Cold Air Damming We had another example of cold air damming Tuesday. Just what is cold air damming ? It is when a shallow layer of cold air becomes entrenched or dammed up against the eastern slopes of the mountains. This is a phenomenon particular to East Coast from central Pennsylvania to northern Georgia and all points in between that lie in the piedmont east of the Appalachian Mountains. Colder air is more dense than warm air. The wedge of cold air sits up against the mountains and warmer air aloft boosts temperatures from 2000’ and higher well above freezing but that shallow layer remains below freezing. The warmer air blows over the mountains but never scours out that shallow layer of cold air. As a low pressure system tracks to our west it drags a warm front up the eastern seaboard. This warm front begins to buckle as it moves into cold air. The configuration of the warm front looks like a big letter ‘U’. The front moves through Charleston, WV and then dips south to Richmond then curves back northeastward up along the Bay or in the Delmarva. More often that not by the time the warm front pushes through the last vestiges of cold air the trailing cold front moves through so quickly we never warm as much as our neighbors in the mountains or to our east. Charleston, WV could be 47 degrees while National is stuck on 32 degrees and Salisbury is 52 degrees. When forecasting a cold air damming situation we must always remember that the cold air hangs on at least twelve hours after the computer guidance thinks it will.  ¶ 12:51 AM