What's with these snowstorms? Natural patterns, plus randomness.
It’s a winter to remember – one that is likely to trigger a host of studies that try to tease out details of the factors contributing to the season’s snowstorms.
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The warm waters made their move during the fall, says Tony Barnston, the lead forecaster at the Lamont-Doherty Earth Observatory’s International Research Institute for Climate and Society in Palisades, N.Y. But only recently did stronger-than-normal thunderstorm activity move east of the international date line to begin rearranging atmospheric circulation patterns.Skip to next paragraph
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Jet stream a superhighway for storms
One result: The subtropical jet stream, a high-altitude river of air that snakes its way west to east across North America, is driven farther south than normal. The jet stream acts as a superhighway for storm systems that roar in off the Pacific.
The more-southerly average track allows storms to draw more moisture from the Gulf of Mexico as they move east, compared with storms crossing the continent farther to the north, adds Klaus Wolter, a researcher at NOAA’s Earth Systems Research Laboratory in Boulder, Colo.
In addition, El Niño has intensified the strength of the subtropical jet stream, pushing it to speeds of up to 200 miles an hour. That can translate into high wind speeds that the storms bring at ground level, he adds.
If El Niño’s atmospheric reach has enriched the moisture content of storms this winter, another atmospheric feature has helped ensure that more of that moisture falls as snow as the storms head east along the southern tier, then up the East Coast.
Seesaw pattern in atmospheric pressure
It’s dubbed the North Atlantic Oscillation – a seesaw pattern in atmospheric pressure between the northern and southern North Atlantic. It can vary on time scales as short as 10 day days, rather than remaining relatively settled over a season.
The NAO has been in a strong negative phase, which translates into colder-than-usual temperatures in much of the eastern half of the country, Mr. Barnston explains. That increases the temperature contrast between the chillier land and the Gulf Stream-warmed waters off the East Coast. That heightened contrast boosts the strength of the storm systems that travel up its length.
Others invoke the Arctic Oscillation, which is related to the NAO (indeed, some researchers hold that they are two names for the same phenomenon), as the engine driving colder temperatures deeper south this winter.
Either way, these two in concert have combined with El Niño – and a strong dash of random atmospheric actions – to make this a winter to remember.
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