What is "hoar frost"?

Hoar frost refers specifically to ice crystals that form on cold surfaces, typically during clear, calm nights when the temperature drops, and moisture from the air condenses and freezes. The process occurs when the air is saturated with moisture, and the temperature of surfaces—like grass, cars, or trees—falls below the freezing point, allowing the moisture to deposit as ice crystals. This common meteorological phenomenon often leads to the formation of intricate frost patterns and can create a picturesque winter landscape.

The formation of hoar frost is not related to snow directly or the conditions under which sleet falls, nor is it linked to fog that occurs due to high humidity, which involves condensation in the air rather than on surfaces. Thus, understanding that hoar frost is specifically about the freezing of moisture on cold surfaces is essential in distinguishing it from other atmospheric phenomena.