NORFOLK, Va. — Cold air damming, or "The Wedge," is a term meteorologists use when a high-pressure system is “wedged” up against the Appalachian Mountains. Let’s break down what a wedge does.
The wedge typically occurs during the winter as a high-pressure system slides to the east and encounters the mountains. This can trap cold air on the eastern side of the range.
That’s because as the high-pressure system’s winds rotate in a clockwise motion, it draws colder air from the north down to the south. The cold air has no choice but to spill south, and often, it reaches the Piedmont and inland parts of our viewing area. The wedge causes conditions to become cloudy, foggy, and cool.
Cold air damming can complicate our forecasting. Sometimes, those cool and cloudy conditions don’t spread all the way to the coast. This can cause a significant temperature spread, where places inland can be as much as 20-30 degrees colder than cities around the coast!
Cold air damming is helpful in some cases though. On days when there’s the possibility for severe weather, if the wedge sets up in time, the cold air can limit the severe weather potential. The presence of cooler air decreases the atmosphere’s energy which is needed to produce thunderstorms.
Cold air damming also occurs on the eastern side of the Rocky Mountains. This layer of cold air near the surface can increase the chances of seeing snow in lower-lying areas. That low cloud deck we see in association with the "The Wedge" east of the Appalachians occurs often with "The Wedge" out west too.
That's how your weather works!