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Tornado: 40 minutes of hell

The deadly aim of the Oklahoma twister.

Most tornadoes -- think of the smaller ones that touch down around here on occasion, are evanescent -- lasting fewer than 10 minutes.

So for those of in the Midatlantic and Northeast, it may be difficult to envision one that survives a full 40 minutes and packs winds of up 200 m.p.h. winds, or perhaps higher.

But aside from the sheer power and duration of the unimaginably destructive Oklahoma twister, evidently it was unusual in another critical and tragic way: It happened to rip through a populated area.

In the storm-survey update posted just before 1 p.m. our time, the National Weather Service reported that it traveled a total of 17 miles and was at least and EF-4 on the Enhanced Fujita scale, a rating that accommodates a gust up to 200 m.p.h.

Storm advisories were issued as early as Friday, and a tornado warning was posted at 2:40 p.m., according to the National Weather Service. The wister touched down at 2:56 p.m.

A 17-mile path would be close to the median path for an EF-4, said Harold Brooks, lead scientist at the government's Storm Prediction Center, in Norman, Okla., about 10 or 15 miles southeast of the tornadic path, incidentally.

During the horrific April 2011 outbreak in the South blamed for killing over 300, 15 "violent" tornadoes - EF-4s and 5s, were documented. Of those, eight traveled over 50 miles.

But even in Tornado Alley, the Great Plains corridor that is far and away the world's busiest tornado zone, the likelihood of a strong tornado hitting a populated area is small.

Brooks has computed that the odds of even a moderate tornado's touching down in the heart of
Tornado Alley at a given point in any one year are about one in 5,000. The odds of violent tornadoes' doing so are four times greater.

Unfortunately, it does happen -- a monster tornado tracked through Moore on May 3, 1999 -- and when it does, human beings and their buildings are greatly overmatched.

An EF-4 is capable of incredible damage.

Consider that the nation's Storm Prediction Center, itself, the national firehourse for tornado warnings, isn't designed to withstand winds over 165 m.p.h.