美国国家公共电台 NPR Scientists Know How Tornadoes Form, But They Are Hard To Predict（在线收听）

ARI SHAPIRO, HOST:

Last night, tornadoes again touched down across the central U.S. In Prestonsburg, Ky., a roof torn from a building killed a person driving through downtown. We've been hearing stories like this all month - tornadoes leaving a trail of destruction from Texas, all the way up to Maryland. Scientists know how tornadoes form, but they're nearly impossible to predict. Patrick Marsh is a meteorologist at the National Oceanic and Atmospheric Administration's Storm Prediction Center. And I asked him why it's so hard to forecast where tornadoes will touch down.

PATRICK MARSH: So if you stop and think about it, before you can have a tornado, you have to have a thunderstorm, and to have a thunderstorm, there are four basic ingredients that you need to be able to assess and predict, and that's moisture, instability, lift and wind shear. And so we have to track all four of those fields through the atmosphere and find where they're going to come together before we can even predict where the thunderstorms are going to occur. And then once we have a thunderstorm, we have to identify the subset of thunderstorms that could go on to produce tornadoes.

SHAPIRO: How unusual is it to have this many tornadoes in such a short period of time?

MARSH: It's actually quite unusual. We've had long stretches where we've had tornadoes over a long period of time, but the difference was we would have a day or two here or there where we kind of had a reprieve. We're not seeing the reprieve this time, and that's what makes this outbreak so unique.

SHAPIRO: I know that climate change plays a role in exacerbating a lot of natural disasters, but it's a little murkier with tornadoes. Can you explain why that is?

MARSH: Even though the vast majority of the world's tornadoes occur in the United States, it's still somewhere on the order of about 1,200 tornadoes a year. And so when you think about how much real estate, how much land there is in the United States, that's not a lot of tornadoes for us to observe and predict. And so our dataset for tornadoes is actually quite limited. And for us to be able to do attribution studies to assess whether or not changes we see are related to climate change or other factors, we need a much bigger tornado dataset, or we need better statistics to assess this.

Hopefully, in the next few years, we'll be able to say something more definitive, but at this time, we just don't have the tools to do so.

SHAPIRO: Is it your hope that in our lifetimes we'll be able to predict tornadoes as definitively as we can anticipate other weather events that may be less catastrophic?

MARSH: I would love to be able to tell somebody, you know, tomorrow there's going to be a tornado that's going to go through downtown Oklahoma City. But the atmosphere is inherently chaotic, and I don't know if we'll ever be able to get there. But we are working on ways to kind of mitigate the fact that we won't be able to be as deterministic as people want. Some of the tools that we're developing is a process called Warn-On Forecast, an idea that we can run high-resolution numerical simulations out several hours in advance and be able to tell people there's a 20% chance of a tornado moving within a few miles of downtown Oklahoma City in the next two hours.

And hopefully, this allows things like hospitals to take safety precautions that they might not be able to implement if they only have a few minutes, which is what the current paradigm is. For example, you could cut down on elective surgery, so you don't run the risk of somebody being in surgery as a tornado hits. You can move patients out of their rooms into their hallways at a much slower pace, rather than the frenetic pace of a tornado bearing down on you. And that will also crack down on the amount of injuries and the risk for additional injuries.

SHAPIRO: Given that there will apparently always be uncertainty and some false alarms surrounding tornado forecasting, what's your best advice to people who might be living in zones that are prone to them?

MARSH: The best advice I can offer somebody is do not wait until severe weather is threatening you to figure out what you're going to do. Take a few minutes right now, as you listen to this interview, to talk to your spouse, your significant other, your family about what you would do if tornadoes or other severe thunderstorms were to threaten you. In a nutshell, what you can do for tornadoes is you want to get into a well-built structure, you want to get to the lowest floor - and this does not necessarily mean below ground - and you want to put as many walls between you and the outside.

So in a nutshell, what I try to tell people is get in, get down and cover up.

SHAPIRO: Patrick Marsh, thanks so much for joining us today.

MARSH: Thank you very much for having me.

SHAPIRO: He's a meteorologist at the National Oceanic and Atmospheric Administration's Storm Prediction Center.

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