An atmospheric river of moisture, stretching over 3,000 miles past Hawaii, was streaming into California on Wednesday.

Forecasters have warned California residents that unsettled weather through Thursday is likely to bring heavy rains, strong winds and mountain snow as the storm moves down along the West Coast. A similar storm will threaten the region early next week.

When the tail end of an atmospheric river stretches back toward Hawaii, like this one, it is often called a “Pineapple Express.”

The rainfall began during the Wednesday morning commute in some areas and continued during the afternoon farther south down the coast.

Flooding concerns, like overwhelmed storm drains that can lead to road closures, will be widespread, and the heavy rain that falls could create localized areas of flash flooding, with urban areas, roads, small streams and burn scars the most vulnerable, forecasters said.