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28/10/2003
Forest fires stretching from the Mexican border to the suburbs of Los Angeles have destroyed thousands of homes and killed at least 17 people.
The fires, two of which are thought to have been deliberately started, are the worst southern California has seen in a decade. But what role has the weather played in their development and spread?
In southern California there is a large contrast between the wet and dry season. The wet season encourages abundant plant growth, and the subsequent dry season takes the moisture out of the plants. This makes it easier for wildfires to begin in the first place.
The reason for the abrupt change from wet to dry, and the California firefighters' nemesis, is the Santa Ana wind. In the late summer months, this strong wind blows from the Californian desert towards the sea changing the temperate coastal climate to a hot, dry and arid one.
The Santa Ana wind is not only fierce, it is very dry, dusty and hot. It occurs when a high pressure system forms over the Pacific northwest and a low pressure forms over Mexico. The resultant north-south pressure gradient causes strong winds that spill over the Sierra Nevada mountains from the northeast.
Just like the Chinook wind that sometimes affect Colorado's east slope, the air descends from the mountains and compresses, becoming warmer and drier. Since it originated in the Nevada desert the air was already pretty dry, so the warming process results in a wind so dry that it can desiccate vegetation and dry the soil. This often results in high fire dangers and resultant fires, just like we have seen this week in southern California.
Yesterday the Santa Ana wind began to ease in some areas, raising hopes that the firefighters could make some progress as things cool down.
Plenty of lore surrounds the Santa Ana. It is said to fuel aggression, and the Los Angeles Police Department often reports an upsurge in violent acts such as road rage and domestic abuse when the wind lingers too long. And it was during the hot, dry winds of 1984 that the noted serial killer Richard Rameriz, aka "The Night Stalker", went on a killing spree.
Related Links:
Weather Basics World Winds
Weather News from the last five days
27/10/2003
26/10/2003
25/10/2003
24/10/2003
23/10/2003
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