California: autumn heatwave sparks fears of new wildfires

California’s siege of wildfires has significantly quieted but forecasters warned on Tuesday that a fall heatwave could bring back critical fire weather conditions this week.

Fire weather watches will go into effect in much of northern California early on Wednesday due to high pressure producing hot and dry conditions with gusty offshore winds, the National Weather Service said. Peak gusts are likely to start late on Wednesday, with parts of California expected to see winds of up to 50 miles per hour.

“Critical fire weather conditions” are possible across the higher elevations of the North and East Bay as well as the Santa Cruz Mountains due to high winds, a dry air mass moving in from the north and a drop in relative humidity values, said the National Weather Service in San Francisco.

The utility Pacific Gas & Electric said it was likely some circuits would be turned off to try to prevent damaged power lines from starting fires. The utility, found at fault in two of the deadliest wildfires in California’s recent history, estimated that it may need to preventively shut off power to 50,000 customers in 21 of the state’s 56 counties – up to 149,000 Californians.

The National Weather Service in Los Angeles warned of “briefly critical fire weather conditions” in Los Angeles and Ventura counties starting on Thursday night, due to “weak Santa Ana winds” that “will likely worsen on Friday” in addition to “very warm to hot and dry conditions”. Southern California, which started the week with triple-digit high temperatures, is predicted to see particularly gusty north-east winds on Friday. Temperatures are expected to stay in the high 90s and lower 100s through the end of the week, with heat advisories in effect for many areas.

This week’s heatwave comes after a summer of record temperatures and a freak weather event in August that kicked off a historic fire season. More than 8,400 wildfires have burned well over 6,250 sq miles (16,187 sq km) in California since the start of the year. Many of them them ignited during a mid-August lightning siege of nearly 14,000 strikes. Thirty-one people have died and more than 9,200 structures have been destroyed.

Most of the huge fires have been fully or substantially contained over the past eight weeks but thousands of firefighters remain on the lines. While smoky conditions have cleared up in most regions, an unhealthy haze still hangs overhead in some areas.

Numerous studies have linked bigger US wildfires to climate breakdown from the burning of coal, oil and gas. Scientists say the climate crisis has made California much drier, making trees and other plants more flammable.