Frost forms when water vapor freezes straight onto a cold surface as tiny crystals.

The longer version

Frost skips the liquid stage entirely. When a surface cools below both the dew point and the freezing point, water vapor in the air touching it turns directly into ice crystals through deposition, and the crystals grow outward in branching, feather-like shapes.

It appears on clear, still nights when objects such as blades of grass, window panes, and metal railings lose heat rapidly to the sky. Light winds or cloud cover usually prevent it. A thicker coating known as hoar frost builds up when cold, humid air persists for many hours against the same surface.

Where this entry sits

Clouds, wind, rain, and storms shape daily life in ways that most people barely notice. This collection explains snow, lightning, rainbows, the turning seasons, temperature, the instruments forecasters rely on, and scraps of old weather lore. The full list sits on the Weather and Climate page, where every entry is listed in order.