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Why is it so hard to predict winter precipitation east of the Appalachians?

Forecasting winter precipitation can be tricky in many places, but particularly on the east side of the Appalachian Mountains, where shallow pools of very cold air can be forced south, forming a shallow layer of cold air beneath warmer air.  I’ve discussed this weather pattern, officially called “cold air damming” and unofficially “the wedge,” in previous blog postings.  I saw a good general description of why this weather pattern makes it so hard to make good predictions of precipitation type and amount online today.  You can read it at http://www.erh.noaa.gov/rnk/Newsletter/Winter%202004-05/P-Type.htm

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