We get frozen fog in the outer west Portland Metro area a lot, in rock creek and the more rural areas it's common. It's fog that exists at the edge of freezing temperatures, so that the fog develops, drifts down onto something as a small droplet and freezes there, it's so light that it can drift upward on the lightest breeze and stick to the undersides of things. Think light snow that coats every single surface (including the undersides of leaves), instead of just the tops of things through gravity. It will take a normal landscape and create a pure completely white winterscape in the matter of an hour - whiter than you get during heavy snowfall because of the non-gravity induced sticking nature of it.
Freezing fog is different than "Ice fog", which is where the air is so supercooled that the fog is literally a cloud of ice crystals. Freezing fog is just normal fog that freezes on contact, or freezes then falls onto things.
:thumbup: