Weather Watch:  Steam Fog

During late autumn and early winter when water temperatures are still
relatively warm but air temperatures are cold, <steam fog> can form
over relatively calm water.  Characterized by thin wisps of fog that
rise from the water surface like smoke, steam fog occurs overnight
during clearing skies and calm winds when the air temperature drops
below the surface water temperature.  If the fog is shallow and not
too thick, this is a great time to paddle because the water is flat
and the atmosphere is quite photogenic.

-David Schultz, NOAA/National Severe Storms Laboratory