In case anyone is interested or even just idly curious, we've been in a La Nina weather pattern that started in the third quarter of 2007, weakened during 2008 and has come back this winter with a vengeance, which accounts for the weather extremes the US (and other countries) has been experiencing.
A La Niña event occurs when cooler than normal sea surface temperatures form along the equator in the Pacific Ocean, specifically in the eastern to central Pacific.
The cooler water temperatures are caused by an increase in easterly sea surface winds. Under normal conditions these winds force cooler water from below up to the surface of the ocean. When the winds increase in speed, more cold water from below is forced up, cooling the ocean surface.
Think of it as a huge air conditioner. The temperature differences may only be a couple degrees Fahrenheit, but that's enough to redirect the subtropical jet stream. The jet stream channels storms northeast over the Hawaiian Islands, where they pick up moisture and warmth before heading into the Pacific Northwest.
Once over land, the jet stream connects with polar air streaming down from Canda and gives an extra punch to winter snow storms in the northern plains, the Pacific Northwest and Atlantic states.
The
U.S. Climate Prediction Center says that it sees the cool water conditions for the La Nina weather anomaly in the Pacific Ocean likely continuing into spring and possibly through the first half of 2009.
There's plenty of info on La Nina available via your favorite search engine, or you can visit the
NOAA for more info on the climate and weather than you ever thought you wanted to know.
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