Tornado Alley is a non-scientific term used to describe an area in the US where tornadoes are frequent. By some estimates, as many as 25% of the world’s tornadoes form in Tornado Alley. Coined by two US Air Force meteorologists (Maj Ernest Fawbush & Captain Robert Miller) to describe their study of severe weather in 1952, the name is also synonymous with Tornado Belt and Tornado Valley. Not to add confusion, Canada also sports a region known as Tornado Alley. More on that below.
What is a Tornado?
Tornadoes are rapidly rotating columns of air. Wind speeds vary from 100 miles per hour (160 Km/hour) to as high as 300 mph (480 Km/hour). Tornados come in a wide variety of sizes. The smallest might be no more than 10 feet (3 meters) on the ground. A large tornado can be more than a mile (1.6 Km) wide. A May 2013 tornado in Oklahoma was measured at 2.6 miles (4.2 Km) wide. Tornado tracks also vary greatly and have been reported from less than 10 feet (3 meters) to many miles. A 1925 tornado maintained contact with the ground for 219 miles (350 Km) as it crossed Missouri, Illinois, and Indiana. The average US tornado travels ~5 miles (8 Km) along the ground before dissipating. While not caused by the Coriolis Effect, tornadoes in the northern hemisphere rotate counterclockwise and those in the southern spin clockwise.
What Causes a Tornado?
Tornadoes form from the interaction between rising warm air interacting with a storm’s moist downdraft. This creates lower pressure at the bottom of the funnel, drawing in more air and accelerating the vortex toward the ground. Once it hits the ground, the funnel becomes a tornado. After contact with the ground, the cool downdraft wraps around the tornado, squeezing off the supply of warm air. Eventually, it shuts down the supply completely and the tornado begins to dissipate. From touchdown to dissipation can last from a few minutes to more than an hour.
Why Does Tornado Alley Exist?
As noted above, tornadoes require the interaction of cool, dry air with warm, humid air. In the Central US, tropical air from the Gulf of Mexico (or America if you’re so inclined) often meets cold, dry air from the Arctic. The interactions of these air masses create powerful thunderstorms, which in turn spawn tornadoes. This same process also plays out in the Canadian plains provinces and in eastern Canada which is close to the warm water of the Gulf Stream.
Our Featured Maps of the US and Canadian Tornado Alleys courtesy of Wikimedia.
As always thanks for reading.
Armen
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