Weather Words: Cold Air Damming

This segment originally appeared in today's edition of the Morning Brief newsletter. Sign up here to get weekday updates from The Weather Channel and our meteorologists.

Sometimes, cold air refuses to budge—even when warmer air is trying to take over. That’s cold air damming in action. This phenomenon occurs when a shallow layer of cold, dense air gets trapped against a mountain range, usually due to strong high pressure to the north. As warm air tries to move in from the south, it rides over the stubborn cold air below, creating a stark temperature contrast.

Cold air damming is most common along the eastern U.S., where the Appalachian Mountains act as a natural barrier. It often leads to dreary, damp, and chilly weather that lingers for days, even when nearby areas warm up. People in the Southeast commonly refer to this type of weather setup as “the wedge”. Around Atlanta in particular, that cold air gets “wedged” against the mountains and the north side of town will be cloudy, cool and miserable, while the sound side of town will be under blue skies and significantly warmer.

In winter, cold air damming can be especially dangerous, as freezing rain and ice storms become more likely when warm, moist air overruns the trapped cold air at the surface. That’s why it’s always important to take notice of weather watches and warnings, so you will be ready in case cold air damming makes for dangerous conditions where you live.

Jennifer Gray is a weather and climate writer for weather.com. She has been covering some of the world's biggest weather and climate stories for the last two decades.