So what exactly is cold-air damming? It’s when cold air is pushed up and dammed against a mountain chain like what we see here in Central PA. Cold air is denser (heavier) than warm air and it settles into the valleys. The cold air has a very hard time getting over the mountains.
Cold-air damming occurs when the winds come from the east. The easterly winds pick up cool and moist air from the Atlantic Ocean. The eastern counties are cloudier and quite a bit cooler. While the western counties are quite a bit warmer and even see more sunshine.
When it comes to freezing rain, how does cold-air damming play a role? The cold and moist air from the Atlantic settles in the valleys and forms shallow pockets of cold air. The rain doesn’t have enough time to refreeze back into sleet or snow because of how shallow the pockets of cold air are. The rain then freeze to ice when it makes it to the surface.