This wind fanned the deadly firestorms that turned swaths of Northern California wine country into an ashen moonscape. The name is informally applied to a hot, dry wind in the San Francisco Bay region that blows from the interior towards the coast. Known as an offshore wind — the direction the air is moving towards — it’s the reverse of the normal onshore flow of cool, moist air from the Pacific Ocean. The wind is spawned as high pressure builds over the West and air flows towards areas of lower pressure along the coast. The air is so dry that relative humidity levels plunge, drying out vegetation, making them ready to burn. The most infamous Diablo wind occurred in 1991. Remnants of a tiny blaze were whipped into an inferno in Oakland and Berkeley. The fire killed 25 people and destroyed more than 3000 homes.