“The chief suspect behind the mysterious weather is an atmospheric pressure pattern called the Arctic Oscillation, which circles the high Northern Hemisphere. Its lower edge is known as the North Atlantic Oscillation (NAO). Together, the related features influence the path and strength of the jet stream. The jet itself is an air current that flows west to east across the northern latitudes of the U.S., Europe and Asia, altering temperature and precipitation as portions of it dip southward or crest northward. A strong jet stream that flows in a somewhat straight line from west to east, with few southward dips, prevents cold arctic air from drifting south. “The cause of this warm first half of winter is the most extreme configuration of the jet stream ever recorded,” according to Jeffrey Masters, a meteorologist who runs the Weather Underground, a Web site that analyzes severe weather data.”
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Jet Lag: What's Causing One of the Driest, Warmest Winters in History? The jet stream controls winter weather, but strange forces are controlling the jet stream this season
