Santa Ana winds in Southern California are often-fierce winds that topple power lines and trees and can turn a spark into a raging wildfire.

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 Santa Ana winds become particularly dangerous when combined with other climate conditions such as drought, which increases the risk of wildfires like the ones currently raging in the Los Angeles area.