Portugal Colonial - Fueling the Los Angeles fires: the Santa Ana winds

The windstorms occur when cold air gathers in the neighboring states of Nevada and Utah. As it moves west and then rushes down California's mountains, it heats up -- and dries out.

- Creating fuel, spreading fires -

The Santa Anas can both create the conditions for deadly wildfires and fuel them once they are underway -- drying out vegetation when they blow through, and then fanning blazes once they spark.

As the 23,700-acre (9,500-hectare) Palisades Fire and 14,000-acre Eaton Fire have raged around Los Angeles, fast-moving winds have exacerbated the situation, throwing hot embers into new patches of dried brush.

While firefighters sought to take advantage of a brief lull on Friday and Saturday, heavy winds were back with gusts up to 70 miles per hour (110 kilometers per hour) by Sunday, with harsh conditions forecast to continue this week.

- Cold air, hot winds -

Santa Ana winds usually occur between September and May, typically for a few days at a time.

When a high-pressure system forms over the deserts to California's east, it pushes air toward the Pacific coast.

As they move down the Santa Ana and Sierra Nevada mountains and shoot through valleys, the winds compress -- creating a rise in their temperature and a drop in their relative humidity.

With hot, dry gusts that can knock down trees or kick up dust and particulate matter, the winds have long caused problems in southern California.

The 2017 Thomas Fire, which destroyed more than 1,000 structures, was fueled in part by back-to-back Santa Ana winds.

- Frayed nerves -

The Washington Post likened the weather pattern to "a giant hair dryer," and writers have long noted the effect the winds seem to have on residents psychologically.

American author Raymond Chandler once described them as so hot they "curl your hair and make your nerves jump and your skin itch."

For Joan Didion, they blew "sandstorms out along Route 66, drying the hills and nerves to flash point."

R.Veloso--PC