Science Scope

Looking beyond 'green skies' to predict tornadoes

Looking beyond 'green skies' to predict tornadoes

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Scientists are looking at whether tornado prediction technology can improve and whether climate change is making twisters more frequent.

In this season of deadly tornadoes, as the aftereffects of the deadliest of them all – Sunday’s twister in Joplin, Mo. – are still being ascertained, many are asking whether tornado prediction technology can improve.

According to folk wisdom “green skies” signal that a tornado is basically upon you, and unfortunately, nowadays, tornado prediction technology can only see a bit further ahead. In Joplin on Sunday, some residents only had 20 minutes’ warning – despite the improvements in tornado forecasting in recent years.

Compared to hurricanes, tornadoes are extremely difficult to foresee. While the conditions that give rise to hurricanes span the globe and build much more slowly, tornadoes are more susceptible to “the butterfly effect” – the theory that small perturbations, such as the flapping of a butterfly’s wings, can lead to large consequences.

The biggest advance in tornado prediction has come from “the ensemble forecast” which relies on computer models that can project atmospheric conditions as far out as five days in advance. By running 20 at a time, forecasters can see when many of the models begin to agree versus when their projections cover a range of scenarios.

Even then, meteorologists can only address a broad area. They can’t pinpoint the place a tornado will touch down with much accuracy until a storm occurs. The ingredients necessary for a tornado are moist air, winds that change speed or direction with height, and cold air that descends and forces the warm air up. As the warm air ascends and the cold air descends, the two rapidly begin to spin into a tornado. Because these circumstances can escalate into a twister so quickly, meteorologists cannot even give hours of notice.

Some scientist are looking to improve tornado prediction technology through other methods, such as investigating soil moisture levels.

As scientists work to improve tornado prediction technology, climatologists are also wondering whether climate change could foster more tornadoes. Data from the last 60 years show that the number of tornadoes has increased significantly, but most scientists believe this is due to better tracking, and does not prove whether or not they are becoming more common.

However, one theory is that climate change could cause more tornadoes in the U.S. by more frequently producing the circumstances that produce tornadoes, such as a warmer Gulf of Mexico that sends humid air – a central ingredient in tornadoes – northward into states such as Alabama, where twisters killed hundreds last month.

Researchers are also investigating whether La Nina – the climate pattern in which the sea surface temperature of the equatorial Pacific Ocean is lower than average – affects the likelihood of twisters by shifting the jet stream, the air current that flows across the U.S. from west to east.

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Laura Shin

Features Editor

Laura Shin has been published in The New York Times, The Wall Street Journal and The Los Angeles Times, and is currently a contributor at Forbes. Previously, she worked at Newsweek, the New York Times, Wall Street Journal and LearnVest. She holds degrees from Stanford University and Columbia University's Graduate School of Journalism. Follow her on Twitter. Disclosure