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Posted at 11:45 AM ET, 03/25/2010

Now you know the power of El Niño

By Don Lipman

* Rain moving in tonight: Full Forecast *

373_snowstorm20100205.jpg
Satellite image of the Snowmageddon storm of Feb. 5 that dumped 16-32" of snow across the area. Note the moisture feed extending into the Pacific ocean. Image courtesy NOAA's Environmental Visualization Laboratory.

A couple of years ago, when the mid-Atlantic was in a snow drought, I noticed a comment on one of the weather blogs from someone who said that as a child, he remembered that old-fashioned northeast snowstorms seemed to originate with low pressure centers in or near the Gulf of Mexico which would then come up the Atlantic Coast. Of course, it hadn't been that long; it just seemed so, because nor'easters were few and far between during that period.

This past winter we had more nor'easters or quasi-nor'easters than I can count or ever remember in one season. What was the reason? Yes, you can blame it on a negative NAO (North Atlantic Oscillation) and a negative AO (Arctic Oscillation), both known contributors to a colder- and stormier-than-normal pattern in the eastern U.S. Some meteorologists may even correctly implicate other hemispheric systems, but it was probably ENSO, the El Niño Southern Oscillation, that was the coup de grâce for the ferocious mid-Atlantic winter.

Keep reading for more on this past winter's El Niño...

And it was not just any El Niño. It was a moderate-to-declining one that may have tipped the scales in favor of Snowmageddon, because had the El Niño been as strong as, for instance, that of the winter of 1997-98, it probably would have overwhelmed the negative AO and NAO influences, repelling the polar jet stream (which supplied the cold air for these storms) much farther northward. For those of you who remember, the winter of 1997-98 was exceptionally mild and almost snowless; the El Niño's southern stream produced many storms but there was little cold air.

The El Niño-influenced southern stream jet that traversed the country this past winter just kept going....and going....and going, just like the Energizer bunny. Every few days, it seemed, it would spawn a new storm to take shape somewhere in the Gulf region which would then head toward the Carolinas and become the catalyst for yet another mid-Atlantic and/or Northeast snowstorm.

But the impact of El Niño goes far beyond the formation of nor'easters or the lack thereof. Aside from its widespread influence on parts of the Far East, Australia and South America, it often has major effects -- some good, some bad -- on the western U.S., particularly the West Coast, as we've seen in recent months. The Russians have even blamed El Niño for an unusual two-foot Moscow snowfall this past February. (Moscow's Mayor Yury Luzhkov had previously promised to prevent snow from falling ever again in Moscow......If he was given enough money for the Russian Air Force to seed the clouds outside the city.)

In a typical El Niño winter, the constant moisture supply from the "Pineapple Express" causes landslides and mudslides in California (we've seen that); strange desert "blooms" in the desert Southwest (some evidence of that, too); and incessant rains, even snows, across the deep South (plenty of that, too). If all this weren't bad enough, the unheralded moisture and resulting explosive desert plant growth can cause a sudden increase in the insect and grasshopper population, with a bumper crop of rodents to follow. The rodents, of course, breed all sorts of disease, particularly Hantavirus Pulmonary Syndrome (HPS).

On the other hand, during an El Niño the heavy mountain snows, although responsible for an increased risk of avalanches, are welcome news for many of the western states, which greatly depend on the mountain snowpack's water content. And the past winter's snows couldn't come soon enough for California's Sierra, for instance, where there's been three years of drought. Even so, despite the relentless storminess, recent surveys have shown that the snowpack's water content is only about 7% above average and many California lakes are still well below capacity.

So when will the next El Niño occur? Since we're still coming out of the present one, it's a little early for NOAA's predictions, but one thing's for sure: we'll have plenty of advance notice with the help of satellite measurements and an extensive data buoy system which, together, track Pacific sea surface temperatures. This network, developed mainly after the huge 1982-83 El Niño will help to prepare us all.

By Don Lipman  | March 25, 2010; 11:45 AM ET
Categories:  Education, Lipman  
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Comments

Thanks for this. I think we had around 8" (rain equivalent) for December. That is a lot. We've had spring and summer months were we get 8" but the heat and evaporative effects cause a lot of the moisture to not saturate the ground. Not so this december. What's the lull period btw el nino's I want to enjoy our dry winters while i can.

Posted by: jojo2008 | March 25, 2010 8:36 PM | Report abuse

By contrast, many of our recent El Nino's have been free of snow, but often wet and windy [1997/98]. The other strong El Nino [1982/83] of recent memory featured one very big snowstorm.

Probable explanation: The AO and NAO must have been largely positive during these El Nino's.

Posted by: Bombo47jea | March 25, 2010 11:24 PM | Report abuse

jojo2008: On average, El Nino's seem to occur about every 3 to 7 years. Obciously, some are much more potent than others.

Don, Capital Weather Gang

Posted by: Weatherguy | March 26, 2010 1:23 PM | Report abuse

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