Source: NASA

The La Niña weather pattern in the Pacific Ocean may influence rainfall amounts in 2011 and add one more worrisome factor, drought, for the upcoming growing season.

The La Niña pattern is characterized by unusually cold ocean temperatures in the eastern equatorial Pacific, as compared to El Niño, which is characterized by unusually warm ocean temperatures. A strong La Niña is currently dominating the Pacific Ocean.

"La Niña occurs only when both the ocean and the atmosphere change together, and in 2010, they have," says oceanographer David Adamec of the Goddard Space Flight Center. "The unusual ocean temperatures and imbalance in air pressures alter weather patterns across the world."

The weather pattern is already having an impact around the world including heavy rains and flooding in Australia and Asia. "It also has resulted in flooding in northern South America and drought conditions in Argentina," said Bill Patzert, an oceanographer and climatologist at NASA's Jet Propulsion Laboratory. "(La Niña) is spreading her curses and blessings across the planet. She's the real deal."

La Niña typically affects weather patterns in North America beginning in January. "For 'normal' effects in the United States, look for cold in the Upper Plains, dry and warm weather in California, dry weather in the southeast, especially Florida, and unusually soggy weather in the Northwest," says Adamec.

The La Niña tends to produce more weather extremes and may contribute to drought. "This is the strongest La Niña in the past 60 years," says Elwynn Taylor, professor of ag meteorology at Iowa State University. "The forecasts are that the La Niña will continue into April. If indeed the La Niña fades away in April, in could be ideal, leaving the soil a little dry on top, then go on to a normal year."

If La Niña stays active through the summer, it could have drastic consequences. "If La Niña continues into June, we could have a disaster on our hands," Taylor says. Another possible scenario would be a drought, which, when averages are taken into consideration, is overdue,

"1988 was our last major drought," says Taylor. Historically, the average time between severe droughts in the Corn Belt is 19 years. "We know this by studying tree rings, which have been recorded for 800 years."

Based on this study of tree rings, Taylor says that the longest time period observed between droughts is 23 years. "If we make it through 2011 without drought, we will break an 800-year-old record."

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