Freezing fog is not really a meteorological term, Pearson said. In order for it to form you need items or an object near the surface to be below freezing temperature, he said. This could include, trees, power lines and power poles, fences, tall weeds or cars. The air above the ground has supercooled water droplets in it, that might be just below freezing but are still in liquid form.
Once those droplets come in contact with something at the ground or just above the ground freeze on contact with the surface of that object, Pearson said. Most often, freezing fog does accumulate on trees and power lines and if the wind is calm or maybe even light, can make a very picturesque scene as the supercooled water droplets turn into ice crystals (also called rime ice). If there is some wind, then the water droplets will just form more as a hard layer of ice vs the more crystalized picturesque rime ice.