Spring is always a bad time for tornadoes in the Midwest. I remember the devastating storm that hit Xenia, Ohio in the 1970s. Which is why a feature in the May 19th edition of EarthSky News caught my eye. I’m copying the basic information here. The complete article can be found at http://earthsky.org/earth/4-basic-questions-about-tornadoes? The photo is from the article.
1. What are the peak months for tornadoes in the U.S.?
The highest average number of U.S. tornadoes per month is in May, followed by June. May is the time when the two ingredients that are required – very unstable air and strong vertical wind shear – are most common. That being said, we’re now seeing a trend of tornadoes breaking out earlier in spring, such as April or even March.
2. What U.S. states/regions have the most tornadoes, and why?
The Great Plains is where the most tornadoes occur; the region is often referred to as Tornado Alley. It’s an ideal location due to warm, humid air flowing northward from the Gulf of Mexico at low levels, and cold, dry air coming down from Canada at upper levels, producing very unstable air. Beyond the Great Plains, tornadoes occurring over the southeastern U.S. have recently attracted scientists’ interest.
3. Are there tornadoes in countries other than the U.S.?
Tornadoes are typical in the mid-latitudes, between 30 and 50 degrees north and south. Countries that experience tornadoes include Bangladesh, Japan, Australia, New Zealand, China, South Africa, Argentina and many nations in Europe.
4. What are we learning about how and when tornadoes form?
Tornadoes usually occur in association with particular types of severe storms, such as supercells and squall lines, called tornado parental storms. But not all these parental storms generate tornadoes. Tornadogenesis, as the formation of tornadoes is called, remains the “holy grail” of tornado research. Recent work suggests that the temperature of the outflow air from the parent thunderstorm could play a critical role. There is a lot we don’t yet understand, including the circumstances that produce tornado outbreaks.