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BIRMINGHAM, Ala (WIAT-TV) - The El Reno tornado that struck just outside of Oklahoma City on May 31 earlier this year was memorable for many reasons. It developed rapidly and moved erratically; factors that may have contributed to the deaths of legendary storm chaser Tim Samaras and his team, which included his son. In all, eight people lost their lives, several trapped in cars. The storm spawned several twisters that seemed to rotate around a massive meso-cyclone. It was documented by several chasers who survived and two portable doppler radars captured astonishing images from a close range.
The National Weather Service initially rated this as an EF-3 tornado because of the observed collapse of several metal buildings. Those winds are estimated between 136 and 165 mph. However, in light of the radar data which revealed estimated winds over 250 mph, the tornado was upgraded to EF-5. That seemed logical based on what many saw that day.
Then, something odd happened over this Labor Day weekend. Quietly, word leaked that the storm had been downgraded back to EF-3. The rationale from the NWS is that while doppler radar may have measured those higher winds, the damage wasn’t consistent with those speeds. Part of the reason for that may have been the rural location of the storm; those high winds didn’t have anything to destroy. The weather world is all abuzz about it because many can’t fathom this strict adherence to the “letter of the law”; claiming it dilutes the significance of the storm.
The mere mention of the word “tornado” strikes fear and terror in most. But not all twisters are the same and can produce different kinds of destruction. To help estimate the damage, the National Weather Service rates tornadoes on a scale from EF0 to EF5, the “Enhanced Fujita Scale”. This method, first developed by renowned researcher Dr. Ted Fujita, looks at the damage and estimates the wind speed that caused it. In 2007, the scale was updated to account for the type of structure that was damaged taking account different construction types. For example, a 90 mph wind might destroy a shed, but only lightly damage the roof of a well-constructed home.
Here’s the scale:
EF0: 65 – 85 mph
EF1: 86-110 mph
EF2: 111-135 mph
EF3: 136-165 mph
EF4: 166-200 mph
EF5: over 200 mph
So, the bottom line is, should estimated winds be included in determining a tornadoes strength? Here’s what Jim Stefkovich, the Meteorologist in Charge of the Birmingham NWS office told me:
“The NWS is exploring whether this policy should change to allow the use of experimental radar data in future EF rating determinations. During the next few months, the EF-Scale Steering Committee, led by Jim LaDue, will meet to review and discuss the EF-Scale and current policy on how NWS determines storm ratings. The committee may then decide to propose changes to the policy.
The NWS will lead an EF-Scale Rating Open Forum at the annual American Meteorological Society meeting in Atlanta, GA, in February 2014. Should the EF-Scale Steering Committee propose changes to the policy, forum attendees will have an opportunity to provide feedback. Any recommendations that would support the development of updated standards for rating tornadoes would then be incorporated into NWS policy.”