Marine Layer

A marine layer is a dense mass of cool, moist air which accumulates over the surface of large bodies of water, especially oceans. It is caused by a temperature inversion, meaning that the air close to the ground is colder, rather than warmer, while warm air above the marine layer presses down on it, preventing it from dissipating. Marine layers are responsible for the fog which plagues many coastal communities, particularly along the US West Coast, and can persist for several days or weeks. The persistent marine layer is often referred to as "June Gloom" in Southern California.