Southern California's seasonal "June gloom" weather, caused by a marine layer that traps smog over the Los Angeles basin, will probably pay an extended visit this year.

CNN: Western U.S. to get smoggy summer, fall

The cold waters mean a large temperature contrast between the land and ocean -- conditions that favor the formation of a strong inversion layer that traps smog over cities, such as the Los Angeles, Calif.

CNN: Western U.S. to get smoggy summer, fall