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The Santa Ana winds (also known as Santana winds) are strong, extremely dry offshore winds that characteristically sweep through in Southern California and northern Baja California in late fall into winter. They can range from hot to cold, depending on the prevailing temperatures in the source regions, the Great Basin and upper Mojave Desert. However, the winds are remembered most for the hot dry weather that they bring in the fall.

Santa Ana's are a type of drainage wind, an offshore wind that results from the buildup of air pressure in the high-altitude Great Basin between the Sierra Nevada and the Rocky Mountains. When upper level winds are favorable, this high altitude air mass spills out of the Great Basin and is propelled gravitationally towards the southern California coastline, generally as a northeasterly wind.

It is often said that the air is heated and dried as it passes through the Mojave and Sonoran deserts, but according to meteorologists this is a popular misconception. The Santa Ana winds usually form during autumn and early spring when the surface air in the elevated regions of the Great Basin and Mojave Desert becomes cool or even cold, although they may form at virtually any time of year. The air heats up due to adiabatic heating during its descent, which means that the air rubs against the atmosphere and warms up.

While the air has already been dried by orographic lift before reaching the Great Basin as well as by subsidence from the upper atmosphere, the relative humidity of the air is further decreased as it descends from the high desert toward the coast, often falling below 10 percent.

The air from the high desert is initially relatively dense owing to its coolness and aridity, and thus tends to channel down the valleys and canyons in gusts which can attain hurricane force at times. As it descends, the air not only becomes drier, but also warms adiabatically by compression. The southern California coastal region gets some of its hottest weather of the year during autumn while Santa Ana winds are blowing. During Santa Ana conditions it is typically hotter along the coast than in the deserts

In the Los Angeles Basin, the winds are often credited with the extremely high visibility experienced in the area during the winter, in contrast to the hazy, smoggy summers.

The adverse pulmonary health impacts have been understood by local doctors for decades; the winds pick up and transmit grit, dust, pollens, mold spores and other irritants and allergens for considerable distances.

Residents regularly notice a build-up of dust in their homes and grit on their properties during these periods, which are frequent during the winter.

Gary Hall, the ghostpainter