Thanksgiving dinner was in the works, and I had opened the lid of the roaster to evaluate the progress of the turkey. Sophia Claire wondered aloud why the steam "looks like an atom bomb explosion" with a mushroom-shaped cloud above. After several observations of the rising steam, she noticed that -- and wondered why -- there was a large puff of steam on top, with a straight streaming tail beneath. First she hypothesized that the steam was puffing out when it hit the ceiling -- but then she recognized that the steam puffs out as soon as it exits the container (a turkey roaster), long before encountering the ceiling, and that the following bits of steam move straight with neither puffs nor curls.
And then she hit on it -- she remarked that it must be that the hot steam is hitting against the cold air in the room surrounding the container, with the result that the steam looks as though it has bumped into something -- cold air -- thus causing steam puffs and swirls. And, she explained, after the cold air is pushed out of the way, then the rest of the rising steam moves in a relatively straight path.
(Many clouds and streams of steam contributed to this conclusion. Little wonder that our turkey was a little dry-ish...)