I received a great question last week about my Clear Weather post regarding our foggy weekend in early January. A reader asked, “If fog is rain, why do San Diego and the Bay area have so much fog and so little rain?” Now is a good time to clarify and explain that there is more than one type of fog.

Last weekend was quite interesting as far as weather is concerned. We had near record warmth during the days and dense fog developed Friday afternoon and lingered through mid-morning on Saturday. We’re used to seeing fog in the mornings, but what causes it to form in the middle of the day?