Stormy Weather Predictor

With a few exceptions, the winter of 1998-99 wasn't much of a winter at all along the East Coast. CBS News Correspondent John Roberts reports that according to climatologists, what's behind the mild season is something called the North Atlantic Oscillation - the NAO.

"In the same way that El Nino is the primary generator of weather in the tropical Atlantic, the NAO is the primary governor of storms in the wintertime season in the North Atlantic region," says Heidi Cullen of the Lamont-Doherty Earth Observatory.

The NAO is driven by a low-pressure system that sits over Iceland and a high near the Azores. When the NAO is strong, it creates winds across the Northeast that act as a barrier to arctic air. Coastal waters warm, resulting in mild, wet winters. For most of the past 30 years, the NAO has been in a strong phase.

"At the same time, we have witnessed much warmer winters in the East Coast US and much less snow," says Yochanan Kushnir, also of Lamont-Doherty.

But once in a while, the NAO weakens. The last time that happened was the famous winter of 1996. Arctic air penetrated deep into the Atlantic seaboard. 21 storms brought record amounts of snow to the Northeast.

Now, a group of researchers in England believes winters like that might be predictable. They've found Atlantic sea surface temperatures in the fall are an indication of what the NAO will do.

"If you want to make a prediction that the next five winters might be wetter than average or warmer than on average, then that might be possible in the future," says Mark Rodwell of the Center for Climate Prediction and Research.

And there's also new evidence that the NAO's effects linger - all the way into summer. In years when the oscillation is strong, as it is this year, there are fewer hurricanes. In a weak year, like 1996, there are more.

Hugh Willoughby of the NOAA-Hurricane Research Division claims,"It's almost a doubling of the real intense hurricanes that do the most damage."

All of this has yet to be fully understood. But climatologists will go so far as to say that what the NAO gives us in winter is a pretty good indication of how the next few months will go. And that means the Atlantic coast of the United States may have a warmer, wetter spring, and a long, hot summer.

  • CBSNews.com staff CBSNews.com staff

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