Oklahoma leads the world in tornadoes

• More EF5 tornadoes have hit Oklahoma than any other state
• Clash of warm air from Gulf and cold air from Rockies combine with deadly results
• May 31 tornado was widest ever

Oklahoma may be "OK" according to the state's license plates, but for tornadoes, its more than OK — it's the world champ.

"Central Oklahoma has more tornadoes per square mile than anywhere on Earth," says AccuWeather meteorologist Mike Smith.

Over the last two weeks of May, two rare EF5 tornadoes, the strongest on the 0-to-5 Enhanced Fujita Scale of Tornado Intensity, tore savage paths through the Sooner State, killing dozens of people. The one that hit May 31 was 2.6 miles wide, the widest ever recorded.

In fact, of all the F5 or EF5 tornadoes that have hit the USA since 1950, Oklahoma has been hit by eight, more than any other state. An EF5 tornado is any tornado that has wind speeds of 200 mph or higher. The Enhanced Fujita scale replaced the Fujita scale (noted with "F" ratings) in 2007.

Last month's tornadoes tore through populated areas near Oklahoma City —"probably the largest, most tornado-prone urban area in the world," according to weather historian Christopher Burt in his book Extreme Weather.

Why is this? Why is the Sooner State so prone to deadly and devastating twisters? Unfortunately for Oklahomans, it's a dangerous and unlucky combination of meteorology, timing, topography and geography.

"The ingredients come together in our part of the world so often because of the proximity of the Gulf and Rockies," says research meteorologist Harold Brooks of the National Severe Storms Laboratory in Norman, Okla

Oklahoma provides a fertile breeding ground for tornadoes because of the clash between the warm, moist air from the Gulf and cold air from the Rockies and Canada: One of the main keys to tornado formation, Smith says, is "a large temperature spread over a short distance."

"Water holds its heat more than land or air," Smith says. "So Oklahoma's proximity to the Gulf of Mexico means there is a source of very warm, moist air. As cold air comes from Canada, you can get temperatures of 80 degrees in the body of the state while it is in the 20s in the Panhandle." He says this provide the power to fuel severe thunderstorms.

The time of year when most big Oklahoma tornadoes occur — May — is also key, according to Greg Carbin, warning coordination meteorologist at the Storm Prediction Center. May is a transition season, which has vestiges of winter cold and of the upcoming heat from summer. "It sets up these incredible contrast between air masses," he says.

Other factors include strong winds at high levels of the atmosphere along with a supply of dry air nearby, both of which Oklahoma has, Smith says: "The dry air from the New Mexico desert is just about in the perfect place to form a 'dry line,' which is often in Oklahoma."

Dry air is also crucial to tornado formation, Smith says, so the storm doesn't get overloaded with rain and hail, which can cause it to collapse before it gets a chance to form a tornado.

Oklahomans can likely breathe a sigh of relief after enduring the state's deadliest month for tornadoes in 14 years: The worst of the severe storm season has likely passed, as tornadoes usually form a bit farther to the north in June.