Meteorologists would like nothing better than to be able to tell you in no uncertain terms about the causes and effects of major weather events, but the truth is, day in and day out, the system they are trying to describe behaves more like a pinball machine than a finely-tuned watch.
There is no simple explanation for the storm that is about to hammer the big population centers of the East Coast.
(Click on this image from a National Weather Service forecasting model and watch how the latest forecast plays out.)
Meteorologically, what is about to happen can be classified as a "bomb" -- an episode of very rapidly falling air pressure -- in this case, as much as 35 millibars in 24 hours. Two low-pressure systems are flowing together. A "motherlode" of arctic cold is riding down on one jetstream and a bank of warm tropical moisture is riding up on another -- circumstances that portend high winds, heavy snow, white-out conditions, a blizzard, and perhaps even thunder amidst it all.
It is true that the presence of El Niño conditions in the tropical Pacific Ocean tilt the odds in favor of more winter snowstorms along the East Coast. Statistical studies show this to be the case for the mid-Atlantic region, but the differences are not great, and in the Northeast there is no difference at all.
It is difficult to imagine circumstances of extremely heavy snowfall without the extra rich flow of tropical moisture supplied by El Niño -- but it's not impossible. Last week's big snow-laden blizzard that buried Washington approached snowfall records set by the "Knickerbocker Storm" that killed 98 people when the roof of a DC movie theater collapsed. That storm struck in late January 1922 -- a year when there was no El Niño.
Among the more typical impacts of El Niño on the northern half of the country are warmer winter temperatures than usual, but the New Yorkers I know probably aren't going to remember this particular season for its warmth.
Winter seasons, and El Niño episodes, come in a lot of flavors. There is enough natural variability to winter -- especially in the eastern half of the United States, where continental, polar Arctic air confronts flows of warm, oceanic moisture -- to confound statistics that are based on too few years, too few El Niño episodes, and too few winter storms.
It is not just the imperfections of science, it is the very nature of the beast. I remember an El Niño expert facing a barrage of questions from news people who wanted to know exactly when and where and how the big 1997-98 El Niño was going to make itself felt. Finally, he threw up his hands. "Ladies and gentlemen," he exclaimed, "the atmosphere itself does not know what it is going to do next week!"
Tags: Geophysics, Meteorology, Winter
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