OKLAHOMA CITY — The deadly tornado that struck near Oklahoma City last week had a record-breaking width of 2.6 miles 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.

The weather service initially rated the tornado that hit El Reno Friday as an EF3, but the agency upgraded the ranking after surveying damage, and determined that the storm packed winds reaching 295 mph. Eighteen people died in the storm, including three storm chasers, and its subsequent flooding.

Deep in the heart of Tornado Alley, the Oklahoma City area also saw an EF5 tornado on May 20. That one raked Moore, a suburb 25 miles away from El Reno, and killed 24 people. In 1999 Moore was hit by another EF5 with the strongest winds ever measured on earth, 302 mph.

Friday’s tornado avoided highly populated metro areas, a fact forecasters said likely saved lives. Winds were at their most powerful in areas devoid of structures, said Rick Smith, chief warning coordination meteorologist for the weather service’s office in Norman.

“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.”

The stretch between El Reno and Union City that the twister spun through is mostly rural farm and grazing land. Most of the destruction came toward the end of the tornado’s 16.2-mile path along Interstate 40, where several motorists were killed when their vehicles were tossed around.

Like many Midwestern cities, the Oklahoma City metropolitan area continues to expand thanks to the suburbs, but the rapid growth hasn’t quite reached as far west as where Friday’s tornado tracked.

William Hooke, a senior policy fellow of the American Meteorological Society, said the continued expansion of 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.”