The Pineapple Express is a Pacific Ocean subtropical jet stream that brings warm moist air from Hawaii (where pineapples are grown) to the U.S. West Coast states of California, Oregon, and Washington, as well as the Canadian province of British Columbia.Less dramatic, but nonetheless depressing for Angelenos is "June Gloom" or, as it's called in May, "May Gray." We are currently experiencing May Gray, which is characterized by the following:
The combination of moisture-laden air, atmospheric dynamics, and orographic enhancement resulting from the passage of this air over the mountain ranges of the West Coast causes some of the most torrential rains to occur in the region.
The early mornings are typically foggy. The fog turns to low clouds by late morning and early afternoon. Finally, by late afternoon, the clouds burn away and the sun shines. Often the overcast will burn off quickly inland, but it will stay cold and cloudy most of the day for the coastal areas of Southern California. Southern California residents are used to this yearly weather pattern, but it usually comes as a great disappointment to tourists to the area who expect the weather to be sunny year-round.From Wiki.