The Science Of Predicting Tornadoes

On the heels of Sunday night's devastating Midwest tornadoes, NPR's Jon Hamilton talks to Mary Louise Kelly about why tornadoes are still so hard to predict.

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MARY LOUISE KELLY, Host:

The destruction in Joplin marks the second major outbreak of tornadoes this year. In April there were hundreds of twisters, making it one of the busiest months on record. Well, joining us now to talk about the science of tornadoes is NPR's Jon Hamilton. Hey, Jon.

JON HAMILTON: Hi.

LOUISE KELLY: So we just heard Missy Shelton there describing thunderstorms over Joplin today. Do we know any more - are there more tornadoes in the immediate future for that area?

HAMILTON: Well, at the moment the U.S. Storm Prediction Center - that's the place that keeps track of this stuff - they're keeping an eye on two places they say are showing moderate risk of severe storms, the kind of storms that could lead to tornadoes. And one of those areas is near Joplin, Missouri. But right now they have issued no tornado warnings. Obviously that could change during the day. The ground gets warmer. Conditions (unintelligible) but at the moment it doesn't look like there probably will be a repeat of yesterday.

LOUISE KELLY: Okay. And as they look ahead to the short to medium term forecast, weeks and months down the road, is there any way to know whether this year is going to continue to be particularly bad?

HAMILTON: You know, that's something I have been asking meteorologists for the past couple of weeks, and they've been telling me they really just don't know. What they say is that, you know, tornadoes are not like hurricanes, where you can do a seasonal forecast every year. You know, you can do that because hurricanes are these large-scale events that are affected by things that take months to change. So for instance, you know, whether it's El Nino or La Nina conditions, clearly it affects hurricanes.

But the effect of those things on tornadoes really just isn't clear. The conditions that lead to a tornado, they're related to thunder storms in a particular area and where masses of warm and cold air are meeting, you know, whether there's convention - that's warm air rising. And those are things that can change dramatically over just a couple of days.

Also, remember that, you know, like a hurricane is huge. It can be like 100 miles across and it may exist for a week or more, whereas a big tornado like the one that hit Joplin might be only a mile across and its life can be measured in minutes.

LOUISE KELLY: So much harder to pinpoint where exactly the path might end up taking it. Well, I mean obviously one of the big things that affects people being able to get out of the path of these things is how much warning they have. A few minutes can make a big difference. How good are scientists at being able to forecast a tornado that's headed towards somebody?

HAMILTON: Well, the few minutes applies to when a tornado's actually formed and then if there's a siren it may go off, the radio starts broadcasting. But what's changed in recent years, that meteorologists at the Storm Prediction Center have actually gotten quite good at making short term predictions about whether these are conditions where it's likely to form. Short term on the order of a day or two.

So you know, one thing they look at is something called supercells. A supercell is a type of thunderstorm that has this rotating updraft and it often can lead to a tornado. So for instance, if you look back in late April, you know, they were telling people in the South, in Alabama and elsewhere, they were saying, you know, this looks like we're going to have a major outbreak, or there's a potential there. And they nailed it. They were exactly right.

There were hundreds of tornadoes, and of course hundreds of people who were killed. You know, the problem is, of course, even once a tornado has formed, you really don't know if it's going to hit your house or even your neighborhood.

LOUISE KELLY: And Jon, climate change - does that have anything to do with what we're seeing this spring?

HAMILTON: Well, you know, when people talk about extreme weather, climate change always comes up. And the scientists say it's really hard to say. You know, people point out that there - people who think there's a connection point out that there are more tornadoes reported than there used to be. Scientists say, yeah, but if you only look at the big tornadoes, the ones you probably(ph) wouldn't miss, no, it hasn't - hasn't changed.

So if you go and you read the latest report from the Intergovernmental Panel on Climate Change, they say it's just not clear.

LOUISE KELLY: Just not clear. Alright, thanks so much.

HAMILTON: You're welcome.

LOUISE KELLY: That's NPR's science correspondent Jon Hamilton.

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