Weather Words: Wedge

In everyday terms, the word “wedge” can mean to become stuck or forced into a tight space. In weather terms, “wedge” can be very similar. It's when clouds become stuck, or "wedged," up against the mountains.

In the southeastern United States, “the wedge” refers to a weather pattern formally known as cold air damming. It happens when a shallow layer of cool, dense air becomes trapped against the eastern side of the Appalachian Mountains.

The mountains act like a natural barrier, blocking the cold air from moving westward and allowing it to “wedge” itself southward along the eastern slopes, often from Virginia down through the Carolinas and into Georgia.

This setup typically forms when high pressure builds to the north of the region, sending cool, dry air down the eastern side of the Appalachians at the surface. At the same time, warmer, more humid air from the Atlantic or Gulf tries to move in above it.

The wedge can have a major impact on local weather forecasts. Temperatures within the wedge can be 10 to 20 degrees cooler than surrounding regions, and it can be stubborn to erode once it sets in.

Sometimes, it lasts for days, especially in the cooler months, until a front or stronger southerly winds push it out. For meteorologists and residents of the Southeast, “the wedge” is a familiar and often frustrating, or even dreaded, feature.

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.