What conditions make up an ice fog?

Ice fog typically occurs under very specific atmospheric conditions characterized by very cold temperatures combined with high humidity. When the air temperature drops significantly, particularly below -20°F (-29°C), and the humidity is relatively high, this can lead to the formation of tiny ice crystals suspended in the air. These ice crystals are what create the "fog" effect, as they scatter light and can significantly reduce visibility.

The process involves the water vapor in the air condensing and freezing directly into ice without passing through the liquid phase, which is a phenomenon known as deposition. The combination of extremely low temperatures and moisture in the air is essential for ice fog to develop, making it distinct from typical fog formations that occur at warmer temperatures.

In contrast, other atmospheric conditions such as moist warm air cooling rapidly or cold air in contact with warm ground do not produce ice fog because they fail to maintain the extreme cold combined with high humidity necessary for ice crystals to form. Similarly, mild temperatures with heavy rain would not lead to ice fog, as the warm conditions would prevent freezing and the formation of ice crystals.