Can fog form in temperatures below 32 degrees?

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Dear Tom,
Water freezes at 32 degrees, so how is it possible to have fog (so-called “freezing fog”) below 32 degrees? Since the temperature is below 32 degrees, shouldn’t the fog droplets turn into snow flakes instead of remaining liquid until they freeze on contact with objects?
Mickey Conner, Beecher, ill.

Dear Mickey,
Freezing fog is actually regular fog that is occurring at sub-freezing temperatures (but at and below about 14 degrees, the liquid fog droplets do indeed freeze and become “ice fog”).

Fog droplets persist in liquid form at sub-freezing temperatures (down to 14 degrees) due to the surface tension of water molecules in the droplets. Surface tension becomes fairly strong as droplet size shrinks down to the tiny diameter of fog droplets (about 0.0004 inch) — so strong that it prevents the droplets from freezing.

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