The first storm hit the San Francisco Bay Area on Wednesday and moved south on Thursday, arriving in Los Angeles just in time to snarl the morning commute.
The river of rain “will be taking aim at mostly Southern California” on Thursday, National Weather Service forecaster Bob Oravec said.
The heavy rain was forecast to create mainly localized areas of flash flooding, with urban areas, roads, small streams, and burn scars the most vulnerable, the weather service warned.
The storm – which some forecasters likened to "a giant firehose" – was expected to move south through California Thursday night before shifting inland over the Southwest from Friday to Saturday, AccuWeather said.
This storm is being referred to as a Pineapple Express, the most well-known nickname for an atmospheric river, which occurs when the source of the moisture is near Hawaii. When a Pineapple Express hits land in the western United States and Canada, it can cause heavy rain and snow. In California, it can cause several inches of rain in a day.