Lucas Fire explodes to 3,400 acres near Mendocino National Forest

A wind-driven wildfire burning along the border of Lake and Mendocino counties has exploded to more than 3,400 acres, forcing emergency evacuations and closing down a stretch of Highway 20.

The Lucas Fire, which broke out on Thursday morning near Potter Valley, more than tripled in size on Friday as high temperatures, dropping humidity and shifting winds drove the flames through dry grass and oak. Cal Fire reported on Friday afternoon that the blaze was just 5% contained.

Nearly 1,000 firefighters are on the ground, but the fire’s remote, rugged location has made it difficult to tackle. In many places, there are simply no roads.

"If there’s no roads, we make roads," said Tyree Zander, a spokesperson for Cal Fire’s Sonoma-Lake-Napa unit, which took full command of the firefight on Friday morning. Where bulldozers cannot go, crews are having to hike in on foot.

Thick smoke has also hampered efforts to attack the fire from the air, making helicopter and tanker drops difficult.

Local sheriffs have ordered evacuations for thousands of residents across a swathe of Lake and Mendocino counties. In Lake County, emergency orders are active for several zones, including areas around Bachelor Valley where structures are under immediate threat. A temporary evacuation centre has been opened at the Lake County Fairgrounds in Lakeport, which is also accepting displaced livestock and pets.

The fire has also closed Highway 20 at Bachelor Valley Road, Witter Springs Road and Saratoga Springs Road. Further north, the US Forest Service has issued an emergency closure for part of the Upper Lake Ranger District in the Mendocino National Forest, shutting down several campgrounds, including Middle Creek, Penny Pines and Deer Valley.

The cause of the fire is still being investigated, though Cal Fire confirmed that lightning strikes were recorded in the area shortly before the fire was first reported at 9:00 am on Thursday.

The fire initially looked manageable, starting at just 10 acres, but it jumped early containment lines when wind gusts reached 15 mph on Thursday afternoon. By Friday afternoon, temperatures in the area had reached 89 degrees Fahrenheit (31.7°C) with relative humidity dropping to 18%.

Conditions are expected to get worse before they get better. The National Weather Service has issued a fire weather watch for Lake County from Saturday morning through to Saturday night, warning of stronger winds and even lower humidity.

"We’re asking people to be fire safe," Zander said, urging residents to avoid any outdoor activities that could throw off a spark, such as mowing lawns or towing with loose safety chains. "We have a lot of resources assigned to this incident, and we don’t want to take people away for a new incident because of a newly sparked fire."

Elsewhere in the region, firefighters are having more success. The 51-acre Steele Fire, which ignited on Wednesday near Lake Berryessa in Napa County, is now 68% contained.