Recipe: take one cup of boiling water and throw it out in the cold.
Steam fog is a favourite topic of the Kootenay Lake website. There is a page dealing with Steam fog over the Lake, one about Steam fog over land, and a discussion of vapour mixing as one of the two condensation mechanisms leading to clouds and fog. Steam fog has also been treated twice before in this blog: Sprites, dogs & devils; and Delights of steam fog.
Despite presenting numerous pictures and discussions of steam fog around the Lake, I had never before seen the little demonstration offered here: produce a steam fog by tossing boiling water outside on a really cold day. I learned of it from a friend in Pennsylvania, who learned of it from a correspondent in Brazil, who learned of it from a video doing the rounds in Brazil: Agua a ferver com uma temperatura a 30º NEGATIVOS (roughly: throw boiling water at a temperature of -30°C). I found the video on Youtube. When I tried the experiment this morning, the temperature was only -5°C, and the result is not as spectacular as shown on the video, but it was easier to see what is going on.
In the first picture, freshly boiled water is tossed from a (Pyrex) cup. The water breaks into falling drops, each of which leaves a trail of steam fog. The second picture is merely a detail of the first. In it one can more clearly see the fog trailing the individual drops.
