Officials battling the largest wildfire in California history say the rain forecast to arrive this week may complicate search and recovery efforts.
Firefighters say rains will aid efforts to contain the blaze but will also turn ash on the ground into a thick sludge.
Workers combing through homes and cars will struggle in the mud, and scorched landscapes may see land and mudslides, state wildfire officials warn.
Recent wildfires across the state have so far claimed a total of 80 lives.
The so-called Camp Fire in northern California has destroyed the town of Paradise, about 190 miles (290km) north of San Francisco, and left nearly 1,000 people unaccounted for.
The number of believed missing fell 283 late on Sunday, down from 1,276 people, they say, but gave no other details.
More than 10,500 homes have been destroyed due to the blaze, which officials said was 66% contained as of Monday but is unlikely to be fully contained before the end of the month.
Nearly 400 people searched for victims amid the scorched debris in Paradise on Sunday, wading through ash that officials say could turn into a thick paste, the Associated Press reported.
A breeze caused by Santa Anna winds may complicate fire-fighting efforts, forecasters warn.
But the rain may tamp down some of the smoke in the air that has caused health officials to release warnings due to poor air quality.
Melissa Schuster, a Paradise town council member, told ABC News on Monday that the "entire community of Paradise is a toxic wasteland right now".
Over the weekend, crews with cadaver dogs swept homes, vehicles, bathtubs, and mattresses among the rubble.
"We have been told we're to look as hard as we can, but it's still possible we may not be able to find something left of someone," Trish Moutard, a volunteer with the California Rescue Dog Association, told Reuters.
"If the fire stayed long enough and burned hot enough, the bones could, at a minimum, be fragmented down to such a small amount that we couldn't see them, and it's possible that even the dogs might not be able to detect them."
Sheriff Kory Honea said it was within the "realm of possibility" that the full death toll in Paradise may never be known.
He added that rescuers hope to complete their work before rains come mid-week, but may not be able to.
"As much as I wish that we could get through all of this before the rains come, I don't know if that's possible," the sheriff said.
Farther south, charred landscapes that were swept by the recent Woolsey Fire - especially those above roadways - are in danger of sliding due to heavy rains.
The coming weather is set to be the first major rainfall in about six months, and could bring dangerous conditions to the millions of acres that have been affected by multiple summer wildfires, such as the Mendocino Complex Fire which destroyed 75 homes in August and was declared the state's largest wildfire before it was overtaken this month by the Camp Fire.
"Threat of rockslides/mudslides, especially [Highway] 1 and canyon roadways in #WoolseyFire and #HillFire burn areas," the National Weather Service said in a tweet.
Officials say drivers should be cautious in the rain, which is already expected to cause traffic delays going into the Thanksgiving holiday.