© Don Kausler/The Birmingham News/Associated PressA funnel cloud approaches Tuscaloosa, Ala., where widespread damage and multiple deaths occurred from the storm on April 27.
And no matter where twisters touch down - from Mapleton, Ia., to Joplin, Mo. - they leave a strange new reality in their wake. But reality has little to do with some of the ideas that have swirled up around them over the years. Here's a look at the most common myths and the truth behind them.
MYTH: Global warming is the reason there have been so many tornadoes in recent years.
REALITY: Probably not. The number of severe tornadoes has actually declined in the United States, even as temperatures have risen.
Even so, climate scientists have predicted for years that global warming will cause more weather extremes, and statistics suggest that this has started to occur. In general, more precipitation is falling, often leading to flash floods, and heat waves are becoming more common, the New York Times reported earlier this week.
But so far, at least, scientists are reluctant to pin any specific weather events on human-driven global warming. Research won't be able to explain this year's strange weather for at least a year or two, and it may be decades before scientists can demonstrate whether or not human-triggered climate change is affecting tornado frequency.
Comment: A number of scientists are rejecting the theory of global warming - and in fact some say we are on the verge of a mini-ice age. For more information read Eminent geophysicist rejects global warming theory, says world on verge of 'mini ice age' and Global Warming And The Corruption Of Science.
MYTH: The sky always turns green before a tornado.
REALITY: Sometimes, but not always. A severe thunderstorm contains lots of water, either in the form of rain or hail, and water tends to scatter reddish light. When a storm strikes suddenly, in an otherwise clear sky, sunlight traveling through the atmosphere loses its blue wavelengths first and then the red wavelengths as it passes through the storm. That leaves only the middle part of the spectrum, which is green or greenish.
MYTH: Tornadoes strike only in so-called Tornado Alley.
REALITY: It's true that most tornadoes rip through the wide open plains from Texas to Minnesota, but they can hit elsewhere, too. Hurricanes have been known to spawn tornadoes in Florida, and a waterspout - essentially a tornado on water - touched down near Honolulu's Pearl Harbor earlier this month.
MYTH: Tornadoes never cross a river or strike where two rivers meet.
REALITY: A tornado can hit anywhere and at any time," WHO-TV meteorologist Jeriann Ritter said, adding that a twister touched down last Saturday in La Crosse, Wis. The EF2 touched down first near the city's Green Island Park, smack in the middle of the Mississippi River.
MYTH: Tornadoes don't strike cities.
REALITY: See above - "A tornado can hit anywhere and at any time." See also - Joplin, Mo. The EF5 tornado that killed more than 120 people earlier this week didn't slow down even in the most developed parts of the metro area, which was home to nearly 175,000. It was one of the deadliest single tornadoes in recorded history.
Although some research indicates that the heat that hovers over major urban areas with tall buildings can diffuse small tornadoes, there are enough exceptions to the rule to prove it wrong. In the past 40 years, tornadoes have struck St. Louis and its suburbs 22 times (although none have struck its downtown core).
The origin of this myth can be traced to simple geography: There are only a handful of major cities in Tornado Alley.
MYTH: If you're on the road when a tornado hits, the safest place to hide is under a highway overpass.
REALITY: "Not true," Ritter said. "Overpasses are a deadly place to be in a tornado. You'll be much safer in a low, flat location, like a ditch." An overpass can actually become a "wind funnel" and trap debris, added Jeff Johnson, a warning coordination meteorologist with 17 years of experience with the National Weather Service in Johnston. He suspects the overpass myth began with a video that circulated in the 1990s, when a team of stormwatchers sought refuge under a highway bridge and shot footage of a twister that just barely missed them.
The added danger: Clusters of parked cars under bridges create additional hazards for other motorists.
MYTH: If you're at home, open the windows before a tornado hits to equalize the air pressure.
REALITY: Don't waste the time. Although the air pressure at the very center of a tornado can be low enough to cause explosive effects, the bigger danger is from flying debris and the wind itself.
It's likely this myth stems from wishful thinking and the instinct to do something - anything - to prepare for the storm.
MYTH: The safest place to hide inside is the southwest corner of the basement.
REALITY: The basement is usually safe, but the particular corner doesn't matter.
Tornadoes can switch directions quickly, but it's true that most tornadoes in the Midwest carve a path from the southwest to the northeast. That may have prompted the myth's originators to believe that buildings would shift or collapse in the same direction. One of the earliest books on the subject, John Park Finley's 1887 Tornadoes, warned that people should "under no circumstances, whether in a building or in a cellar, ever take a position in a northeast room, in a northeast corner, or an east room, or against an east wall."
But later research has debunked that advice. It's more important to simply hunker down below ground or, if that's not possible, in the building's smallest room with the fewest number of exterior walls.
MYTH: Tornadoes skip up and down off the ground.
REALITY: Although a tornado can gain strength and weaken over the course of its run, it doesn't actually skip over the surface of the ground. A storm's often random pattern of destruction, where certain houses are leveled while the ones next door are intact, has more to do with the quality of construction or the particular orientation of the building's walls to the brunt of the wind. Johnson, of the National Weather Service, said that hurricane straps or clips - internal reinforcements that connect the ceiling rafters to the wall studs - increase the chances that a building will end up in one piece.
MYTH: Tornadoes are more likely to strike mobile home parks than other areas.
REALITY: Not true, but the statistics are grim: People who live in mobile homes or trailers are 15 times more likely to die in a tornado than those who live in permanent housing, according to the Times.
Still, the overall risk of dying in a twister is just 1 in 5 million. The death rate is nine times less than it was before 1925, when tornadoes killed 695 in Missouri, Illinois and Indiana. The tragedy prompted more public awareness, better alerting systems and stronger building designs.
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