La Nina and El Nino

Sea surface temperatures play a major role in global weather and nowhere is that more evident then in El Nino and La Nina patterns. These type of patterns often lead to weather extremes, some of which can be seen in our own backyards. Sea surface temperatures indicate that we'll have a La Nina this winter, which could mean a season of weather extremes across parts of the United States.

What is La Nina and El Nino?

La Nina is described as cooler-than-normal sea surface temperatures in the central and eastern Pacific Ocean, near the equator off the west coast of South America. El Nino is like La Nina's brother, the totally opposite and attention grabbing brother. This is described as warmer-than-normal sea surface temperatures in the same area of the Pacific Ocean.

What Causes La Nina and El Nino?

Simply put, easterly trade winds over the equatorial Pacific Ocean are partly to blame for both phenomenon. For La Nina, the easterly trade winds strengthen. This blows more warm water west, and allows cold water below the ocean's surface to push towards the top near the South American coast to replace the warm water.

In an El Nino, the opposite occurs. The easterly trade winds become weaker, and can even reverse direction. The warm Pacific Ocean becomes nearly stationary or pushes eastward and gains heat. Besides affecting weather, El Nino has also been known to hurt fishing off the coast of Peru.

What Does All of This Mean for the Weather?

We're already seeing affects of the building La Nina. A typical La Nina winter will feature drier and milder conditions across the South, much like what we're seeing in the current Southeast drought and elevated fire conditions. The Pacific Northwest will become wetter than normal, while the Northeast will have cold periods, but these are usually short lived. You can read AccuWeather's 2010-2011 Winter Forecast by Chief Long Range Meteorologist Joe Bastardihere.

In an El Nino winter, we see what we had last season. The southern branch of the jet stream gets displaced across the Deep south, leading to wetter conditions from Los Angeles to the Southeast. The Northeast typically has stormy winters, which in the case of last season led to "Snowmageddon." Finally the Northwest is typically milder.

In other parts of world, La Nina and El Nino can affect Asia's Monsoon's and rainfall from Australia to Peru.

How Long Will This All Last?

Typically a La Nina lasts 9 to 12 months, while an El Nino will last roughly a year. As for this year's La Nina, forecast models are indicating slight strengthening through October and then a steady period in November and December. All of the models have the La Nina weakening throughout the spring and early summer.