Oklahoma tornado was widest on record
The deadly tornado near Oklahoma City last week was a record-breaking 2.6 miles (4.2 km) wide and packed winds of up to 295 mph, weather officials said.
It was the second top-of-the scale EF-5 twister in the area in 11 days, the National Weather Service said.
Last Friday's storm in El Reno, along with flooding, killed 18 people, including three storm chasers.
The other EF-5 tornado hit the nearby city of Moore on 20 May, killing 24 people and wreaking widespread damage.
Friday's massive twister avoided highly populated areas near the Oklahoma state capital, sparing lives.
"If it was two more miles this way, it would have wiped out all of downtown, almost every one of our subdivisions and almost all of our businesses," El Reno Mayor Matt White said.
William Hooke, of the American Meteorological Society, says it is only "a matter of time" before such a tornado hits a major urban centre.
"You lay that path over Oklahoma City, and you have devastation of biblical proportions," Mr Hooke told the Associated Press news agency.