龙卷风可以预测吗?

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目前龙卷风在预报上还是比较困难的。但随着科学技术的不断发展，特别是多普勒天气雷达的不断完善，我们对龙卷的认识及预报都有所提高。目前预报方法主要是根据天气条件判断在某一地区产生龙卷的可能性，然后通过多普勒天气雷达监测，及时发出警报。龙卷还是可以预测的。

Yael: What are you doing with that shovel, Don?
Don: I'm digging a hole for a tornado shelter to get ready for next winter, Yaël.

Y: A tornado shelter for winter?

D: Yep. We're going to have lots of tornadoes in the midwest this year.

Y: How could you know that?

D: Because the sea surface temperature in the eastern tropical Pacific Ocean is cooler.

Y: Now you are sounding crazy, Don.

D: Not as crazy as you might think. Tropical Pacific water temperatures fluctuate in two-to seven-year cycles, and those temperature events can last five months or longer. For years we've known that during El Niño events, when the Pacific waters are warmer, the weather is generally wetter in North and South America and Africa, and can cause massive floods. At the same time, it's drier in Asia and Australia, causing droughts. During La Nina events, when the Pacific is cooler, it's just the opposite.

Y: So, what does this have to do with winter tornadoes?

D: Since tornadoes are so destructive, meteorologists at the NOAA Storm Prediction Center are always looking for new ways to predict where and when they will occur. They have discovered that during El Nino years, more winter tornadoes occur in Florida and the Gulf states. During La Niña years, there are more tornadoes in Texas and the upper Midwest.

Y: So, knowing what's happening in the Pacific gives meteorologists advance warning.

D: Exactly right. Isn't it amazing?

Y: Almost as amazing as your building a tornado shelter when you already have a basement for protection.

D: Hm. I guess I hadn't thought of that.