The winds are common in California in the colder months, but they can sometimes help spread dangerous wildfires.

By the time the winds get to the point where the Eaton Fire broke out in Altadena on Jan. 7, it’s not uncommon for them to have less than 5 percent relative humidity, meaning essentially no moisture at all.

Devastating fires in the Los Angeles region are driven by Santa Ana winds blowing from California and Nevada’s interior deserts to the Pacific Ocean.