Air sinking compresses and warms at this rate. Advection Fog -The water off the coast of California is so cold, because of upwelling adjacent to the coast due to the California current. This works up to an elevation of 4,000 feet. Similiar as when air moves over warm mountains. Despite cooling, there are no clouds or rainfall in the Central Valley.
Fog is a cloud that has formed on the ground.
This happens when air at the surface is cooled to its dew point. In the case of California's coastal fog , air over the ocean cools to its dew point and the resulting fog is blown typically toward the coast by persistent north or northwest winds. If we look at a map of typical summer sea surface temperatures off the California coast, we see that water temps just off shore run in the 50s, while farther to the west they climb into the 70s. Air to the west moving over the immediate coastal waters is thus cooled significantly, resulting in fog. The western coasts of all continents have similar cold currents just offshore, although in the southern hemisphere they flow rom the south rather than north.