We saw plenty of it this morning across the Carolinas, but what exactly is freezing fog?
In a regular fog situation, you have millions of tiny water droplets suspended in the air, like a cloud at the Earth's surface. Freezing fog obviously forms when temperatures drop below freezing. In this case, the droplets are still water, but they are made of supercooled droplets - liquid water whose temperature is below freezing.
It doesn't turn to a solid because liquid water needs something to freeze onto. And it does as soon as it comes in contact with a below freezing surface, like your car windshield or even the roadway.
While freezing fog won't cause measurable accumulation, it can provide a glaze over cold surfaces and make them slippery enough to cause roadways or sidewalks to become slick.