The tornado was a top-of-the-scale EF5, one of two EF5 twisters to strike the area in less than two weeks.
Nineteen people died in that storm and flooding, including three "storm-chasers." Victims included six children and 13 adults. Six victims remained unidentified Tuesday.
On May 20, the town of Moore was struck by an EF5 tornado, killing 24 people. In 1999, Moore was hit by an EF5 tornado that reached 302 mph, the strongest winds ever measured on Earth.
The storm's 2.6-mile-wide path surpassed a record set in 2004 in Hallam, Neb. And it would have made the storm hard to recognize up close, Smith said.
The twister marched through the countryside between El Reno and Union City, a region of largely 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.
"A 2.5-mile wide tornado would not look like a tornado to a lot of people," said Rick Smith, chief warning coordination meteorologist for the weather service's office in Norman, explaining that the twister would not have a tapered funnel and would instead resemble a dark cloud hanging below the horizon.
Greg Carbin, a meteorologist for the National Oceanic and Atmospheric Administration's Storm Prediction Center in Norman, said May in Oklahoma is a time of weather transition, offering the perfect fuel for violent thunderstorms that can produce tornadoes - a combination of warm, moist air combined with cooler jet stream energy that causes massive instability in the atmosphere.
Tornadoes are rated by the NWS using the Fujita (F) and Enhanced Fujita (EF) damage scales.
The Associated Press contributed to this report.
