VOA慢速英语:龙卷风预测能力增强 但伤亡仍旧发生

Sometimes when predicting the powerful wind storms called tornadoes, an expert can get everything technically right, and yet very bad things happen anyway.

On March 3, a deadly tornado passed through southern Alabama. For several days before, United States government severe storm experts warned that conditions at the time were right for causing tornadoes. Later, they issued a warning that a severe tornado could take place within an hour.

It did. And, 23 people were killed.

Russ Schumacher is a professor at Colorado State University. He studies and teaches the science of weather. Schumacher told the Associated Press the weather predictions announced for Alabama were as exact as possible.

But with so many people killed, "was it a success or a failure or both?" he asked.

Experts "painted a pretty clear picture that something bad was going to happen," said Schumacher. And "there's ... success in that." But, he added "we don't like to see entire communities to be turned upside-down like this. So there's more to be done."

Predicting correctly where a tornado is going to go is still beyond the limits of modern meteorology. That is why warnings went out in Alabama for a large two county area when a tornado might be only half a mile wide. And getting people to listen and use the necessary safety measures is another issue completely.

Predicting tornadoes combines the hard physics of meteorology and the softer human qualities of social science. It also includes more than a little uNPRedictability.

The National Oceanic and Atmospheric Administration, or NOAA, is the main U.S. government agency dealing with weather research. At NOAA's Storm Prediction Center in Norman, Oklahoma, scientists look for the conditions that can create a tornado. These include warm air coming from the south that contains lots of water, and stormy weather from the west, which can bring instability.

That is when you can get severe weather systems called supercells, which is where tornadoes come from.

But maybe only 10 to 20 percent of supercells produce tornadoes, said Bill Bunting. He is the operations chief for the storm prediction center. There are other things at work, including uNPRedictable wind behavior known as wind shear. There is also the amount of cold air present, the size of the rain drops and even other unknown qualities at play.

Bunting noted that given all that, the best meteorologists can do is say when the conditions are seven to eight days away from being the best for tornadoes. However, four to five days is more usual.

Even that does not mean they will happen, especially not over all of the large area meteorologists give in their several-day-out warnings.

From 1994 to 2017, the U.S. weather service's false warning rate for tornado warnings was 74 percent. Yet weather service spokeswoman Maureen O'Leary noted that last year it dropped to 69 percent.

The problem is that a tornado is a rare, small event that ends quickly. It is harder to predict than huge weather events like hurricanes or big winter storms. A one-mile change in a tornado's path can mean the difference between destroying a field and doing damage in a populated area, said Bill Bunting.

Bunting's office might warn people to watch out across a five- or six-county area or even a two- or three-state region. But "only a very, very small area of that risk area will actually experience dangerous conditions," he said.

University of Oklahoma meteorology professor Howard Bluestein added that people who do not get hit may not listen to warnings the next time.

That is the social problem, which may be even bigger than the meteorology one, Bluestein said. And that is where Kim Klockow-McClain gets involved. She is a researcher for NOAA's National Severe Storms Laboratory, also in Oklahoma. Klockow-McMclain specializes in trying to find out why some people listen and react to warnings and others do not.

"Social sciences, I think, are really going to the heart of the issue," she said. "You've got to receive the message. You've got to understand it and know what to be able to do about it."

For example, mobile homes are especially vulnerable to tornadoes. But the people who live in them are less likely to seek or receive storm warnings, Klockow-McClain said. Even though they are told to get out, studies show people in mobile homes still "shelter in place," she said. "They think it's the best thing they can do or the only thing they can do."

It is not.

The weather service started to change from just centering their efforts on better predictions to better communication of warnings in 2011. That is because the agency noticed the predictions had improved but the results were still similar to what they were in the 1950s, '60s and '70s, Klockow-McClain said.

I'm Pete Musto.

Seth Borenstein reported this story for the Associated Press. Pete Musto adapted it for VOA Learning English. Caty Weaver was the editor. We want to hear from you. Write to us in the Comments Section or on www.hxen.net .