5 tornadoes on their own are rare, occurring, on average, once every four years. So far, only one tornado from last week – one that hit Smithville, Miss. – has been classified as an EF-5, becoming the first time such a high-magnitude twister has hit the Magnolia State. But tornado experts expect more such classifications as officials assess storm strengths based on debris field forensics. As measured by a tornado ranking system, F4 and F5 tornadoes are the most intense, rated by the damage a tornado causes after passing over a manmade structure.

The sheer numbers of twisters from one storm front may also be unprecedented. If the estimated number of tornadoes – 211 – holds fast, it would far outpace the previous modern record: the 148 confirmed tornadoes spawned during the "Super Tornado Outbreak" of 1974, which killed 308 people across the US and Canada.

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