Santa Ana winds occur when air flows west from a region of high pressure over the dry Great Basin to lower pressure off the California coast, According to Accuweather. As that cool interior air flows over and through mountain passes, it accelerates, sinks and compresses.

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.

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.