Two more people have died in a fast-moving wildfire that has torn through more than 56,000 acres of dry timber, grass and brush in Northern California since Friday, bringing the total of those killed in the blaze to four.
The blaze, named the McKinney fire, began in the Klamath National Forest in Siskiyou County, Calif., about 14 miles south of the Oregon state line, the authorities said, and has since grown to become the state’s largest wildfire this year.
It exploded in size over the weekend, prompting evacuation orders for thousands of people in nearby rural communities and leading Gov. Gavin Newsom of California to declare a state of emergency for Siskiyou County.
Lower temperatures and an increase in humidity, including some rain on Monday, enabled firefighters to build containment lines with hand crews and bulldozers, authorities said. The combination of moisture, thunderstorms and the resulting high wind speeds, however, were creating “an unstable atmosphere which may make firefighting conditions much more hazardous,” they said in a report on the fire’s progress on Tuesday.
Conditions had begun to shift on Tuesday afternoon, revealing clear skies over the fire and prompting a red flag warning, Mike Lindbery, a spokesman with the United States Forest Service, said by phone.
“We’ve had a couple of days to get in there and do some pretty good work, but we’re keeping an eye on the conditions today because they may force us off the hill.”
Mr. Lindbery said that the region where the fire was burning was not only “very combustible” but also extremely difficult to access. “Getting out of those areas can be very difficult; getting firefighters into that area can be very difficult,” he said.
Brian Nieuwenhuis, a meteorologist with the National Weather Service in Medford, Ore., said there was also a risk that too much rain could cause debris flow or mudslides, posing a danger to firefighters.
Though conditions had settled somewhat, he added, “fire activity should continue throughout the week.”
The fire, which remained zero-percent contained on Tuesday, is one of 60 large wildfires and fire complexes that have burned more than 1.6 million acres across the United States so far this year, according to the National Interagency Fire Center. In Siskiyou County, the China 2 and Alex fires, which are known together with surrounding lightning fires as the Yeti Complex, have burned more than 2,400 acres, authorities said.
The McKinney fire comes at a precarious moment for the state, which, along with the Pacific Northwest, faced abnormally high temperatures last week as a heat wave blanketed the region.
Days of scorching temperatures and drought conditions have contributed to the intensity of fires by making vegetation drier and more likely to ignite. Analyses have shown that human-caused climate change has increased the likelihood of such extreme heat waves.
Siskiyou County is in extreme drought, according to the U.S. Drought Monitor. Drought stress can kill trees, Mr. Nieuwenhuis, the meteorologist, said.
“You kill a tree,” he added, “and it just becomes a big piece of firewood.”