What is called when water vapor changes directly into ice crystals on contact?

The phenomenon where water vapor transitions directly into ice crystals upon contact with a colder surface is known as frost. This process is a type of deposition, where vapor does not first become liquid but instead forms solid ice, typically occurring in freezing conditions. Frost typically forms on surfaces like grass, leaves, and cars during the night when temperatures drop and water vapor in the air comes into contact with those cold surfaces.

Dew refers to liquid water droplets that form when water vapor condenses onto a cooler surface, so it involves a liquid phase which frost does not. Condensation is the general process of water vapor turning into liquid, which again does not involve the solid phase. Frozen mist is not a commonly used term in meteorology, and while it might suggest some combination of conditions, it doesn’t accurately describe the direct transition of vapor to ice crystals. Thus, frost is the precise term for this specific change of state.