GREENVILLE, N.C. (WNCT) — Have you heard of cold air damming, or ‘the wedge’? Either term may sound familiar, probably because it’s a very common phenomenon right here in North Carolina.
Cold air damming develops when a low-level cold air mass is trapped on the eastern side of a mountain and a high pressure system is situated to the north. High pressure spins clockwise, meaning the chilly northerly winds have an eastward component.
For North Carolina, these easterly winds push up against the Appalachian Mountains. The frigid, dry air is much too dense to flow over, creating a pool of cold air on the eastern side of the mountains. The northerly winds continue to push cold air south along the mountain range’s spine, creating a pocket of cold air at the surface, also known as ‘the wedge.’
When the cold air mass is exceptionally deep or strong, the wedge can be evident all the way to the Coastal Plain, as far west as Central Alabama, and as far south as Tallahassee, Fla.
Carolina’s Piedmont region experiences cold air damming year-round, with the strongest events occurring in the winter months. When warm air rises over the pool of cold air, it creates thick cloud cover and not only allows for colder temperatures, but freezing rain like many locations in Central and Western North Carolina experienced this winter. The wedge creates huge temperature gradients which are very apparent across the state.
Cold air damming is a complex weather phenomenon that’s pretty tricky for us meteorologists to forecast. But, next time you see that wedge of cold air dipping down into the Carolinas, you’ll know exactly what’s happening.