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In early December 2009, the Arctic Oscillation entered a strongly negative phase that persisted through early January 2010, and then redeveloped in February. Arctic air maintained higher pressure than lower latitude air masses, allowing the frigid air to push southward. This image shows temperatures for February 1-11, 2010 as the departure from average for the same dates from 1971-2000. The Arctic was warmer than average (red colors) while most of the mid-latitude regions around the world were colder than average (blue colors). NOAA image courtesy of Ned Gardiner, Climate Program Office, and Michelle L’Heureux, Climate Prediction Center.