Firefighters Battle California Wildfire as Heat Wave Fades, Santa Ana Winds Loom

(Bloomberg) -- A fast-growing wildfire forcing evacuations in Southern California shows the danger the state now faces, as record-smashing heat waves dry out the landscape just as the Santa Ana wind season is due to begin.

The Line Fire east of Los Angeles had burned more than 21,000 acres as of midday Monday, scorching an area where residential neighborhoods and commercial buildings border the San Bernardino National Forest. Just 3% of the fire is contained, according to the California Department of Forestry and Fire Protection, or Cal Fire. The San Bernardino County Sheriff’s Department has ordered thousands of people to evacuate, and more than 36,000 structures are threatened. 

The last two winters were unusually wet across California, leading to explosive growth of wildflowers, grasses and brush. That vegetation has now been parched by the state’s annual dry season and a series of heat waves, creating fuel for fires. Forecasters reported record daily high temperatures Sunday in seven Southern California cities, from coastal Los Angeles and Long Beach to the inland hub of Riverside, which reached 110F (43C). 

While the latest blast of heat is expected to break early this week, it has left the region primed for fire when offshore winds arrive. 

Whether they are called Santa Anas, Sundowners or Diablos, the winds tend to rise in autumn, as high pressure builds over the US Great Basin and pushes air toward the coast. The gusts become warmer and drier as they roll downhill toward the Pacific, threatening to turn any fire – whether caused by humans or a lightning strike – into a blowtorch. 

Forecasters are unable to predict exactly when the winds will arrive from year to year, but it’s clear that this upcoming Santa Ana season could be perilous for a broad swath of the state. “The pre-conditions are going to be favorable for extreme Santa Ana wind-driven fires,” said Daniel Swain, a climate scientist with the University of California Los Angeles.

--With assistance from Brian K. Sullivan.

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