(WGHP) — Sometimes, we like to see a cool northeast wind, especially during the hot, muggy days of summer. But in fall and more so in winter, a northeast wind can really send a chill through your body. It can also drastically change what you see falling outside of your window.
In winter, meteorologists in North Carolina are always looking out for “the wedge.” If you don’t like the term, you can call it the “Appalachian Wedge” or its scientific name, “cold air damming,” or CAD.
What is the ‘wedge’?
So, what is cold air damming or CAD? The classic situation involves a high-pressure system over the northeastern United States. During the cold weather season, high pressure with its northeast wind sends cold air into North Carolina. The cold air is then banked or dammed against the Appalachian Mountains. Now we have a chilly and cloudy day.
Sometimes “the wedge” can stay in place for a day or two. Or it can remain in place for several days! This is when meteorologists develop severe headaches because it’s tough to determine when “the wedge” will break.
Given time, the cold air normally breaks across the Coastal Plain and the Mountains. But the Piedmont is located in the “sweet spot” of the damming region. Often, we are the last ones to see sunny skies and warmer temperatures.
Sometimes when the dam breaks, you can end up with some wild temperature swings. It can be 60 degrees in Asheboro and Burlington, while it’s 40 degrees in Greensboro and Winston-Salem with even colder temperatures north and west of Greensboro and Winston. Even stranger, places like Boone can be warmer than the Piedmont during wedge events.
What kind of weather does the wedge bring?
Cold air damming can also play a role in the type of weather we see. Most of the time, “the wedge” brings us cloudy skies and some mist and drizzle. But if other systems like low pressure or a cold front get involved during the cold weather season, this is when it really gets fun. Will we see rain? Will it snow? Or will the Piedmont end up with a sloppy wintry mix?
Cold air is dense and heavy. It will sink to the surface and push the warmer air above it. That’s why we end up with mist and drizzle.
But if something stronger arrives, like a low-pressure system moving across the Gulf Coast states, this is when snow becomes possible. The low is tapping into a moisture source and bringing precipitation into our cold air.
If high pressure across Pennsylvania or New York state remains in place, the cold air will remain in place, and the snow will continue to fall. But if the high starts moving out of the way, the cold air will also move out of the way. The snow will begin to change as milder air takes over, leaving the Piedmont with a mess of snow, sleet, freezing rain and then rain.
Of course, as the transition starts, you cut your snow totals. That’s why normally you see lighter snow amounts across the southern Piedmont, where the mild air arrives first, and greater snow totals along the Virginia border, where the cold air hangs in longer. Timing this transition can be difficult, but who doesn’t like a challenge?
CAD can also factor into severe weather. “The wedge” front can be a barrier between hot, muggy air and cool, stable air. Sometimes along the barrier, thunderstorms can grow and interact with the warm south winds and the cool northeast winds. Changing wind directions can bring spin and sometimes tornadoes.
Forecasting North Carolina weather is never easy, and it’s tough to understand. Meteorologists can say a lot of words that leave your head spinning. Hopefully, this article will provide you with a better understanding of some of the weather hurdles and some of the terms we use.