Magazine article Science News

Combined Forces Create Southwest Draught

Magazine article Science News

Combined Forces Create Southwest Draught

Article excerpt

Hot, crop-killing weather ruled the Southwest and Great Plains of the United States during the first half of 1996, with record books in Texas and Oklahoma proving it the driest winter and spring since record keeping began in 1895. In a move to explain the precipitation deficit, meteorologists at the National Weather Service's Climate Prediction Center in Camp Springs, Md., released a report on the drought last month. Although Arizona, Nebraska, New Mexico, Oklahoma, and Texas bore the brunt of the dry spell, researchers said it was part of an unusual weather pattern that affected the whole Northern Hemisphere during late 1995 and early 1996.

The first puzzle piece that they found was a wide area of relatively cool water last year across the central Pacific Ocean. Dubbed La Nina by climate scientists, the lower-than-normal water temperatures are the flip side of the better-known El Nino, which elevates water temperatures in the same region. Both deviations can influence weather on a global scale.

La Nina alters thunderstorm activity over the central Pacific, sending the seasonal storm track and jet stream to the north and stationing a high-pressure dome over the Southwest, according to Gerald Bell, a coauthor of the report. This northbound jet stream triggered above-normal rainfall and flooding in the Pacific Northwest.

The report finds another missing piece in a unique wind circulation pattern over the North Atlantic that increased the drought's scope. …

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