That mammoth tornado near El Reno, Okla. — the one that outsized the Hallam, Neb. tornado for widest ever — may not retain its EF5 rating.
The National Weather Service continues to review whether the El Reno tornado did indeed hit EF5 status, according to the Tulsa World. The newspaper participated Friday in a briefing held by National Weather Service officials and the Federal Alliance for Safe Homes.
Originally, based on visible damage, the El Reno tornado had been rated an EF3 by the National Weather Service. Winds with an EF3 blow at an estimated 136 to 165 mph.
Then came word that researchers tracking the tornado with mobile radar had clocked ground level winds in excess of 295 mph. That would classify the tornado as a high-end EF5. Tornadoes with wind speeds in excess of 200 mph are rated EF5.
The question of wind speed is no small matter. It has real-world implications for public safety.
Currently the Federal Emergency Management Agency advises that tornado shelters be able to withstand winds of 250 mph.
That's because researchers have believed the maximum ground-level wind speeds from a tornado are slightly higher than 200 mph, said Ernest Kiesling, an expert in tornado shelters and researcher at Texas Tech University. Texas Tech is the premier institute studying tornado damage and shelters.
As a consequence, the university and FEMA recommend that tornado shelters include a margin of safety and be able to withstand 250 mph winds.
Validating a ground-level wind speed approaching or exceeding 300 mph would raise questions about the robustness of that standard.
What bothers people at Texas Tech is that this is the kind of report that discourages people from building any type of aboveground shelter. Only 1 percent to 2 percent of tornadoes reach EF5 status, and most barely edge above 200 mph, Kiesling said.
FEMA-type shelters save lives. Too many people believe the falsehood that an EF5 tornado cannot be survived in an aboveground shelter, Kiesling said.
“That causes my blood to curdle — it's an absolutely false statement and it's very, very unfair to the public,” he said.
Until the El Reno tornado, no one had ever recorded such wind speeds.
Researcher Josh Wurman is noted for the 318-mph winds that he recorded in the 1999 Moore, Okla., tornado. But those wind readings were taken high aboveground. Friction from contact with the ground slows down tornadic winds.
The El Reno tornado was documented at 2.6 miles wide, making it the widest ever recorded. Before El Reno, the 2004 Hallam tornado was the widest ever recorded, 2.5 miles.
Here's the Tulsa World news story.