Why Steam Fog Rises From Ponds in the Morning

A misty autumn morning on a beautiful pond. Andy Bennett/ MNN Flickr Group

The moody scene set by the steam rising off the surface of this sun-lit pond is a beautiful sight, and one that becomes more common when the weather shifts from warm summer sunrises to crisp, cold autumn mornings. The phenomenon goes by many names, including steam fog, evaporation fog, frost smoke and sea smoke. So what makes it happen?

Meteorologist Barbara McNaught Watson explains, "Bodies of water, such as lakes, ponds, and rivers, are much slower to cool down than land areas are. During clear fall nights, the warmth of the land escapes into space. As the air over the land cools, it will drift over the warmer pond. A thin layer of air above the pond is warmed by the pond water. Water evaporates from the pond's surface into this thin layer. The thin, warm, moist layer of air over the pond then mixes with the cooler air from the land. As it cools, condensation occurs and a fog forms. It looks like steam rising off the water, hence the name 'steam fog.' In the spring, the ponds are usually colder than the surrounding land. Just as they are slow to cool, they are also slow to warm."

This happens not only over bodies of water but even over moist surfaces, like dew-covered meadows or even over your own skin if you get sweaty while jogging on a chilly morning.

Now, next time you go out for a morning stroll along the edge of a lake or a pond and you see this happening, you can appreciate not only the beauty of it but also the science behind it!