Sea Fog over the Lake

Last December, many Chicagoans woke up to see wispy layers of fog rolling off of Lake Michigan. This is a fairly common weather event that happens when a mass of very cold air blows over warmer water, often called arctic sea smoke or sea fog. On this particular day, the air above the lake was 3 degrees and the water was 35 degrees.

When the cold air blows over the warm water, the water near the surface evaporates into the colder air above and increases the humidity in the air. When the air reaches its dewpoint, the vapor condenses into fog.

This phenomenon really only happens when there are strong winds driving the colder wind out over the lake. This weird effect can happen even if Lake Michigan is covered in ice .


http://www.chicagotribune.com/news/local/breaking/ct-lake-michigan-arctic-sea-smoke-htmlstory.html