why do we have fog
Fog happens when the air near the ground cools enough, or gets moist enough, that water vapor turns into tiny suspended droplets, essentially creating a low-level cloud around us.
What fog actually is
- Fog is basically a cloud that forms at ground level rather than high up in the sky.
- It is made of countless tiny liquid water droplets (or ice crystals in very cold conditions) floating in the air, which scatter light and make everything look hazy.
The core ingredients
- High humidity: Fog tends to form when relative humidity is near 100%, meaning the air is holding as much water vapor as it can at that temperature.
- Cooling of air: When warm, moist air cools down to its “dew point,” water vapor condenses into droplets and fog appears.
- Condensation nuclei: Dust, salt, and pollution particles give water vapor something to cling to, helping droplets form and making fog thicker in some areas.
Main ways fog forms
- Radiation fog
- Forms on clear, calm nights when the ground loses heat and cools the air right above it until condensation occurs.
* Common in valleys and open fields, often appearing around dawn and then fading as the sun warms the ground.
- Advection fog
- Happens when warm, moist air flows over a colder surface (like cool ocean water or snow-covered land) and is chilled to its dew point.
* San Francisco’s famous summer fog is a classic example, with cool Pacific air moving inland.
- Evaporation (steam) fog
- Occurs when cold air passes over warmer water or moist ground; water evaporates into the colder air, then quickly condenses into fog.
* Seen over lakes, ponds, and even heated swimming pools on chilly mornings.
Why fog seems to “appear” and “disappear”
- Fog can roll in quickly because small changes in temperature or moisture can suddenly push the air to, or away from, saturation.
- It does not literally “burn off”; instead, sunlight warms the ground, drier air mixes in, droplets evaporate, and visibility improves from the edges inward.
Information gathered from public forums or data available on the internet and portrayed here.