In recent days, however, the region’s powerful Santa Ana winds—which have been fanning the flames—have begun to slow down. This lull has offered firefighters a reprieve and a key opportunity to make progress against the blazes, but forecasts suggest the Santa Ana will return next week. What are these gusts, and how have they become so strong?

Firefighters held the line against two massive wildfires that have ravaged parts of Los Angeles for the past week, even as desert winds and a parched landscape presented extremely hazardous conditions.