Tornado followed path of 1999 storm
The monster tornado in suburban Oklahoma City loosely followed the path of a killer twister that slammed the region in May 1999.
The National Weather Service estimated that the storm that struck Moore on Monday had wind speeds of up to 200mph and was at least half a mile wide. The 1999 storm had winds clocked at 300mph, according to the weather service website, and it destroyed or damaged more than 8,000 homes, killing at least two people.
Kelsey Angle, a weather service meteorologist in Kansas City, Missouri, said it was unusual for two such powerful tornadoes to track roughly the same path. The 1999 twister was part of a two-day outbreak sweeping mostly across central Oklahoma - similar to the past two days.
The weather service has tentatively classified the Moore twister's wind speeds as an EF4 on a five-point scale. Less than 1% of all tornadoes reach EF4 or EF5.
The thunderstorm developed in an area where warm moist air rose into cooler air. Winds in the area caused the storm to rotate, and that rotation promoted the development of a tornado. The most destructive and deadly tornadoes develop from rotating thunderstorms.
The biggest known tornado was nearly two and a half miles wide at its peak width, which the weather service describes as near the maximum size for a tornado. It struck Hallam, Nebraska, in May 2004.
The deadliest tornado, which struck on March 18, 1925, killed 695 people in Illinois, Missouri and Indiana.
Deaths from twisters have been declining in recent years because of improved forecasts and increased awareness by people living in tornado-prone areas, especially in smaller and rural communities.