The National Weather Service has warned about the threat of flash floods with rain predicted for areas in northern California affected by the state's deadliest wildfire,

Areas near the mountains, in particular, have no trees to stop rainwater due to the blaze, and the scorched earth will not be able to absorb even the moderate amount of rain expected.

The pending rain also brings the problem of mudslides and boulders on local roads as well as ash and debris being carried into streams.

“Cal Fire and weather service officials said the soil just below the surface gets packed by intense wildfire heat and can become impermeable to water, causing an almost instant wash off of debris, ash and loose dirt during extremely heavy rainstorms,” the Sacramento Bee reported.

Those in the vicinity of the Camp Fire in Butte County, the Delta and Hirtz fires near Shasta City and Redding, California, and residents near the Mendocino Complex fire around Clear Lake, have all been warned of the flash floods.

Most people in the area evacuated during the height of the blazes but returned to survey the damage.

Camp fire: Video shows 'firenado' raging during California wildfire

Several residents have been staying in caravans or tents in vacant parking lots as they try to recover possessions and rebuild their lives.

Due to the possible flooding though, more indoor shelters have been opened in the region.

Wildfires spread across California – in pictures Show all 32 1 /32 Wildfires spread across California – in pictures Wildfires spread across California – in pictures Firefighters battle a blaze at the Salvation Army Camp in Malibu Getty Wildfires spread across California – in pictures Flames from the Camp fire burn near a home atop a ridge near Big Bend AFP/Getty Wildfires spread across California – in pictures Cathy Fallon (centre) who stayed behind to tend to her horses during the Camp Fire, embraces Shawna De Long (left) and April Smith who brought supplies for the horses Reuters Wildfires spread across California – in pictures A helicopter drops flame retardant on a wildfire in Malibu Getty Wildfires spread across California – in pictures An air tanker drops water on the fire along the Ronald Reagan Freeway in Simi Valley AP Wildfires spread across California – in pictures An abandoned car from fleeing residents of Paradise in the Pentz road area EPA Wildfires spread across California – in pictures A firefighter tackles the fire along the Ronald Reagan Freeway in Simi Valley AP Wildfires spread across California – in pictures A Jack In The Box fast food restaurant burns as the Camp fire moves through Paradise, California AFP/Getty Wildfires spread across California – in pictures Yuba and Butte County Sheriff officers label a body bag AFP/Getty Wildfires spread across California – in pictures Firefighters hose down trees on Bell Canyon Road, near Malibu AFP/Getty Wildfires spread across California – in pictures A fire burns at the Salvation Army Camp Getty Wildfires spread across California – in pictures A firefighting DC-10 makes a fire retardant drop over a wildfire in the mountains near Malibu Canyon Road AP Wildfires spread across California – in pictures A house burns in Paradise, California AFP/Getty Wildfires spread across California – in pictures Bins have melted and ballooned in the heat in Magalia, Butte County EPA Wildfires spread across California – in pictures Satellite image taken on 8 November shows plumes of smoke from the Camp Fire stretching across portions of Northern California AFP/Getty Wildfires spread across California – in pictures Firefighters battle the Camp Fire AP Wildfires spread across California – in pictures Firefighters battle the Woolsey Fire Reuters Wildfires spread across California – in pictures Deputy Coroner Justin Sponhaltz, of the Mariposa County Sheriff's Office, recovers human remains found at a home destroyed by the Camp Fire AP Wildfires spread across California – in pictures Buildings burn in Paradise, California EPA Wildfires spread across California – in pictures Local residents bring their horses to Zuma Beach and away from the Woolsey Fire in Malibu Reuters Wildfires spread across California – in pictures A used car dealership burns in Paradise, California Reuters Wildfires spread across California – in pictures Yuba and Butte County Sheriff officers inspect a burned vehicle after discovering remains nearby in Concow AFP/Getty Wildfires spread across California – in pictures Firefighters battle the flames in Thousand Oaks Reuters Wildfires spread across California – in pictures A house burns in Paradise, California AFP/Getty Wildfires spread across California – in pictures A house burns in Paradise, California AP Wildfires spread across California – in pictures Search and rescue teams work to evacuate patients from the burning Feather River Hospital in Paradise, California AFP/Getty Wildfires spread across California – in pictures Embers blow in the wind in Paradise, California AFP/Getty Wildfires spread across California – in pictures In Butte County, the sky is filled with the smoke of the Camp Fire EPA Wildfires spread across California – in pictures Firefighters at work in Thousand Oaks Reuters Wildfires spread across California – in pictures A house burns in Paradise, California AP Wildfires spread across California – in pictures The burned remains of a house and car are left after the Camp Fire in Paradise, California AFP/Getty Wildfires spread across California – in pictures A shop burns in Paradise, California AFP/Getty

The storm is expected to begin midweek and last through part of the weekend, with another storm hitting next week.

Search and rescue crews may also be hampered by the rain.

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They are surveying a massive area. “Here we’re looking for very small parts and pieces, and so we have to be very diligent and systematic,” said Joe Moses, a commander with the Monterey County Sheriff’s Office told the local CBS News station.

Sheriff Kory Honea expressed doubt the searches would be completed before the rain began.

There is some positive news from the rain - firefighters and public health officials say it will help to control or stop the blazes and clear up the unhealthy amounts of smoke and debris that have been in the air for the past 10 days.