Fog Types

Fog Types
Formative Process	Fog Type	Details	Example
Cooling	Radiation = Ground = Valley	Forms on clear, cold nights at ground level. Most common in late fall and winter. Slight breeze (< 5 knots) enhances formation. Strong breezes disperse. Thickest around sunrise. Often "burns off" during day. Tends to occur during air stagnation associated with high pressure, especially in valleys.
	High-inversion	*Also known as stratus fog* or high fog. Occurs when radiation fog lifts slightly during the day.**
	Advection	Occurs when warm moist air moves over a cooler surface and is chilled. Common as a coastal fog over cold water (Pacific Coast). Also occurs over land, especially during the winter. Occurs over the open ocean along boundary between cold and warm currents.
	Upslope	Forms when moist air rises to flow over a hill, mountain or elevated plain, common along Wasatch Range.
	Ice	Particles are ice grains, not water droplets. Requires very cold temperatures, about -40°F or lower.
Evaporation/ Mixing	Steam	Occurs when two different unsaturated air masses mix, producing a saturated air mass. Seen when cold air moves over warmer water, e.g., over lakes, streams, even puddles or wet roads and sidewalks. The fog type associated with "seeing one's breath."
	Sea Smoke	Steam fog over the ocean or a large lake.
	Frontal	Produced by warm rain falling through colder air. Like steam fog except raindrops, not a body of water, is the warm water source. Especially common ahead of a warm front.