Today I learned that the marine layer common on the California coast is due to the unusually cold water temperature relative to the air.

The big temperature difference between air and water causes cold air to get trapped at ground level. Because ocean evaporation is trapped in the cool air and colder air cannot hold as much water, water droplets form. So essentially a cloud forms on top of the water.

That’s also why the fog can disappear so quickly away from the coast. Being further from the water can cause a difference in temperature or humidity, stopping condensation.

The marine layer has been so thick this week. Now it makes so much more sense.