Science: The Cause of the Snow

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Particularly in the East, the frozen, snow-strangled U.S. last week could only echo General George S. Patton's exasperated wartime injunction to his chaplain: "Goddam it, get me some good weather!"

Not since Dec. 1 had the cities and farms east of the Mississippi seen even reasonable winter weather. Ferryboats froze in Lake Michigan. Georgia peach trees shivered in the coldest winter in 25 years. New York City, buried under 55.7 inches of snow that had fallen this season, also endured 16 days of continuously below-freezing temperatures. Last week, in a taxi driver's dream of heaven, private cars were banned in Manhattan for five days to facilitate snow removal, which so far has cost the metropolis some $20 million.

To millions, there was only one urgent question of the moment: Why this miserable weather? In Washington, even as quarter-sized snowflakes floated down outside his window, U.S. Weather Bureau Meteorologist Jerome Namias had an explanation that did not rely on an analysis of sunspot cycles, lowered ocean levels, or industrial fumes. The immediate cause of the weather: the planetary winds were wandering.

During a generally mild November, said Namias, the planetary winds (which generally circle the earth from west to east) flowed in a steady river of air 10,000 ft. to 50,000 ft. above the earth. This was normal. But the longer the river flowed unperturbed, the more certain was its eventual breakup into meandering, undulating waves that swirl north and south, mixing arctic and tropic air. Early in December, that happened. A cascade of cold air swept toward the Gulf of Mexico at the same time that the warm air was sucked into the heart of the continent. The heavier cold air swung under the belly of the warmer wind, lifting it, cooling it, and turning the entire moisturized mess to snow.

Even as the transformation was taking place, low-pressure areas were created, drawing down more cold air from the north and intensifying the temperature contrasts. To aggravate the storm cycle further, the snow itself reflects more sunlight back into the atmosphere, prevents the ground from warming, and touches off the start of a four-to-seven-day feedback loop that helps create the conditions for the next snowfall.

While the Eastern U.S. was blanketed by layers of snow, said Namias, Alaska has been abnormally warm, while Europe and the Atlantic Ocean have been stormy. "But," he added with a touch of meteorological pride, "the abnormalities in North America equal or exceed any in the world." And how long will it last? Said Namias helplessly: "Ultimately the vicious circle will break as the sun moves north in the sky, warming the arctic air mass. Until then, this pattern is likely to stay around for a while."