A webcam at Oat Mountain, northwest of Porter Ranch, suggested that the marine layer was 3,000 feet thick. What causes the marine layer? The air cools as it rises, which is important because colder air carries less water vapor than warm air. AdvertisementA strong inversion layer is necessary for the marine layer clouds to form, providing a lid that keeps them from rising off into the atmosphere. This layer of warmer air is the inversion layer, and it creates a cap limiting the vertical extent of the mixing near the surface.

Source: Los Angeles Times January 28, 2020 05:26 UTC