What is Cold-Air Damming? Cold-air damming is when cold or cool moist air becomes trapped in the valleys on the east side of the Appalachian Mountains. Cold air is more dense than warm air, so it has a very hard time climbing over the mountain and settles in to the valleys. The cold air is pushed and dammed against the mountains. The cool moist air then helps form thick clouds over the cold air, blocking out the sun. This combination makes it very hard for temperatures to rise.
Central Pa saw this weather phenomenon Monday November 18th. High pressure was set up to the east of Pennsylvania. Winds around a high-pressure flow clockwise. The high brought cool moist air from the Atlantic Ocean to Central Pa. With winds coming out of the east the cool moist air settles into the valleys east of the Appalachian Mountains. When this occurs Blair, Huntingdon, Bedford and Centre counties are much cooler than the counties west of I-99.
Lets take a look at Monday’s high temperatures across the region.
Eastern Counties Western Counties
Huntingdon, Pa: 39 degrees. Indiana, Pa: 50 degrees
Altoona, Pa: 40 degrees Johnstown, Pa: 46 degrees
State College, Pa: 37 degrees Somserset, Pa: 48 degrees
Bedford, Pa: 39 degrees Pittsburgh, Pa: 51