The 14,000-acre fire currently five percent contained and it's getting close to merging with the even larger Rocky Fire.
Cal Fire says the fire appears to be gaining ground and heading north away from populated areas. The fire is burning through extremely dry and steep terrain.
"It's not about extreme temperatures. It's not about gusty winds. It's really about the dry conditions," said a Cal Fire spokesperson.
PHOTOS: Smoke visible from Jerusalem Fire in Lake County
Mandatory evacuations have been issued, though not everyone is leaving. Robert and Deborah Lipari nervously watched the fire burn Tuesday on the hill opposite their olive farm, Villa Barone.
"It's hour to hour. Come outside every hour and take a survey," Robert Lipari said.
The couple lives inside the mandatory evacuation zone, but they are choosing to stay put.
"They know we are here and they know we have an escape route," said Deborah Lipari.
"We're called refusers because we won't leave. We're staying," Robert Lipari said.
Firefighters say they can't force people to leave, but only warn them of the danger.
More than 1,000 firefighters are on the front lines, some who fought the Rocky Fire just days ago. Winds appear to be moving the fire to the north.
"That would be more advantageous than if it came west, because if it comes west then you have Hidden Valley and a lot of residents," said Cal Fire spokesman Hugo Patino.
Terry Atkins has most of his belongings in the back of his pickup truck. His dogs are also with him. This is the second time he has left his home in two weeks.
"The only reason we had to really evacuate was because of the dust and the smoke and we were starting to feel a little funky," Atkins said.
Cal Fire is putting out the call for more firefighters. The cause of the fire is still under investigation.
Meanwhile, firefighters have nearly surrounded the larger nearby blaze that started about two weeks ago and has burned 109 square miles. The Rocky Fire destroyed 43 homes, but all evacuations have been lifted.
MANDATORY EVACUATIONS AND ROAD CLOSURES
Mandatory Evacuations are in place for the Jerusalem Valley area east of Spruce Grove. This includes Tinilyn Road, Nicholas Way, Jaclyn Road, June Bug Drive, Jerusalem Grade, Jerusalem Valley Road, Jerusalem Road, W Jerusalem Road, Canyon Road, Coon Flat Road and Daly Place. Advisory Evacuations are issued for Grange Road from Luchetti Ranch Road east to Bucksnort Creek, Butts Canyon Road from Bucksnort Creek east to the Napa County Line, Morgan Valley Road from the Reiff Road intersection east to the Napa County Line and Reiff Road from the Morgan Valley Road intersection east to the Yolo County Line.
Jerusalem Valley Road is closed to all traffic at Spruce Grove Road, Morgan Valley Road from Reiff Road southeast to Napa County Line, Reiff Road from Morgan Valley east to Yolo County Line and Berryessa Knoxville Road closed from Lake Berryessa north (per Napa County Sheriff).
The Lake County Office of Emergency Services says an evacuation center for both wildfires is available at Middletown High School at 20932 Big Canyon Road, and a temporary shelter for pets and animals has opened at 6885 Old Highway 53 in Clearlake.
Grange Road from Luchetti Ranch Road east to Bucksnort Creek; Butts Canyon Road from Bucksnort Creek east to the Napa County line; Morgan Valley Road from the Reiff Road intersection east to the Napa County line; Reiff Road from the Morgan Valley Road intersection east to the Yolo County line.