While watering the garden one spring day, your eyes turn skyward at the sound of distant thunder. Dark clouds are building on the horizon. You turn off the hose and head inside to check the weather. As soon as you turn on the television, you're blasted with the ominous squawk of an emergency alert. "The National Weather Service has issued a tornado warning for the following counties," a voice declares through the static. Your pulse quickens as the list begins, and sure enough, you're in one of the threatened areas.
Outside, the wind picks up as you plan your next move. Where is the safest place to be? Didn't someone say to open a window? Should you even be worried about the weather forecast? The rain intensifies. You try to remember what the police officer told you in that seventh-grade assembly, but to no avail. Before you can sort it all out, things suddenly take a turn for the better: The wind and rain die down, and the sun even peeks from behind the clouds. Thankfully, your house survived with just a flicker of the lights and a few downed tree limbs in the yard. But what about next time? To prepare for the worst, you'll need to know what tornado survival tips to believe and, just as importantly, which ones to ignore.
Tornadoes, especially powerful ones, don't hit big cities very often. Between 2004 and 2014, major metropolitan areas were spared from tornadoes rated EF3 or above on the Fujita scale [source: Linkin et al.]. So is there something to the idea that urban landscapes somehow discourage tornadoes?
Unfortunately for city-dwellers, the answer is no. While it might seem logical that those tall skyscrapers are big enough to disrupt an approaching tornado, it turns out they aren't even close. Take Chicago's Willis Tower, which stands at nearly 1,500 feet (457 meters). That's less than 6 percent the height of a tornado, which can reach 5 to 10 miles (8 to 16 kilometers) into the sky. If anything, the urban landscape might actually help intensify thunderstorms into tornadoes. One study found that the heat stored in urban building materials may have actually contributed to the formation of an Atlanta twister in 2008 [source: Keim].
So why don't powerful tornadoes strike big cities more often? It's simple probability. Urban areas — even the sprawling ones — make up just a small fraction of the total land area. Chances are slim that any tornado will hit one of these densely populated places, much less the most powerful tornadoes. But it has happened in the past and will again in the future. And when it does, it could be devastating: One report suggests that a violent tornado in Chicago could inflict as much as $20 billion in damage [source: Linkin et al.]
It's understandable why motorists would seek out underpasses when a tornado threatens. There's not much else that even remotely resembles shelter when you're driving across the rural plains. But the meteorologists have spoken: Don't do it!
This tornado survival myth likely started in 1991 when a television news crew, with cameras rolling, took cover under an overpass during a very weak tornado. They survived, and the resulting footage was widely circulated. It created a surprisingly persistent misconception that was still alive and well in 2013 when the movie "Man of Steel" depicted Clark Kent's dad taking shelter from a tornado under — you guessed it — an overpass.
So what's the big deal? For one, a tornado's winds intensify with height, meaning that even the short climb up under an overpass could put you at greater risk of injury from flying debris. What's worse, the overpass's design results in a wind tunnel effect, meaning gusts actually increase in speed as they're funneled through the narrow space under the end of the bridge. These dangers were tragically demonstrated in 1999 when a powerful tornado killed three people and severely injured others who sheltered under overpasses in Oklahoma.
The best thing to do if you see a tornado while driving is to get out of the way and find the nearest shelter — but only if traffic and road options allow. If this isn't possible, take cover in a ditch or culvert and cover your head with your hands.
Some survival myths are as stubborn as the last tree standing in a tornado-ravaged forest. Such is the case with the notion that the southwest corner is the safest part of a basement when a twister strikes.
This idea gained traction way back in 1887 thanks to a book written by meteorologist named John Park Finley. In it, the U.S. Army lieutenant reasoned that tornadoes generally travel from southwest to northeast, so all the debris would be blown in that direction, endangering anyone in the northeast corner of a building. More than a century later, a surprisingly high number of people still cling to this belief, as demonstrated by a 2009 report that found nearly 60 percent of visitors to the National Weather Center understood it to be true [source: Hoekstra et al.].
There are a couple of problems with this survival strategy. Tornadoes don't always move from southwest to northeast, and even if they did, the winds don't necessarily blow in a straight line. That means debris could blow in any direction, potentially threatening all corners of the basement. So where in the cellar should you hunker down? Your best bet is under a mattress or sturdy piece of furniture — just make sure there aren't any heavy appliances above! [source: Edwards]
To understand how this myth got started, you have to know a little about atmospheric pressure, which is the force exerted on an object by the air above. It can vary depending on factors like elevation and temperature, but the standard pressure at sea level is 29.92 inches of mercury (1,013.2 hPa) [source: National Weather Service]. While the pressure can drop as low as 25.7 inches of mercury (870 hPa) in tropical systems like hurricanes or typhoons, the lowest pressures of all are found at the center of tornadoes [source: Arizona State University]. One research team observed readings as low as 20.3 inches of mercury (688.4 hPa) at the center of a 2007 Tulia, Texas, twister [source: Blair et al.].
So what does this have to do with the window myth? Well, the thinking was that the difference between the low pressure inside a tornado and the higher pressure in the house would cause the home to explode like an overfilled balloon. So the experts advised residents to open their windows when a twister approached to help equalize the pressure. But as researchers looked more closely, they found that what lifted roofs off houses wasn't some kind of pressure bomb, but wind that got inside. So, ironically, opening the windows actually made things worse.
The moral of the story? If a tornado strikes, don't waste your time running around opening all the windows. In fact, stay away from the windows and find shelter in an interior room.
It's true that mountain tornadoes are unusual. For one, mountain air is generally cooler, making it more stable and less favorable to the formation of twisters. High elevations also leave little room between the clouds and the ground, making it difficult for tornadoes to develop and stay organized [source: Prociv].
But unusual doesn't mean impossible. Just ask Scott Newton, a backpacker trekking through the mountains of California's Sequoia National Park on July 7, 2004. Approaching Rockwell Pass, Newton noticed rotation in the clouds in front of him and began to take pictures that meteorologists later used to place the ground circulation of the tornado at an elevation of about 12,156 feet (3,705 meters) [source: Monteverdi et al.]
Lower, but much more devastating, was the Teton-Yellowstone tornado of July 21, 1987, which crossed the Continental Divide at 10,072 feet (3,070 meters). Rated EF4 (the second-strongest rating on the Fujita Scale), this beast tore a path through Yellowstone National Park and the Teton Wilderness, uprooting an estimated 1 million trees [source: Thuermer].
Clearly, tornadoes, even powerful ones, can strike mountainous areas, so it's still important to be prepared. If you can take shelter in a building, find an interior room and stay put until the threat is over. If you're backpacking, like Scott Newton, try to find some sort of depression and lie face down with your hands over your head. If possible, get away from trees in case they become airborne. Rockies or Plains — it's still a tornado!
Why not just try to outrun a tornado? After all, cars can go a lot faster! The problem with this strategy is that a lot could go wrong. What if the tornado is moving erratically? What if traffic, debris or high water blocks your escape route? The risks are just too great.
If you are already in a sturdy building, take shelter there instead of hopping in the car. In the aftermath of a 1979 tornado outbreak in Texas and Oklahoma, the U.S. Centers for Disease Control and Prevention found that half of the fatalities and injuries happened to people fleeing the storms in their cars. Tragically, many left houses that were untouched by the twisters [source: Associated Press].
But what if you're on the road and just happen to cross a tornado? If the funnel is visible and far away, try to determine its speed and direction and whether the roads are clear. If — and only if — you're sure you can make it to the nearest shelter, drive away from the storm, preferably at a right angle to its path, not directly away from it. If you can't get away, your choices will be between bad and worse. One is to get out and lie in an area lower than the roadway, protecting your head with your hands. The other is to stay in the car with your seatbelt fastened and duck below the windows while covering your head [source: Edwards].
It's true: Mobile homes aren't safe places to be during a tornado. But it's not because of some magical force that pulls storms their way. They aren't any more likely to be hit than any other structure. Still, it seems like television meteorologists always report tornado damage live from a trailer park.
The reason mobile home parks get so much attention after tornadoes is because they often suffer the heaviest damage. Much lighter than permanent homes, these structures often rest on piers with little or no anchoring. As a result, even relatively weak tornadoes can wreak havoc in these communities, destroying homes and lives that might be spared with sturdier construction. For these reasons they typically experience more than their share of tornado-related deaths, like in 2000 when 29 people were killed in mobile homes and just four in permanent homes.
So what can be done to protect people in mobile homes? As we alluded to before, trailers can be anchored to the ground, but this doesn't keep the flimsy structures from being blown apart. The only thing that really does any good is some sort of underground shelter, either a small one for a single family or a large community one for the whole park. When a tornado threatens, residents should head for these shelters or a nearby permanent building — mobile homes are not safe during tornadoes [source: Sewich].
In 2011 a powerful tornado tore through Joplin, Missouri, killing 158 people and injuring more than 1,000. Many of the casualties were people sheltering in big box stores that were effortlessly ripped open by the funnel's more than 200-mile-per-hour (321-kilometer-per-hour) winds, leaving collapsed roofs, crumbling walls and scattered inventory in their wake. While this particular tornado was exceptionally strong, it turns out that most big box stores aren't even designed to handle a storm half that potent.
Architects design big box stores to be built quickly and cheaply, and those in Joplin were no exception. Constructed of cast concrete or concrete block walls and topped with relatively lightweight roofs, these simple structures met city code, but that only guaranteed they could withstand 90-mile-per-hour (145 kilometer-per-hour) winds [source: Murphy]. Unfortunately for those hunkered down in the big box stores, their shelter didn't stand a chance.
If you do find yourself stuck in a big box store with a tornado approaching, there are some things you can do to keep yourself as safe as possible. Your best bet is to head for a safe room if the store has one. These are reinforced rooms where customers can shelter in case of severe weather. Otherwise, look for restrooms, closets or other smaller rooms that might offer protection from falling roof debris. Just remember to stay away from tall shelves — you don't want them or their contents to land on top of you [source: FEMA].
There's a good reason why spring afternoons are most closely associated with tornadoes: That's when they typically happen. What's less familiar to us is tornadoes that strike in winter and at night — and they may be even more dangerous at those times.
In the United States, the three quietest months for tornadoes are December, January and February, which makes sense because cold air is more stable than warm air. Still, this period sees an average of 114 tornadoes each year, mainly in the Southeast [source: Erdman]. Though somewhat rare, these tornadoes may actually be more dangerous because they move faster, thanks to tornado-producing winds in the upper atmosphere that accelerate in winter. This gives residents in the storm's path even less time to take cover.
Night, like winter, isn't primetime for tornado formation: Only 27 percent occur in the hours between sunset and sunrise. But 39 percent of fatalities happen at night, and tornadoes that happen between midnight and sunrise are 2.5 times as likely to cause fatalities [source: Walker et al.]. How could this be? The main reason, as you might've guessed, is because most people are sleeping at night. They're much less likely to hear warning sirens or alerts on their televisions or radios. Luckily, there's an app for that. The American Red Cross offers a program for your phone that will sound an alarm if a tornado strike is likely. A good, old-fashioned weather radio will do the same thing.
Prior to 1950 meteorologists knew so little about tornadoes that they were sometimes forbidden from using the term in forecasts. They figured it would've caused needless panic more than actually saving lives. But things have changed. Today, people often know a few days in advance that severe weather is possible, and they almost always have enough warning to take shelter when a tornado strikes. Paying attention to these warnings is a crucial part of tornado survival.
To put modern forecasting in perspective, let's take a look at how far it's come. The first documented, accurate tornado forecast happened in central Oklahoma on March 25, 1948. It was essentially based on the simple observation that weather patterns were similar to those that produced a tornado several days before. But it took a while to see improvements; warnings in the 1950s and '60s often came just seconds before a twister hit [source: Galvin]. By the 1980s, however, radar technology allowed meteorologists to see conditions inside the storms, increasing warning time to five minutes. Additional radar advances in 1993 nearly doubled that lead time, and today warnings can give people 15 minutes or more to prepare [source: Howard]. That may not sound like very long, but it certainly gives you a lot more options than a few seconds would.
Of course, forecasting still isn't perfect, and sometimes meteorologists can be wrong. But choosing to ignore warnings just because they aren't always right is asking for trouble. When it comes to tornado forecasts, don't take them for granted — take shelter.
Last editorial update on Apr 25, 2019 01:16:21 pm.
NOAA is expecting widespread flooding throughout the United States this spring. HowStuffWorks tells you how to get your home and self ready.
Author's Note: 10 Myths About Surviving a Tornado
Tornadoes are serious business: I know firsthand from my 21 years living in the Southeast. Almost every spring and summer I'd spend a few afternoons or evenings huddled in a hallway or closet while the weather radio blasted the latest warnings. That voice — somewhere between computer and human — became synonymous with the fearful uncertainty that filled the space between the initial alert and the "all clear." Now I've moved to the Rocky Mountain region, and while I know from writing this article that I'm not completely in the clear, I haven't been spending nearly as much time in a hall or closet. That's something I'm certainly glad to have left behind.
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