Meteorologist Dan Satterfield explains this occurrence on his blog:
Cool air offshore was very nearly at the saturation point, with a temperature near 20ºC and a dew point of about 19.5ºC. The air at this temperature can only hold a certain amount of water vapor, and how much it can hold depends heavily on the temperature. If you add more water into the air, a cloud will form, but you can also get a cloud to form by cooling the air. Drop the temperature, and it can no long hold as much water vapor, so some of it will condense out and a cloud will form.
