La Nina spawns extreme weather

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By Patrick Mar
CNN student bureau
Seattle, Wa.

Characterized by unusually cold ocean temperatures in the Equatorial Pacific, La Niņa, Spanish for "little girl," could mean more spring flooding. The weather system also could bring drought to much of the U.S. Midwest and Great Plains regions.

Most of the country will experience hotter than normal temperatures this summer because of "La Nina," which will remain in force through August, according to the National Oceanic and Atmospheric Administration.

NOAA's prediction also includes heavy monsoon-like rains in Arizona, New Mexico, southern Colorado and Utah, throughout July and August.

La Niņa is compared to El Niņo, which is characterized by unusually warm ocean temperatures in the Equatorial Pacific.

"If we get things where we suddenly get 80 degree temperatures in May and rain, all the snow in the cascades start to melt, we may again get record flooding."

How will La Nina bring about the cold? One possibility is that the jet streams that normally hit the west coast straight on will instead swing up into Alaska and dive down the coast, bringing along cold arctic winds with it. That will likely cause a dramatic change in temperature.

Weather experts are not sure exactly what causes La Nina, but there are many theories.

"Essentially, [the theories] involve ocean-atmosphere interactions in the tropical Pacific region, and the slow evolution of the upper ocean thermal structure," reports the west coast headquarters of the NOAA.

NOAA uses a system of buoys mounted with measuring devices. These buoys are placed at intervals along specific lines of longitude throughout the Pacific and Atlantic Oceans. Every year, NOAA's research ships visit the buoys and collect the recorded data.

The buoys also contain weather-sensing devices that test for surface temperatures, subsurface temperatures, wind speed, and other indications of changing weather. Even with the aid of these devices, NOAA still has not been able to calculate the exact behavior of La Nina.

La Nina started in mid 1998. NOAA forecasters say La Nina may finally end in August when readings from a network of mid-ocean weather stations suggest Pacific Ocean temperatures could return to normal.

"All of the computer weather models agree that most of the U.S. will be warmer than usual, but at least we can see the end coming for La Nina," said Ants Leetmaa, director of NOAA's Climate Prediction Center.