The "largest storm of the season" has made its way to Southern California bringing heavy rainfall and prompting evacuation warnings in burn scar areas across the region, weather officials say.

The National Weather Service said a "significant storm" will affect the entire day. Moderate to heavy rain will continue throughout the day and increase in the afternoon into the evening.

The heaviest rain is expected to fall Thursday night. The NWS said the rainfall totals are not a concern with the system, the main worry is the rainfall rates. Forecasters said there is a high risk for flooding and debris flows in burn scar areas.

A flash flood watch is in effect until Thursday evening for much of Los Angeles and Ventura counties.

"Heavy rain over the burn scars could trigger life-threatening and damaging flooding and debris flows," the NWS said.

LA and Ventura counties could receive 1.5 to 3 inches of rain by the end of the storm. The mountains and foothills could receive 3 to 6 inches of rain. Forecasters expected rainfall rates to be between .5 and 1 inches of rain during the peak of the storm.

"There is a higher probability of rainfall rates in excess of 1 inch per hour which would very likely cause substantial debris flows if they occurred over a recent burn area," the NWS said.

Gusty northwest winds are also expected to accompany the storm. A high wind warning will be in effect Thursday morning until 1 a.m. Friday for parts of Ventura County and the San Gabriel Mountains. Weather officials warn that damaging winds could cause downed powerlines and trees. Widespread power outages may occur.

The storm will weaken on Friday with scattered showers lingering in the morning.