Tornadoes are a primarily North American phenomenon. The U.S. has about four times as many tornadoes as all of Europe (excluding waterspouts and if you ever lived in Nebraska, you know why). North America stretches a long way North to South and there aren’t any major east-west mountain ranges that block the flow of air all the way from Canada to Mexico, so much larger fronts can form than in areas with more mountainous regions.
The Midwest has a lot of tornadoes — as you can see from the figure at right — because the Rockies block moisture and cause the atmospheric flow to buckle. That forms low-pressure, dry areas to the east of the mountains. The Gulf of Mexico provides lots of moisture, which makes ideal conditions for tornado formation. The U.S. averages about 1,200 tornadoes per year. Most happen between 3 p.m. and 7 p.m., but they can occur at any time of the day.
How do Tornadoes Form?
Tornadoes form in boundary areas, like those between hot, dry air in the West and warm, moist air in the East. The Central Plains states experience strong storms this time of year. Those storms move East and, depending on their North/South extent, can cause storms and tornadoes throughout a wide swatch of the country.
The worst tornadoes are spawned by thunderstorms called supercells, which contain mesocyclones. ‘Meso’ means ‘mid’. A mesocyclone is a medium-sized rotating air mass and, in meteorological terms, that means from a mile to five miles across. Supercells also have very heavy rain, lots of lightening, strong winds and hail.
When it starts raining really hard, the rainfall drags air down with it toward the back of the supercell. The downdraft accelerates as it nears the ground, and drags the supercell’s mesocyclone down with it. If you see a cloud that shows any sign of rotation, that’s time to start being concerned. The mesocyclone approaches the ground, and a condensation funnel forms. The condensation in the storm is the same thing as steam forming water droplets on the lid of a pot of boiling water. The coolness of the downdraft condenses water from the air, and that forms the condensation funnel. The rear downdraft keeps moving downward, which creates a very strong wind capable of causing damage well away from the funnel cloud. A funnel is a rotating structure descending from the clouds, while a tornado is a funnel that has reached the ground. The funnel cloud can become a full-fledged tornado within minutes of the rear wind gust hitting the ground.
Tornadoes are powered by warm, moist air. The more air, the more energy the tornado has, and the tornado will keep growing as long as it has access to warm, moist air. Tornadoes with diameters of more than a mile have been reported. At some point, the cool rear downdraft will wrap around the tornado and prevent more warm air from reaching it. The vortex, deprived of energy, begins to weaken, the size decreases and the tornado can be dispersed by the straight-line winds from the storm. Don’t let the size of a tornado fool you. Even what appears to be a small tornado is capable of causing a lot of destruction due to conservation of angular momentum. When an ice skater is spinning, she spins more slowly when her arms are out, creating a larger effective diameter. When she pulls her arms in, she spins faster. A thin tornado can still feature very strong winds.
Once the original tornado is gone, it’s entirely possible for the cycle to repeat again, with a new mesocyclone descending. Tornadoes are good in that they have a limited lifespan (you won’t see three-day tornadoes, like you would a hurricane), but unlike hurricanes, we still don’t have the technology to predict where and when a tornado will pop up.
“Tornado outbreak” doesn’t have a specific scientific meaning – it mostly means a lot of tornadoes are spawned from a single storm. The worst outbreak on record was the “Super Outbreak” in April 1974. There were 148 tornadoes in 18 hours, with six being classed as F5 (the most destructive) and 24 classed as F4. About 315 people were killed in the U.S. and Canada and over 5000 people were injured. This history is one of the reasons that people are so concerned about tomorrow’s weather. The storm that is headed to Alabama passed through Texas earlier in the week and produced the largest tornado outbreak of 2010 to date – 32 tornadoes.
Tornadoes must have two fundamental ingredients: wind shear and some instability, like the aforementioned hot/cold and dry/wet condition along a front. Most of the time, you have some combination, like a little of one and a lot of the other. Meteorologists start getting worried when there is a lot of both. NOAA predictions are interesting to read, but you need a little background. There are multiple weather models because weather is fundamenteally difficult to predict. (Very much like the results of a Talladega race.) Meteorologists run several scenarios with the different models and try to figure out which one is most accurate for the particular situation. Our local meteorologist talks about ‘one model shows this and others show that, but I think the first one is right’. The closer the weather system gets to actually spawning a tornado, the more confidence we have that one or more of the models are accurate.
For every Jim Cantore you see standing out in the middle of a tornado or hurricane showing people how bad the conditions are and why no one should be outside, there are a hundred meterologists at federal agencies and TV stations poring over the output of their models, trying to figure out which model is most correct so that they can give the maximum amount of warning to the areas that are in danger. Even though we can’t pin down the location, if you are or are planning on being out at the track, take this seriously and be careful.
Some Myths Debunked
- Opening windows does nothing. Yes, the pressure may drop outside, but it is almost impossible for the pressure differential to be so great as to cause the house to “explode”. There is actually evidence that opening windows is worse in terms of damage to the house. If it’s a really serious tornado, it is going to do some damage and it is not going to care whether your windows are open. (A tornado also can’t lift up your house and deposit it in Oz, but it gave me an idea for a funny story that involves Kevin Harvick as Dorothy and the media as the Munchkins.)
- Highway overpasses are not safe places during a tornado. Steel-reinforced concrete is strong, but not stronger than a tornado. If the overpass is hit by a tornado, it can fall and anyone in the vicinity is in danger of being hit by debris. If you think about it, the area underneath an overpass basically funnels all the wind through that area, so you are in much more danger being under an overpass than you are in your house.
- No geographical feature protects you from a tornado. They go over the river and through the woods, through cities, over hills, and basically wherever they care to go. Lying in a ditch is the best thing to do if you’re outside, but it is much better not to be outside.
- Motorhomes and RVs do NOT cause tornadoes; however, you are much more likely to be injured by a tornado or high winds in a RV or motorhome than you are in a permanent structure.
- The Vortex Theory can prevent tornadoes. It cannot.
What to Do
What you SHOULD DO, especially if you are out at the racetrack:
- If you’re at home and planning on heading for the track, listen to the radio to make sure activities haven’t been delayed or cancelled because of the weather.
- Have a weather radio with fresh batteries and spares. Listen to the weather, watch it on TV, and be aware that you may need to take action on short notice.
- If you’re camping or RV’ing, have a flashlight and emergency kit that includes the basics, like bandages, antiseptic, etc.
- Make an emergency plan for your group – identify two places to meet if something happens and you are separated. One place should be near your campsite or seats and another should be a little further away, to be used if there is damage to the first area. Cell phone lines often become overloaded during emergencies, so don’t count on being able to reach each other on the phone.
- Don’t get stupid drunk. You may need to think quickly. Wait until after the storm warnings have expired to enjoy the special pleasures of Talladega.
- If you hear sirens or radio/television reports that a storm is coming, get into a permanent structure if at all capable. My guess is that the safest place at Talladega if you’re out camping is in a ground-floor bathroom in a concrete structure. Like being on an airplane, identify two such structure because there are likely to be a lot of people with the same idea you have. If you can get underneath something heavy, like a sturdy table, a workbench, or anything else that would protect your head from falling debris, that’s even better.
- Remember that NASCAR fans share a unique bond that makes us more like family than strangers, even if we’ve just met. If someone needs help, help them — even if they are wearing a xx t-shirt (where xx is your least favorite driver’s car number).
I do not envy the folks at Talladega trying to guess the best way to proceed. I was at Richmond two years ago when there was a hurricane. The race was cancelled the day before. It was beautiful in Richmond that Sunday, but there was a lot of damage on most of the routes leading to the racetrack.