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John Wheeler, WDAY, Published April 06 2013

Weather Talk: Arctic Oscillation switch allows cold-air intrusions

This spring has almost been the opposite of last spring so far: cold and snowy instead of warm and dry. The cause of any weather pattern is never single-faceted, but there is one large weather feature that is also in an opposite mode this spring compared to last year. This feature is called the Arctic Oscillation.

When the Arctic Oscillation is in its positive phase, there is a strong wind circulation around the higher latitudes and high pressure over the North Pole. This pattern tends to keep Arctic air locked away in the Arctic. In the negative phase, the Arctic circulation weakens, allowing frequent intrusions of very cold air farther south.

Last winter and spring, the Arctic Oscillation was positive. This January, the Arctic Oscillation switched to negative phase, and ever since our weather has been cold and frequently stormy.

Europe, also, has experienced much-below-average temperatures this spring along with areas of heavy snow.


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