A winter storm moved into Southern California on Sunday afternoon, bringing scattered showers and warnings of more significant rainfall and possible flooding in some areas in the evening.

The rain was already causing traffic tie ups on roads and freeways throughout the region, officials said. Forecasters warned of flooding in parts of downtown Los Angeles, Pasadena, Alhambra, the South Bay and elsewhere.

Scott Sukup, a meteorologist in the National Weather Service’s Oxnard office, said an average of 0.5 to 1.0 inches of rain is expected to fall throughout the Los Angeles basin, with heavier rain possible in the mountains.

The “main part of the storm” is expected to begin around 6 p.m. Sunday, Sukup said. It will continue until around 4 a.m. Monday.

“The bulk of the rain should be done before rush-hour,” Sukup said.

Forecasters also expect 3 to 8 inches of snow in the San Gabriel Mountains above 7,000 feet.

Where the heaviest rain falls will depend largely on where thunderstorms occur, which Sukup said is hard to predict. The Weather Service has issued a flash-flood watch for burn areas where heavy rain could result in debris flows.

The agency also issued a flood advisory Sunday afternoon, warning that the scattered showers that have already hit could cause flooding in areas throughout the region.

The storm has the potential to be the largest in the L.A. area this fall. So far, the basin has only gotten about 0.5 inches. If Sunday’s storm does end up dumping an inch of rain on the region, that would “put us above normal for the season,” Sukup said.

As the storm moves through the area, residents should expect overnight low temperatures in the 50s, Sukup said.

Northern California is also being hit by rain this week, which is producing more much-needed snow in the parts of the Sierra Nevada mountains, a key source of water for California as the state deals with a fifth year of drought.

https://twitter.com/NWSLosAngeles/status/800447703599681538

https://twitter.com/ABC7/status/800447589883768832

MORE LOCAL NEWS

L.A. prepares to help undocumented immigrants during a Trump presidency

Could Donald Trump's education policy change schools in California and nationwide?

Los Angeles feels the pension squeeze

UPDATES:

2:30 p.m.: This story was updated with new information from a National Weather Service meteorologist.

1:10 p.m.: This article was updated with new details about the storm.

This story was originally published at 7:40 a.m.