Fires

Fierce Rocky fire, 40 percent contained, was spurred by windy weather of its own making

The Rocky fire in Lake, Yolo and Colusa counties stands out as one of the most ferocious blazes burning in California so far this year – so fierce it’s creating its own weather.

On Thursday morning, the California Department of Forestry and Fire Protection said the fire was 40 percent contained. It had consumed 69,600 acres and destroyed 43 residences and 53 outbuildings. Fire officials said 13,118 people remain under evacuation orders.

“Computers have not been able to generate what we are seeing with this fire. It doubled in size in five hours and the computer said it would take seven days to do that. This is an extreme fire situation right now,” said Jason Shanley, Cal Fire spokesman.

To ignite, fires require three components: fuel, oxygen and heat, but once a fire has started, three factors determine how it spreads: the kinds of flammable materials – known as fuel – the weather and topography. In the case of the Rocky fire, all three of these elements are working against the firefighters.

Fuel

Drought conditions have played a role in making the Rocky fire particularly fierce. “This fuel has not had water in a long time, making it easier to burn,” Shanley said.

The fire is also heating up the surrounding vegetation, making it more flammable, which in turn feeds the flames.

While trees are burning, the Rocky fire is being fed largely by thick brush and other vegetation – a type of fuel that is particularly flammable. Twigs, sticks and smaller materials have large surface areas compared with their volumes, which means they heat up quickly to 572 degrees, the flashpoint of wood. Every material has a flashpoint – the specific temperature at which it will ignite in air.

Weather

While temperature, moisture and wind all determine the nature of a fire, it is wind that typically pushes fire and determines the speed and direction of the flames.

According to Shanley, the initial stages of the Rocky fire included a plume that contained massive amounts of fire, smoke, heat and energy. Once a plume collapses, it spreads the fire and energy outward and “the plume itself becomes the agent of dispersion,” Shanley said.

With enough heat, fires can create their own weather patterns, making it difficult to predict how the fire will behave and to decide where to send crews and equipment.

As the Rocky fire has gotten larger, “it has started to generate its own wind, and it will travel where its own wind wants to go,” said Daniel Berlant, Cal Fire spokesman.

Winds generated by fires have the potential to blow faster and harder than ambient winds. “The winds among fires are atmospheric extremes,” said Janice Coen, project scientist at the National Center for Atmospheric Research. “If you were standing near one, the winds may be so strong you could be knocked out.”

Topography

The land east of Clear Lake is very hilly and steep – “not good for the fire and not good for firefighters,” Shanley said.

Fire travels faster uphill than downhill partially because heat rises, preheating the area for engulfment.

The fire has also reached parts of Berryessa Snow Mountain, which was recently designated as a national monument. The North American tectonic plate and Pacific plate intersect in the area, said Bob Scheider, senior policy director of Tuleyome, a land conservation group. Over the eons, the shifting of the plates has created the steep mountains and valleys that have made the Rocky fire so difficult to fight.

Katie L. Strong: (916) 321-1101, @katielstrong

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