El Niño 2015-2016: El Niño and Southern California Weather
Shifting the jet stream and enhancing storms are the mechanisms for bringing flooding rains to Southern California. Storms ride the jet stream, which steers them into North America. During our rainy season, the jet stream will normally rope its way down into the Pacific Northwest carrying storms from the Gulf of Alaska. Occasionally this current of air will move storms into California, with Southern California getting the tail end of these systems.
The El Niño tends to cause the jet stream to make broad southerly dips, compared with its normal track. Sometimes the jet is energized by El Niño and splits, taking a southerly dip into the subtropical regions near Hawaii. This is called the Pineapple Connection and it can bring destructive rains to Southern California. First, the storm track comes over the Southland more often. Second, the Pineapple Connection functions like a conveyor belt drawing tons of moisture over California.
El Niño can also produce other dangerous weather. Strong tornadoes typically do not develop in California, although they can occur anywhere on the planet. However, intensified thunderstorm activity can spawn tornadoes. The El Niño of 1982/83 gave Southern Californians a taste of these vicious storms. In November, the largest outbreak of tornadoes ever in California happened in a single day. Most of these were minor twisters. However, a few months later in March, a more destructive tornado ripped off portions of the L.A. Convention Center roof and caused widespread property damage in South L.A.