America

Extreme Snow, Rain This Winter All El Nino's Fault

The winter storm heading to the East Coast this Super Bowl weekend, a weather system expected to drop nearly two feet of snow in the Mid-Atlantic region, is all about El Nino.

Accuweather's Jack Boston does a good job of explaining how the El Nino-related jet streams coming out of the atmosphere above the Pacific Ocean are going to cause what some wags are calling Snowpocalypse. (Or maybe Snowpocalypse 2 since we in Washington, D.C. got nearly two feet of snow right before Christmas.) He's got some really informative maps that many a weather geek like myself will appreciate.

Meanwhile, All Things Considered had a more lengthy explanation of the El Nino factor this year. For instance, NPR's Christopher Joyce explains that the North American continent is getting the weather it is because we're seeing the strongest El Nino pattern we've seen in a little over a decade.

For instance, the last really strong El Nino year was 1997-1998. Interestingly, the East Coast didn't get a big blizzard during that period. It was actually 1996, a non El Nino year, when we were hit by a massive blizzard that extended from the Mid-Atlantic into New England, paralyzing the region for days.

Anyhow, here's a key excerpt from the NPR.org version of Chris's story:

Scientists knew last summer that this was going to be an El Nino year. But it wasn't until the winter that its effects really hit the United States.

The strong El Nino and the subsequent precipitation are a result of something that started thousands of miles out in the Pacific Ocean.

"Ocean temperatures across the equatorial and tropical Pacific Ocean are somewhere upwards of two degrees above average," says Mike Halpert, deputy director of the Climate Prediction Center at the National Oceanic and Atmospheric Administration. "So we have had what we would characterize as a strong El Nino."

Scientists at the center say this is the strongest El Nino since the winter of 1997-98. What happens is that unusually warm sea surface temperatures in the western Pacific move east. That changes the heating pattern of the atmosphere, which in turn pulls the Pacific jet stream farther south. A jet stream is a fast and narrow current of air that travels high up in the atmosphere.

"And that jet stream is where we see a lot of storminess typically," says Halpert. "And we saw a very classical case of that, a superstrong jet extended all the way across the Pacific with storms impacting California one after the other."

A strong El Nino also alters another jet stream nearer to the equator that brings more storms to the Gulf area.

In fact, a strong El Nino plays havoc with weather from Indonesia to the Atlantic, but in different ways. Indonesia gets unusually dry weather, and in fact fires in parts of Indonesia have been frequent recently. Peru, on the west coast of South America, tends to get what California gets — flooding rains.

Halpert says storms are local events and no single storm can be attributed directly to the phenomenon. "One way to think of it is that El Nino conditions the atmosphere for these types of storms," he says.

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