LOS ANGELES (AP) — A strong Pacific storm heading toward California will likely bring an extended period of rain and the threat of flooding and debris flows in areas near wildfire burn scars, forecasters said Monday.

The system, known as an atmospheric river, was tapping into a deep plume of subtropical moisture that could bring the highest rainfall totals of the season for southwestern parts of the state, the National Weather Service said.

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“Tuesday will start off uneventfully…. But then there will be a startling change in the weather,” the Los Angeles-area weather office said.

Preliminary rainfall estimates through Thursday night or early Friday range from 2-4 inches (5-10 centimeters) across coastal and valley areas and 4-6 inches (10-15 centimeters) on south- and southwest-facing foothills and mountains, forecasters said, adding that local amounts up to 8 inches (20 centimeters) can’t be ruled out.

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Where exactly the peak rainfall will occur was still uncertain, but meteorologists said it seemed likely it would be Santa Barbara County.

A stretch of the county’s south coast was hit hard by a storm on Jan. 9, unleashing massive debris flows from scorched mountains above the community of Montecito. Hundreds of homes were damaged or destroyed, 21 people were killed and two still remain missing.

On Saturday, the county’s emergency managers issued a “pre-evacuation advisory” for at-risk areas below four wildfire scars. The advisory is intended to give residents 72 hours to prepare for evacuation.

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The storm was also expected to spread rain up the coast through the San Francisco Bay region and eastward to the Sierra Nevada, where a flash flood watch will go into effect Wednesday from about Yosemite southward.