LOS ANGELES, Dec. 22 (Xinhua) -- After a powerful series of storms battered Northern California, forecasters warned Monday that an "atmospheric river" system is intensifying and moving southward with expected winds and heavy rain.

Raging floodwaters claimed the life of a motorist in Redding, a city in the northern part of the U.S. state of California, on Sunday. The driver was found dead in a submerged vehicle, according to Redding Mayor Mike Littau.

Driving the deluge is the potent "atmospheric river" -- a vast corridor of concentrated moisture moving from the tropics. As the system pivots toward Southern California, the risk of urban flooding grows.

Forecasters indicated that downtown Los Angeles had an 80 percent chance of 2 inches (about 51 millimeters) or more of rain from Tuesday through Christmas Day, with 4 to 8 inches expected from Tuesday through Saturday across much of Los Angeles County.

Officials on Monday continued to urge caution, advising travelers to prepare backup plans as the state braces for a wet and hazardous holiday week. ■