Driven by Santa Ana winds, several large wildfires flared across Southern California over the weekend of October 20, 2007. This image of the area around Los Angeles captured by the MODIS on the Aqua satellite on October 21, shows smoke pouring from several large blazes northwest of Los Angeles at approximately 2:50 pm local time. Although Aqua MODIS only caught the edge of the scene during this satellite overpass, the plumes of smoke and dust that can be seen blowing off the coast in the large image indicate the intensity of the winds and the presence of additional fires farther south.
The blaze intensified in a quick amount of time. When Aqua passed over in the morning, around 11:35 AM, the fires had just small plumes of smoke. You can see the morning image on Earth Observatory.
Santa Ana winds are a California firefighter’s nightmare. These blustery, dry, and often hot winds blow out of the desert and race through canyons and passes in the mountains on their way toward the coast. The air is hot not because it is bringing heat from the desert, but because it is flowing downslope from higher elevations. As fall progresses, cold air begins to sink into the Great Basin deserts to the east of California. As the air piles up at the surface, high pressure builds, and the air begins to flow downslope toward the coast. When winds blow downslope, the air gets compressed, which causes it to warm and dry out. In fact, the air can warm at a rate of 10 degrees Celsius per kilometer of descent (29 degrees Fahrenheit per mile). Canyons and passes funnel the winds, which increases their speed. Not only do the winds spread the fire, but they also dry out vegetation, making it even more flammable.