Weather Words: Black Ice

Some weather hazards are obvious when you see them. Entering snow- or water-covered roads, you know to take extreme caution and turn around if necessary.

But black ice is in a league of its own.

Black ice is one of the sneakiest winter hazards out there, and it’s exactly as dangerous as it sounds. It’s a thin, nearly invisible layer of ice that forms when moisture freezes on roads, sidewalks or bridges. Because it’s so clear, it blends in with the pavement beneath it, making it almost impossible to spot until you’re already sliding across it.

Black ice most often forms on calm, cold mornings or late at night when temperatures dip below freezing and the ground cools quickly. Bridges and overpasses are especially prone because they lose heat from above and below, freezing faster than the rest of the road. Even a light drizzle, melted snow or fog can be enough to create a slick, glassy surface once temperatures drop.

Drivers and pedestrians alike can easily be caught off guard. A road that looks merely wet can, in reality, be a skating rink. That’s why slowing down, avoiding sudden movements, and steering gently are key when temperatures hover near freezing.

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.