In summer, steam forms off of the Chattahoochee river in Atlanta almost daily:
- Temperature of the river is colder than the air;
- Air is already at 99% relative humidity;
- Air near the water gets cooled by the water;
- Therefore there's a layer of fog about 10-20ft (3-6m) above the river.
In contrast, the opposite is happening here: the air above Lake Michigan has a dew point so low that the evaporation results in air that is already maxing out the amount of moisture that it can handle at that temperature. More precisely, the air immediately above the water can handle the moisture since it is closer to the temperature of the lake; but as it mixes with the colder air further from the surface, the dewpoint is lower and the moisture condenses.
- Temperature of the river is colder than the air;
- Air is already at 99% relative humidity;
- Air near the water gets cooled by the water;
- Therefore there's a layer of fog about 10-20ft (3-6m) above the river.
In contrast, the opposite is happening here: the air above Lake Michigan has a dew point so low that the evaporation results in air that is already maxing out the amount of moisture that it can handle at that temperature. More precisely, the air immediately above the water can handle the moisture since it is closer to the temperature of the lake; but as it mixes with the colder air further from the surface, the dewpoint is lower and the moisture condenses.
Either way, the effect can be beautiful.