If you have never heard of sea smoke, it may be because you don’t live in a colder region of the country. Normally, sea smoke, or steam fog, is only seen in the Arctic or Antarctic regions.
But with the extreme cold brought about by the Polar Vortex we experienced last week, the ambient air temperature in Duluth was hovering around -15 degrees Fahrenheit (-26 degrees Celsius) on December 18. And that is just what is needed to create the weather phenomenon.
Sea smoke is formed when very cold air moves over warmer water. It forms when a light wind of the very cold air mixes with a shallow layer of warm air saturated with moisture sitting right over the warm water. Now stay with me on this, and you will see how the thick fog forms, OK?
So that warm air right above the water is cooled well beyond the dew point, and this prevents that air from holding any more water vapor. So it condenses out, very similar to the way “steam” is produced over a hot bath or a hot cup of coffee.
Sea smoke, while it may be thick as all get out, usually doesn’t rise very high. Most of the time, lookouts on ships can see over the steamy mass, but small boats will be engulfed in the fog, making it difficult to navigate.
This is what happened in Minnesota on December 18 when the much colder air collided with the much warmer waters of Lake Superior and that layer of warmer air right over the waters of the lake. While the temperature in Duluth hit -17 degrees F, the coldest place was Embarrass, coming in at -38 degrees F.
