Waves of rain are expected over the next two days in California, with the heaviest hitting the southern part of the state.
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For Montecito, California, which endured deadly mudslides two months ago, this storm could bring more debris flow.
In Santa Barbara County, 30,000 people were told to evacuate, including residents of Montecito.
The Jan. 9 storm in Montecito killed 21 people, left two children missing and destroyed many homes.
Dave Zaniboni of the Santa Barbara County Fire Department described the aftermath of the January mudslide as a "battlefield" and "unrecognizable."
"I've been doing this for 32 years and I've never seen anything just so tragic in my life," he told ABC News Wednesday.
Zaniboni said he recovered a 6-year-old boy who died in the Jan. 9 storm, and he's since stayed so close to that boy's family that he feels an immense attachment to them.
"As much as I feel like I've been able to sort of help them through some tragic times," he said. "They were really able to help me so much, too. They just gave me a purpose during all of this... It changed me."
Zaniboni said the "monster storm" on Jan. 9 "dropped a half an inch of rain in 15 minutes and an inch of rain in half an hour, and that's what caused the debris flow."
Now, the area is expecting a bigger storm, but it will be over a longer period of time, which eases the debris flow, said Zaniboni.
"This is the biggest storm we've had since Jan. 9," Zaniboni added.
The heaviest rain is expected to reach Southern California on Thursday, and rainfall rates could be as high as 1 inch per hour -- causing possible mudslides and rock slides.
On the WEST COAST....moisture is seen streaming in from the Pacific Ocean - here's a view from your #GOESEast satellite this morning. Several inches of rain are expected, which will likely lead to debris flows and flooding! https://t.co/VyWINDk3xP ???????? pic.twitter.com/lkXzEk7pFr— NWS (@NWS) March 21, 2018
Rainfall totals in Los Angeles and Santa Barbara could reach 2 to 3 inches. The coastal range could see as much as 5 to 10 inches.
"Because this storm is so widespread and so long in duration, we're concerned about any heavy cells, any thunderstorm that might center over these mountain areas," Zaniboni said. "Right now they're doing a great job as far as the creeks and stuff go, they're funneling all the water off the mountains and the creeks are running clear."
"But after Jan. 9 all of those creeks... were jam-packed, clogged up with debris and trees and boulders and houses," Zaniboni said. "Since Jan. 9 the Army Corps of Engineers has been in here working hand-in-hand with Santa Barbara County Flood Control, they've been working around the clock and got all of those debris basins and all those creeks clear."
As Santa Barbara braces for the rain, the Sierra Nevada Mountain range in Northern California is preparing for snow, the area could see close to 5 feet of snow by Saturday.
ABC News' Kayna Whitworth and Scott Shulman contributed to this report.