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San Diego County has been stuck in the midst of one of its driest periods in recorded history. Since July 2006, the region has received little more than 4 inches of rain.

While that has created fire-prone conditions throughout the region, nothing is playing a more catastrophic role in pushing the fires than Santa Ana winds that are screaming through the mountains east of San Diego. Gusts are blowing above 60 mph, fanning the flames.

“There’s multiple variables on all of these fires,” said Rick Halsey, a fire ecologist and director of the California Chaparral Institute. “But the No. 1 driver is the Santa Ana wind conditions.”

Santa Anas occur when high pressure moves in over Nevada’s Great Basin. Low pressure along the coast serves as a giant vacuum. Cold air drops out of the desert and compresses as it decreases in elevation.

As it drops, the air heats up and dries out. It can warm as much as 29 degrees Fahrenheit for each mile it descends.

“It funnels down canyons like a bat out of hell,” Halsey said. “It’s like a drain being pulled and all of this air comes screaming down any corridor it can find.”

ROB DAVIS

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