Consider walking by a large body of water on a cold day. The water itself might not be frozen. However, there is a steam coming up from the water. It might look like the perfect backdrop to a horror movie. Steam coming up from the water on a cold day, whether it’s Lake Erie, the Arctic Ocean, or your local pond, it is all the same phenomenon.
Aptly, this is known as steam fog. This is a type of fog that takes place in cold weather over open water. What happens is cold air will sweep over a relatively warm body of water (relative being the key word here). In the case that a body of water is not frozen, the cold air mixes with relatively warm air just above the water. The air just above the water is cooled to the point where it condenses, known as the dew point.
In the Arctic regions, steam fog is called “sea smoke”. The concept is the same. A relatively warm pocket of air sitting just over the water, mixing with cold air, with condensation being the result. In the case of sea smoke, this involves the ocean, a saline body of water. With salty ocean water, the temperature required for water to freeze is considerably lower. And with markedly colder air temperatures, sea smoke will form in open stretches of water, wherever there isn’t sea ice.
Steam fog (or sea smoke) is quite common in the Arctic and Antarctic regions. The saline properties of the oceans combined with very cold temperatures make this possible. It isn’t as common in regions with milder climates. However, it can happen with the right conditions. Steam fog has occurred over the North American Great Lakes.
It can also occur over ponds, as this video from Huntsville, AL will show.
In this particular video, this pond has its source from a nearby spring. This likely plays a factor as to why it’s 17 degrees Fahrenheit outside, but the water isn’t frozen. Steam fog is forming over the pond. With the local hydrology aiding in the water keeping a relatively stable temperature (karst topography), steam fog was able to take place. In the case of a spring, water temperatures are more stable. For this reason, the water wasn’t frozen.
Geography plays a role in where steam fog (also known as sea smoke) is found. It is found more often in the higher latitudes. A combination of a very cold climate, and ocean water freezing a lower temperatures than fresh water, this plays an important role. Steam fog can form over lakes in relatively temperate regions if the water isn’t frozen and the temperatures are cold enough. It can also take place over bodies of water fed by springs, given a relatively stable water temperature. And thus geography plays a role in local weather.