OK

Tornado
Devstation in Moore, OK, courtesy of Jeff Masters at the WeatherUnderground. Click for more expert storm info & images.

There's been some confusing numbers thrown out on the rating of the tornadoes that devastated Oklahoma yesterday. Earlier Tuesday some outlets reported one was an F4, Tuesday afternoon I heard at least one news anchor call it an F5. This probably arises from two closely related but different intensity rating systems. The scale used by storm meteorlogists today is the Enhanced Fujita Scale, that's why you see the "EF" designation popping up. The older scale popularized by movies like Twister is the Fujita Scale. The original Fujita scale defines an F5 tornado as winds greater than 260 MPH, but the EF scale cuts off at 200 MPH. The change in scales has to do with a better understanding of the physics of wind energy. In laymen's terms, once wind velocity gets above ~ 200 MPH the destruction is so devastating it's difficult to distinguish finer dividing lines just beyond that without expert analysis.

It is a certainty the tornado that struck Moore, Oklahoma, was an EF5. When you see cars tossed like they are above, on top of a shredded steel-reinforced cinder-block storm-rated structure, that's about as bad as it gets. If surface winds in a hurricane were to get as strong as they did yesterday in Moore, we would have to extend the Saffir-Simpson Hurricane Intensity Scale two more notches, to at least Category Seven. The National Weather Service will examine the tornado tracks and debris field to try to estimate the max winds. It remains to be seen if there's evidence for speeds above the older 261 MPH threshold. But the question is really just academic at this point.

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