Tens of thousands of people have fled their homes as a brush fire in the Pacific Palisades has grown to nearly 20,000 acres on Thursday.

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.

The blaze began shortly after the start of a Santa Ana windstorm that the National Weather service warned could be the strongest to hit Southern California in more than a decade.