While researchers have long focused on El Nio -- warm ocean temperatures leading to odd spells of rain and dry weather -- climate experts are not sure what caused the winter deluges that struck northern California, Oregon and Washington in the us in the past two years. Was it the handiwork of El Nio's contrary, 'wicked sister' La Nia? Also called a cold event, La Nia begins with cooler-than-normal sea-surface temperatures in the tropical eastern Pacific and warmer water in the western Pacific. The temperature difference is only a few degrees Fahrenheit, but it is enough to redirect the tropical jet stream, laden with winter snowstorms to the us. While all 'crazy weather' cannot be attributed to this phenomenon, strong La Nias were observed in 1995 and 1996. Scientists will be keeping a close watch on La Nia to help improve long-range weather forecasting models ( Popular Science , Vol 251, No 3).
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