Officials investigating the roles of wind and power lines in Northern California wildfires

There is no doubt that after numerous wildfires started Sunday night October 8 north of San Francisco the very strong winds caused them to spread so rapidly that there is no way firefighters could put them out before they grew large. There are reports that the Tubbs Fire between Santa Rosa and Napa burned about 20,000 acres in a few hours.

Many power lines blew down or sparked as electrical conductors brushed together in Sonoma and Napa Counties.

According to the Mercury News:

Emergency dispatchers in Sonoma County received multiple calls of power lines falling down and electrical transformers exploding. In all, according to a review of emergency radio traffic by the Bay Area News Group, Sonoma County dispatchers sent out fire crews to at least 10 different locations across the county over a 90-minute period starting at 9:22 pm to respond to 911 calls and other reports of sparking wires and problems with the county’s electrical system amid high winds.

Officials have not released the causes of most of the fires, but the stock price of Pacific Gas and Electric which supplies electrical power to much of the area dropped 22 percent last week.

Stock price of PG&E
Stock price of PG&E, last two years. CNBC graphic.

On Monday the Cliff Mass Weather and Climate Blog, an excellent source for in-depth analysis of weather events, looked at the conditions that led to the extreme winds when the fires started. Here is an excerpt:

…Although there have been a lot of media reports about windy conditions, few have described the extreme, often unprecedented, nature of the winds on Sunday night and Monday morning (October 8/9th).   Some have even mocked PG&Es claims of hurricane-force winds, suggesting wind speeds of 30-40 mph.

Let’s clarify a few things.  There was a wide range of winds that night, with the strongest winds on ridge tops and on the upper lee slopes of terrain.  Some winds was startling.

For example, at 10:30 PM on 9 Oct 2017 the wind gusted to 96 mph on a 3400 foot peak NE of Geyersville, about 20 miles NNW of downtown Santa Rosa. They reported sustained 74 knots (85 mph).  Those are hurricane force winds (sustained of 64 knots or more).

At the Santa Rosa RAWS station (U.S Forest Service and Bureau of Land Management) at 576 ft elevation, the wind accelerated rapidly Sunday night to 68 mph.

wind forecast northern california fires
Desert Research Institute’s forecast model (WRF) at very high resolution (2-km grid spacing). This is their 6-hour forecast for sustained surface winds at 11 PM Sunday October 8. Click to enlarge.

San Diego Gas and Electric (SDG&E) is still battling over who will pay for the destruction, the company or their customers, caused by the Witch Creek, Guejito, and Rice Canyon fires in 2007 that started from issues with their power lines. The fires destroyed more than 1,300 homes in southern California, killed two people, and caused massive evacuations. The Witch Creek Fire alone, which started near Santa Ysabel, burned 197,990 acres.

In 2009 SDG&E proposed to implement a system of completely turning off power preemptively to areas where very strong winds are predicted.

Author: Bill Gabbert

After working full time in wildland fire for 33 years, Bill Gabbert now writes about it from the Black Hills.

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