The devastating fires that have killed at least five people and forced the evacuations of tens of thousands of residents across the Los Angeles region are driven by Santa Ana winds that blow from the deserts of interior California and Nevada out to the Pacific Ocean.

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

Santa Ana winds are caused by strong high pressure over the Great Basin region of the West creating a pressure gradient that amps up winds through the mountains, foothills and sometimes valleys of Southern California. In this case, the winds are getting a major boost from a strong upper-level low pushing southward across the state.

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.

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.