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Santa Ana winds: How the West was hit by hurricane-speed winds

Santa Ana winds combined with a storm system to produce 100 m.p.h. winds in California and other Western states. The science behind the Santa Ana winds and this storm.

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The winds aren't even confined to California. In Las Vegas, winds are gusting at 29 mph (47 kph). At Mammoth Mountain's summit, the winds topped 150 mph, equivalent to a Category 3 hurricane on the Saffir-Simpson Hurricane Scale.

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The severe winds are even dangerous in Utah. Here, they are called simply "canyon winds," but the same phenomenon is at play. A high-pressure gradient east of the Rocky Mountains causes the winds to speed up going down the mountains. 

"By the time they hit the valley they're at an incredible speed," said Nanette Hosenfeld, a meteorologist with the NWS in Salt Lake City.

Wind gusts of up to 100 mph have been reported in Centerville, Utah. Interstate 15 has been completely shut down there because of flipped tractor-trailer trucks.

Wildfire hazard

The strong winds are a serious wildfire hazard in California. The NWS office in Los Angeles said there is "potential for high fire danger with rapid fire growth due to the strong offshore winds and low humidity values."

When the compressed winds are driven down mountain slopes they dry out and get hot.

"It can take a small fire and make it become a very large fire," said Julie Hutchinson, a battalion chief, with CalFire, the state's fire protection service. "If you get a fire started it can move very quickly."

In Southern California, the brush-covered hills are a big wildfire risk, Hutchinson said. Many areas of brush-covered hillsides have been sloughing off moisture in preparation for winter and are dangerously dry. Many areas are parched and battling a drought.

If a fire were to get out of hand, firefighters would not be able to use aircraft to fight the flames. Once the winds are above 35 mph (56 kph), firefighters must rely solely on boots on the ground, Hutchinson said.

Downed power lines are another big fire hazard. Los Angeles firefighters put out a 2-acre grass fire that burned overnight today at Occidental College sparked by downed power lines.

IN PICTURES: Santa Ana wind storm damage

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