Winter Weather
Freezing Fog vs Frost: Icy Deposits, Visibility, and Slick Surfaces
How freezing fog differs from frost, why each forms, and when roads, bridges, trees, and sidewalks can become icy.
Quick answer: Freezing fog is made of tiny droplets that freeze on contact. Frost forms when water vapor deposits as ice on cold surfaces.
Freezing fog
Freezing fog reduces visibility and can coat roads, trees, signs, and power lines with ice.
It can create slick spots even when no rain or snow is falling.
Frost
Frost forms on surfaces that cool below freezing and collect ice crystals from water vapor.
It is common on clear calm nights when surfaces lose heat quickly.
Travel and plants
Freezing fog is more of a travel hazard, while frost is often a plant and surface-temperature concern.
Both can surprise people because the sky may look quiet.