A moderate El Nino building across the tropical Pacific will last through at least the winter, likely affecting weather across the U.S.

Experts at the government`s Climate Prediction Center, in their monthly El Nino status report, are continuing to see moderate El Nino conditions throughout the tropical Pacific off the South American coast. Certain observations seen in the tropical Pacific indicate that the moderate El Nino will continue to strengthen as the calendar flips from 2009 to 2010.

El Nino, the abnormal warming of the Pacific Ocean off South America`s west coast, alters climate patterns around the world and causes shifts in North America`s jet stream, the high altitude winds that steer storms. El Nino`s intensity guides the severity of these shifting weather patterns.

A moderate to strong El Nino usually produces warmer than normal temperatures with significantly less snowfall in the northern Plains, upper Midwest and western Great Lakes. Strong El Ninos keep the brutal arctic air bottled up in Canada.

An active southern jet stream would bring more rain and mountain snow to the southern U.S. from California to the Gulf Coast, accompanied by cooler temperatures. This increase in precipitation can lead to dangerous flooding and mudslides in California and the Southwest. This is particularly dangerous in wildfire ravage areas of southern California and the Southwest, where heavy rain can cause devastating mudslides.

The Southeast would more than likely see frequent winter storms and colder than normal temperatures during a strong El Nino, while the displaced jet stream will steer storms away from the Ohio Valley, producing less rain and snow there.

El Nino could also be a leading factor in the relatively quiet 2009 Atlantic Hurricane Season compared to the hyperactive years seen over the last half decade. Past hurricane seasons with a weak to moderate El Nino have seen lower hurricane activity as increased wind shear in the Gulf of Mexico and Caribbean Sea slows tropical system development. Wind shear has been a common problem affecting tropical development this year.

WeatherBug will continue to be a reliable source to get up-to-date information on El Nino and how it can impact weather in your neighborhood.

Contributing: Stephen Baxter

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