The Oklahoma tornado was a tragic event, but the reasons behind that terrible storm lie in the laws of physics and meteorology.
A tornado consists of a rapidly-rotating column of air caught between a thunderstorm and the ground. They form when moist, warm air runs into a cool, dry region of air. As warm air rises, an updraft is created. This can be buffeted by winds, constantly changing direction and increasing in velocity. The characteristic whirlpool motion seen in these storms begins to form and a funnel cloud develops. As the height of the system increases, cool air is brought from the jet stream above, adding energy into the system. The lengthening air system finally touches ground, and a tornado is formed.
On May 20 at 2:40 p.m., the first tornado warning was issued for areas including the Oklahoma City suburb of Moore. Radar suggested touchdown at 2:52 p.m. and the first eyewitness reports came in four minutes later. The deadly wind system lasted nearly an hour before dissipating at 3:36.
"You could actually feel the vibration from the tornado itself as it was approaching," Lauren Hill, a storm chaser who helped to record video of the deadly twister, said.
Oklahoma is prone to tornadoes, with an average of over 60 violent tornadoes recorded in the state each year. Part of the reason for this is its geography - the state receives a large amount of both warm, moist air from the Gulf of Mexico as well as drier, cooler air from the Rocky Range to its west and north. This is the fourth time that Moore has been struck by a severe tornado in the last 15 years. The three previous events were in 1999, 2003, and 2010.
The most severe tornadoes can exhibit winds over 250 miles an hour. One out of every thousand thunderstorms is powerful enough to be deemed a supercell, and of these, around 20% develop tornadoes.
This may not be the end of dangerous weather for the area, as the storms will continue through at least the evening of May 21.
Meteorologist Dave Hennen of KTVT in Fort Worth predicts, "The primary tornado threat will be from mid-afternoon to late evening hours in that region."