California firefighters watch for ‘violent’ winds as nearly 30 blazes burn

Firefighters in northern California are warily watching for “violent” winds expected to return to the Napa-Sonoma area, amid continuing extreme heat and low humidity.

Red flag warnings of extreme fire danger were to continue into Friday evening for large swathes of northern California.

“It’s going to be a big firefight for us in the next 36 hours,” said Mark Brunton, Cal Fire operations section chief, during a late-morning briefing. He added commanders were forced to make do with “a limited amount of resources” due to competing demands for fire personnel throughout the state.

Related: 'There's a lot of hurt': four years of fire take toll on California's wine country

More than 2,000 firefighters are battling the Glass fire, which has charred 89 sq miles in Napa and Sonoma counties with almost no containment. It has destroyed about 250 buildings, including 143 homes.

The utility company Pacific Gas and Electric also cut power to another 3,100 customers in Napa county at the request of firefighters, the Santa Rosa Press Democrat reported.

Hot weather and the potential for fire damage could stress power supplies as people switch on their air conditioners. To avoid shortages, the California Independent System Operator, which runs the state’s power grid, issued a statewide Flex Alert for 3pm to 10pm Thursday. It urged customers to avoid using large appliances during that time and to keep the thermostat at 78F (25.6C) or above.

A mid-August heatwave strained the grid to the point where Cal ISO ordered utilities to implement brief rolling blackouts for the first time since 2001.

About 150 miles to the north of wine country, the Zogg fire, which also erupted during Sunday’s high winds and grew quickly, has killed four people, the Shasta county sheriff, Eric Magrini, said.

A man evacuated with severe burns on Sunday died at a hospital of his injuries on Tuesday, Magrini said. Three others died on Sunday.

The deadly blaze that spread to neighboring Tehama county has burned 86 sq miles and destroyed 146 buildings, about half of them homes. But fire crews made significant progress on Thursday, with officials saying the fire was now 26% contained.

The Glass and Zogg fires are among nearly 30 wildfires burning in California. Fire-related deaths in California this year total 30. Numerous studies in recent years have linked bigger wildfires in America to global warming from the burning of coal, oil and gas, especially because climate change has made California much drier. A drier California means plants are more flammable.

Firefighters say the intense blazes are also becoming harder to fight. On Wednesday, officials said wind-whipped flames led two firefighters to deploy the emergency fire shelters they carry in case of imminent danger from flames

The firefighters were assigned to the Glass fire on Sunday when gusty offshore winds fanned the fire, forcing them to deploy the shelters after flames overwhelmed them. The firefighters covered themselves on the ground with the space blanket-looking devices. They were not injured, the California department of forestry and fire protection said.

It’s the third time fire crews have had to deploy their fire shelters this month – a last-resort effort to save their lives that was once uncommon. On 8 September, 14 firefighters deployed emergency shelters as flames overtook them and destroyed the fire station they were defending in the Los Padres national forest. Three firefighters were hospitalized and later released. A day later, a crew fighting a deadly blaze in Butte county was overrun by flames when winds shifted; its members escaped with only minor injuries after deploying emergency shelters.

Meanwhile in Colorado and Wyoming, two big mountain wildfires were growing again after burning dozens of cabins and other structures.

A forecast calling for at least several more days of dry, breezy weather offered little help in the fight against the Cameron Peak fire west of Fort Collins, Colorado, or the Mullen fire west of Cheyenne, Wyoming.

Higher humidity, however, bought firefighters time before the fires’ usual afternoon flare-ups. They intentionally burned debris in some places to deprive the fires of fuel while helicopters dumped water on some of the hottest areas.

The fires are two of the Rocky Mountain region’s biggest fires in recent years. Each was burning through rugged pine forest dotted with communities of cabins, many of which aren’t inhabited year-round. Both were approaching 200 square miles in size.