Analysis and Comments on a March 1998 Wedge Event
Cold-air damming along the Atlantic coast has been well documented in a paper authored by Gerald Bell and Lance Bosart (1988). Based on a 50-year climatology of cold-air damming, they found that the events peak in the months of December and March. In March, a split flow pattern develops as the westerlies retreat northward. Northern stream anticyclones are displaced further northward, and instead of air damming up along the west side of the Appalachians, the cold air spills southward on the east side of the mountains. A slow moving southern stream upper low will cause surface pressure falls southwest of the pressure rises associated with anticyclone, resulting in enhanced southward transport of cold air. The figure below shows a typical 500 and 850 mb synoptic pattern during a March cold-air damming event (Bell and Bosart). The upper two maps contain the 500 mb analysis, 12 hours apart; while the lower maps contain the 850 mb analysis. Notice how the northern stream upper trough pivots rapidly eastward and becomes negatively tilted, while the closed upper low over the southern plains moves at a much slower pace.
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