I can’t talk about science right now without talking about the tornadoes that have ripped across the South and Midwest this year – most recently in Alabama, Missouri and Oklahoma. Scientists still find it extremely difficult to predict when and where a tornado might touch down, and even though there are a specific set of conditions required for a tornado to form, it is still unclear why some supercell thunderstorms form tornadoes and others do not. And, unlike hurricanes, it’s also incredibly difficult to predict what a tornado season might bring – while scientists can predict how many hurricanes a season might bring, and how severe each hurricane could be, experts are at a loss when it comes to predicting the strength and severity of a tornado season.
For those of you that don’t know how a tornado is formed, NPR has a great graphic representation, but in very basic terms, tornadoes are formed from supercell thunderstorms under certain conditions. In tornado alley, for example, warm, moist air comes up from the Gulf of Mexico and meets with cold air traveling down from Canada. When the air meets, an updraft is formed and a thunderstorm is born. Sometimes, due to winds at various altitudes and different directions, a spinning vortex of air is created in the middle and voilà, you have a tornado.
The severity of a tornado in the U.S. is based on the Enhanced Fujita Scale. The scale goes from EF-0 (winds of 65–85 mph, light damage, branches pulled off trees) to EF-5 (winds over 200 mph, incredible damage, houses ripped from foundations). The tornado that hit Joplin, Missouri on May 23 was an EF-5. The picture below shows before (right) and after (left) the Joplin tornado. You can also easily see the tornado’s path – it was nearly a mile wide. For more before and after images, head over to NPR’S The Picture Show.
Even if you don’t live in tornado alley, it’s always good to know how to survive a tornado. The best place to hide is underground, in a basement or shelter. If you can’t get underground, hide in the most interior room in your house, and make sure you stay away from any windows. The more walls between you and the tornado, the better. Tornadoes are notoriously unpredictable as they travel – one might destroy an entire city block then skip the following block, or suddenly change direction. If you are out in the open, do not hide under a tree or under a highway overpass (which tend to act like wind tunnels). Try to get to a building, but if you cannot, lay down in a ravine or depression in the ground and cover your head with your hands. NPR has some other safety precautions here.
One of the most amazing documented survival stories from Joplin is the story of the group of people who took refuge from the tornado inside a walk-in cooler in a convenience store. In case you haven’t seen it yet the original video is below, followed by the author’s follow up tour of the damaged convenience store. Be warned – it’s actually quite disturbing even though you can’t really see anything. It’s definitely a lot scarier than Bill Paxton and Helen Hunt made it seem in Twister.