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Call them twisters or tornadoes. They are nature's most violent storms with swirling winds that can top 300 miles per hour. About 800 twisters sweep through the US every year, more than anywhere else in the world. The hardest-hit area is a swath of the Great Plains from Texas to South Dakota, known as Tornado Alley. Here, warm air flows up from the Gulf of Mexico in the spring and summer and crashes into cold air pushing down from Canada. The meeting produces violent thunderstorms called supercells.
龍卷風是大自然最為猛烈的風暴，他們自帶旋轉的狂風，時速最高可達300英里。每年，美國都會遭受近800場龍卷風，沒有哪個地方的遭受次數比美國更高。得克薩斯州到南達科塔之間，受創最為慘重的是北美大平原了，這里是龍卷道。這里春天和夏天的時候，暖空氣會從墨西哥灣上升，然后與來自加拿大的冷空氣相撞。交匯處會產生強烈的雷暴，也稱超級單體。
Scientists don't completely understand how or when tornados form, but they do know a supercell like this one can produce a twister if the conditions are right. As more moist air flows into a storm, it gets pushed up and twisted by upper level winds. As this rotating column of air gathers force, conditions are right for a collision below. When rain cooled downdrafts hit warm air near the ground, a low hanging revolving cloud forms beneath the cell. A tornado is imminent.
科學家不是十分清楚龍卷風形成的方式和時間點，但他們可以肯定的是：一旦條件合適，類似這樣的超級單體就可以產生龍卷風。濕空氣進入風暴里之后，就會受到推力作用，被上層的風帶動著旋轉。這種旋轉氣柱的力量越來越大，等條件合適的時候，就會發生下面的碰撞。經過雨水冷卻的下降氣流與地表附近的暖空氣碰撞，單體下面的低空就會產生旋轉的云。這時候就快產生龍卷風了。
Tornadoes don't last long, anywhere from 20 seconds to an hour. But it can take years to recover from the devastation. These storms kill nearly 90 people each year in the US and cause millions of dollars worth of damage. When a tornado is spotted, experts advise going to a basement, staying away from any windows or climbing into a first floor bathtub. While most people run for safety when a twister appears, some scientists actually race to need it. These storm chasers hunt down tornadoes, trying to get right in the twister's path.
龍卷風持續時間很短，從20秒到1小時不等。但其造成的損害卻是數年才能修復的。每年，龍卷風都會導致近90人死亡，其造成的損失達數百萬美元。一旦看到龍卷風，專家建議去地下室待著，避開窗戶，也不要在一層的浴缸里待著。大多數人對龍卷風避猶不及，一心想著保平安，但有些科學家卻對龍卷風趨之若鶩。他們苦苦追尋龍卷風，試圖與龍卷風打個照面兒。
They encounter incredible cloud movement, torrential rain, severe winds and hail, lightening, breathtaking storm structures. When they finally locate a twister, they measure it using special tools. These scientists hope to someday predict exactly when and where tornadoes will strike. Little can prevent the damage caused by tornadoes, but better forecasting could save more lives, giving survivors the chance to rebuild after living through one of the most violent storms on earth.
他們會遇到難以想象的云體移動、傾盆大雨、強風、冰雹、閃電以及令人嘆為觀止的風暴。一旦他們發現了龍卷風，就會用特殊工具來進行測量。這些科學家希望有一天可以準確預測龍卷風發生的時間和地點。很難避免龍卷風造成損失，但預測能力的提高可以挽救更多的生命，讓幸存者有機會重建家園，就算他們曾經遭遇了世界上最可怕的風暴之一。
