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Posts Tagged ‘Santa Ana fires’

On 2017 California wildfires were in the news. In the month of December powerful winds spread Southern California fires to destroy at least 175 structures and forced more than 27,000 evacuations. These high winds even have a name. Called the Santa Anas, the dry winds typically hit in late fall and are infamous in the Golden State.

California’s biggest and deadliest fires have been propelled by Santa Ana winds, which can gust to 100 mph (161 km/h). That wind speed makes smothering fires nearly impossible, said Chief Daniel Berlant, assistant deputy director the California Department of Forestry and Fire Protection, which is best known as Cal Fire. “In many cases, it’s all we can do just to try to control the path of the fire, trying to keep it away from people and homes,” Berlant said. “Stopping a fire when wind is 50, 60, 70 miles per hour is almost not possible.”

He added, “These fires burn into anything that’s in their path. A wind-driven fire is like a freight train, and stopping a freight train on a dime doesn’t happen.”

Helicopters can’t drop water or flame retardants in high winds, he said, because the gusts blow the liquids away.

Santa Anas also dry out trees, shrubs and grasses, turning them into tinder and spreading the blaze, he said.

“It’s the winds that spread the embers and fan the fire,” Berlant said. “That makes the fire burn fast and jump ahead, as embers fly in the high wind.”Santa Anas occur when high pressure over the Great Basin — a vast swath of Nevada, Utah and California — compresses air, cooking it, Cal Fire Captain Mike Mohler said.

That hot air then pushes southwest toward the coast.

“Our temperatures skyrocket,” Mohler said. “Humidity decreases down to single digits.”Climate change factors also play a role. What we see now is the same old story. ((Ack:By Anne C. Mulkern, E&E News/dec.6,2017)

Right now, on the outskirts of Redding, a rampaging wildfire is doing something that was once unusual: It’s burning fast…downhill.

“Fires are burning almost as fast downhill as they burn uphill,” said Cal Fire spokesman Scott McLean, from the scene of the Carr Fire, which by midday Friday had torched more than 44,000 acres and was only 3 percent contained.

That’s not typical. One of the first things wildland firefighters learn is that fires burn much faster uphill.

It’s simple physics: heat rises, so the heat from the fire warms and dries out the upslope fuels fastest. It’s also a case of proximity: if you draw a picture of a flame on a slope, you’ll see that there’s a much shorter distance between flame and ground on the uphill side than downhill, so the fire can jump directly from one blade of grass to another.Rapidly spreading downhill fires also played a major role in last winter’s Thomas Fire. It coincided with the longest Santa Ana wind event on record, according to Nauslar of the Wine Country fires. (Ack: Allie Weill, KQED science /PBS.org of July 28,2018)
compiled by Benny

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