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.

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

The Palisades, Eaton, and Hurst fires covered more than 5,600 acres of Southern California as of Wednesday morning. Tens of thousands were under mandatory evacuation orders but the fires increased in size overnight, helped by the blustery Santa Ana winds.

At least five wildfires are ravaging Southern California, and the three largest — which are at 0% containment — have already killed at least two people, burned thousands of acres and prompted the evacuation of about 70,000 residents. Santa Ana winds coupled with dry conditions have created the perfect storm for the fires to spread.

The high winds have fanned flames, causing wildfires to quickly explode in size, and at times made it hard for air support to aid fire crews on the ground.