Winter Weather Awareness Week: How do we get different types of wintry precipitation?

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(WVNS) — Winter Weather Awareness Week 2021 runs from Nov. 15-19 in West Virginia as declared by Gov. Jim Justice. Throughout the week, your local StormTracker 59 team, alongside our partners at the National Weather Service and the West Virginia Emergency Management Division, will be providing important information on how to prepare for winter and its impacts on the “Mountain State”.

How do we get different types of wintry precipitation?

When dealing with precipitation in the winter, it’s all about temperatures. But not just what we’re seeing right at the ground. What we see fall greatly depends on how temperatures change from inside the clouds and down to the surface. Take sleet, for example. Initially, sleet starts out as snow, which melts after falling through a shallow layer of warm air that’s above 32F. After warming up enough to melt, it then falls through a much deeper layer of cold air, below 32F, and refreezes into little pellets of ice.

Freezing rain goes through a similar process, but this time the layer of warm air is either deeper or closer to the ground, causing the layer of cold air closer to the ground to be shallower. Since there’s not as much cold air available at the end of the precipitation fall, it doesn’t have enough time to become sleet before hitting the ground and instead falls as rain. Despite falling as a liquid, it can freeze on contact with the ground or whatever surface it falls on since they may be below freezing.

Cold Air Damming

Freezing rain and sleet are fairly common across West Virginia due to our unique topography. Due to the way the Appalachian mountains are aligned, they are more likely to deal with an issue known as cold air damming (CAD). Generally, CAD events happen when a strong area of high pressure is centered over the Northeast. Cold air will “wedge” itself in along the east coast and alongside the eastern slopes of the Appalachians.

Since cold air is denser than warm air, this wedge tends to sit close to the surface, creating a shallow pool of cold air. This is an ideal set-up for freezing rain or even sleet events if the cold air is deep enough. Generally, we see setups like this across Greenbrier, Summers, Monroe, Giles and Bland counties since they sit east of the Appalachians and Blueridge mountains. Though it is possible to see a similar set-up on the western side of the mountains through Nicholas, Fayette, Raleigh, Wyoming, McDowell, Mercer and Tazewell, it’s just not as common.

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