Monday's monster Oklahoma tornado traced nearly the same path and "was at least in the same league" as the historic May 3, 1999, twister that was the most powerful tornado ever recorded, weather officials said.
[Update, 5:29 p.m. May 20: Oklahoma authorities said at least 37 people were killed in the tornado, and that the number would rise. Hospitals were treating scores of casualties, including children.]
The tornado that cut through the Oklahoma City suburb of Moore was rated at least an EF4, the second highest rating, and clocked winds of about 200 mph. Once more measurements are taken, the storm has the potential to be upgraded, weather officials said.
Neighborhoods have been flattened, a search and rescue operation is ongoing at a devastated elementary school and piles of debris can be seen across the area.
At Plaza Towers Elementary School, the storm tore off the roof, knocked down walls and turned the playground into a mass of twisted plastic and metal, according to the Associated Press.
Forecasters say the threat of more twisters in the area is dissipating, but it's not over.
"It's decreased , but the night is young," said Patrick Marsh, a meteorologist with the National Weather Service in Oklahoma City.
A cold front is pushing the violent weather toward Dallas and Little Rock, cities that should begin to see severe weather Tuesday, he said.
Forecasters at the National Weather Service had been tracking the incoming storm for days and had affixed a "moderate risk" assessment to the system.
The storm was created by a warm humid air mass that stalled in the central plains. That hot air was propelled upward by the cold front, where it was spun into the upper atmosphere in a vortex of swirling wind.
These so-called super-cell thunderstorms -- often accompanied by pelting hail -- are not uncommon. And they spawn powerful, violent weather.
"We are getting to the upper end of the tornado spectrum," Marsh said.
Marsh said wind speeds created by tornadoes are difficult to quantify because the wind "tends to destroy measurement devices." One way meteorologists assign categories to tornadoes is to look at photographs of damaged buildings.