Steam fog
Steam fog, also called sea smoke or evaporation fog, forms when relatively warm water supplies moisture to much colder air immediately above it. The moisture condenses into visible droplets, producing shallow wisps that often resemble smoke rising from a lake or sea. It differs from sea fog, which generally forms when warm, moist air moves over colder water.
Formation
Air just above a water surface can take up water vapour through evaporation. If much colder air lies over the water, the added moisture cools and condenses into tiny suspended liquid droplets; these droplets make the plume visible. This process is often termed evaporation-mixing fog. The visible tendrils are therefore condensed droplets, not smoke, and the initial water vapour itself is invisible.
Conditions and appearance
Steam fog is favoured by a strong temperature contrast between water and overlying air. It is commonly reported in cold seasons over comparatively warm lakes, rivers, bays, or open patches of water among sea ice. The fog is often shallow: a stable temperature inversion can limit vertical mixing and confine the moisture near the surface. Wind and mixing affect how rapidly the wisps are dispersed, so the phenomenon may appear in shifting patches rather than as an even blanket.
Distinction from sea fog
The terms can be confusing. Steam fog forms as moisture is added to cold air above warmer water. By contrast, sea fog is commonly an advection fog: moist air travels over a colder water surface and is cooled toward saturation. Both obscure visibility over water, but the temperature and moisture pathways differ. The National Weather Service glossary describes steam fog as water vapour added to air much colder than its source, while defining sea fog as moist air transported over cold water.
Geographic occurrence and practical importance
The process can occur over fresh or salt water wherever cold air passes over relatively warmer water; it is especially associated with polar and northern settings, but smaller events also occur over inland waters in autumn and winter. In steep-sided coastal terrain, fog can sometimes drift beyond the shoreline. Like other fog, it can sharply reduce visibility, so its appearance matters to navigation and aviation. Forecasting depends on air and water temperatures, moisture, stability and wind rather than on a single universal threshold.
Key facts
- Common names
- Steam fog is also known as sea smoke, evaporation fog, steaming fog, or Arctic sea smoke in some contexts.
- Basic mechanism
- Evaporation adds moisture to cold air over relatively warmer water, and the moisture condenses into visible droplets.
- Typical structure
- Steam fog is often shallow, especially when a stable inversion restricts vertical mixing.
- Not the same as sea fog
- Sea fog commonly forms when moist air is cooled by passing over colder water; steam fog involves moisture entering colder air from warmer water.
- Visibility
- Steam fog may reduce visibility over water and can drift onto nearby land in some settings.
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References
- 1.Steam Fog
SKYbrary Aviation Safety · other · reliability: unverified · retrieved 28 October 2026
Supports: Describes names, formation, typical shallow structure, inversion conditions, locations and contrast with advection fog.
- 2.NOAA's National Weather Service - Glossary (Fog)
National Weather Service, National Oceanic and Atmospheric Administration · other · reliability: unverified · retrieved 28 October 2026
Supports: Defines fog, steam fog and sea fog, including the distinction between adding moisture to cold air and transporting moist air over cold water.
- 3.A. Fog Types
National Weather Service, Houston/Galveston Weather Forecast Office · other · reliability: unverified · retrieved 28 October 2026
Supports: Meteorological guide describing steam fog in northern and middle latitudes, the role of inversions and fog forecasting factors.
- 4.Cold Enough? The science behind sea smoke
Maine Sea Grant, University of Maine · other · reliability: unverified · retrieved 28 October 2026
Supports: Explains sea-smoke formation over warmer water in cold air, how wind and temperature contrast affect it, and coastal observations.
- 5.A Coupled Model Study on the Formation and Dissipation of Sea Fogs
Monthly Weather Review, American Meteorological Society · other · reliability: unverified · retrieved 28 October 2026
Supports: Peer-reviewed coupled-model study that includes steam-fog formation and dissipation, including air-water interaction.
References are suggested by the research engine and may be incomplete. Unverified URLs are omitted rather than guessed.
Article history
- Version 128 October 2026 · EditorCreated by Zapia