Here’s a classic example of coastal fog in central/northern California.

From this MODIS near real-time satellite image, you can see the stratus clouds (aka, fog) being pushed down the coast from the northwest to the southeast. The afternoon weather is great if you live in a south-facing area like parts of Marin county and or Santa Cruz, but not so good for north- or west-facing areas such as the western parts of San Francisco… unless you really like fog that is.

I don’t know the exact time this photo was taken, but it was probably in the afternoon, since most of the coast was foggy yesterday morning with clearing on parts of the coast in the afternoon.