Width of second Oklahoma tornado was widest on U.S. record

A tornado forms near Banner Road and Praire Circle in El Reno, Okla. on Friday, May 31, 2013. (AP / Alonzo Adams)

NORMAN, Okla. -- The deadly tornado that struck near Oklahoma City late last week had a record-breaking width of 2.6 miles (4 kilometres) and was the second top-of-the-scale EF5 twister to hit the area in less than two weeks, the National Weather Service said Tuesday.

Friday's massive tornado avoided highly populated areas, and forecasters said that likely saved lives.

The weather service initially rated the tornado as an EF3, but it upgraded the ranking after surveying damage from the twister, which along with subsequent flooding killed 19 people, including three professional storm chasers. The weather service determined that the storm had winds reaching 295 mph (474 kph).

Oklahoma City area has seen two of the extremely rare EF5 tornadoes in only 11 days. The other hit the suburb of Moore on May 20, killing 24 people and causing widespread damage. In 1999, Moore was hit by another EF5 with the strongest winds ever measured on Earth: 302 mph (486 kph).

William Hooke, a senior policy fellow with the American Meteorological Society, said the continued expansion of U.S. cities in the most tornado-prone areas makes it only a matter of time before one hits a heavily populated area.

"You dodged a bullet," Hooke said. "You lay that path over Oklahoma City, and you have devastation of biblical proportions.

"It's only a matter of time."

When the winds were at their most powerful Friday, no structures were nearby, said chief warning co-ordination meteorologist Rick Smith with the weather service.

"Any house would have been completely swept clean on the foundation. That's just my speculation," Smith said. "We're looking at extremes ... in the rare EF5 category. This in the super rare category because we don't deal with things like this often."

Smith said the storm's wide path would have made it hard to recognize up close.

"A two and a half mile wide tornado would not look like a tornado to a lot of people," Smith said.