Los Angeles county workers load sandbags in Pasadena. (AFP: Mario Tama/Getty Images)
In short:
Los Angeleslocals are preparing for a "high risk"' of flooding and landslides following the deadly fires that ripped through the countylast month.
The bulk of the county is under flash flood watch with areas affected by the scars of the blaze — which killed at least 29 people — at greater risk.
What's next?
The National Weather Service has warned people may have to leave their homes because of landslides.
Los Angeleslocals are preparing for a "high risk" of flooding and landslides following the deadly fires that ripped through the countylast month.
Forecasters said a huge rainstorm could see as much as 150 millimetres fall across parts of southern California on Thursday, local time.
The bulk of the county is under flash flooding watch with areas affected by the scars of the blaze — which killed at least 29 people — at greater risk of landslides.
Hillside areas such as Pacific Palisades, home to Hollywood stars including Tom Hanks and Jennifer Lopez, are at greater risk due to the soil being softer and drier after the fires.
The National Weather Service (NWS) said anyone living near such hillsides should be ready to leave their homes.
The afternoon and evening has been deemed the most dangerous time for flooding and landslides.
"There's a high risk for flooding, especially in and around the road areas and urban areas, as well as an appreciable risk for debris flows," NWS meteorologist Ryan Kittell said.
Workers in Los Angeles have gathered thousands of sandbags and concrete barriers in recent weeks to try to limit loose soil.
The incoming storm is being driven by an "atmospheric river," a giant corridor of rain that brings billions of litres of moisture from the Pacific Ocean.
While the immediate flood worries are sparking concerns, southern California badly needs the rain after near none in eight months.