We know how dangerous fog can be, but freezing fog makes it even more dangerous. Freezing fog occurs when those tiny water droplets that make up the fog freeze. As a result, everything the fog is touching freezes as well. Tree branches, roads, sidewalks, railings, vehicles will all end up with a thin coating of ice.

This can create black ice on the roads and make travel exceptionally dangerous. Not only will it be difficult to see because of the fog, but the roads will also be slippery. Black ice is when there’s a thin layer of ice on the roads that’s very difficult to see. It’s called black ice because it blends in with the rest of the dry roadway, making it nearly impossible to spot. A thin layer of ice can even form around airplanes, so de-icing will most likely take place if you are flying out of an airport that’s experiencing freezing fog.

The National Weather Service (NWS) will issue a freezing fog advisory if your area is impacted by freezing fog. In these instances, visibility is typically less than one mile.

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In 2022, a 30-car pileup in Washington state was most likely due to freezing fog. If you ever hear that freezing fog has developed in your area, it’s best to stay off the roads until the conditions improve.

This segment originally appeared in today's edition of the Morning Brief newsletter. Sign up here to get weekday updates from The Weather Channel and our meteorologists.

J​ennifer 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.