What Triggers PG&E Public Safety Power Shutoffs?
SACRAMENTO (CBS13) — For weeks we've been dealing with fires and periods of triple-digit heat, but this week we are facing our first potential Public Safety Power Shutoff of the season. Why now? Along with the heat wave, this week the region will also experience its first significant off-shore wind event of the season.
The National Weather Service has issued a red flag warning due to low relative humidity and wind gusts forecasted up to 50 mph.
Realistically, power lines should be able to withstand 50 mph gusts, which has some wondering what else utilities consider before issuing a Public Safety Power Shutoff.
"The utilities have different tools at their disposal," explained Craig Clements, Director of The Wildfire Research Center at San Jose State. He noted that wind gusts and relative humidity are just a couple of the elements utilities consider before cutting off the power. They don't just rely on the "typical weather forecast."
"They have customized forecast platforms, numerical models that are very high resolution that can forecast the winds in a very specific, localized regions. In addition to looking at fire danger and fire potential, each utility has their own set of tools that are state of the art science," he said.
In short, while the National Weather Service forecasts general fire weather conditions, PG&E meteorologists are forecasting specific fire potential.
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In addition to low humidity and wind speeds, PG&E must take into account localized fuel moisture content — the dry brush and trees — and local topography like valleys, canyons and peaks, which can create microclimates with locally higher wind gusts.
Brett Edwards, a career meteorologist at PG&E, explains the utility has a proprietary Fire Potential Index (FPI) along with an outage-producing wind model that can provide much more detail than traditional weather models.
"We can narrow it down to as much as one canyon compared to the other, one side of a ridge, compared to the other. We can get that very fine detail and help us determine where the absolute need to turn off the power is," Edwards said.
PG&E says it has installed more than 800 weather stations, most in high fire-threat areas in Northern and Central California, with a goal to deploy 1,300 by next year.
As of Monday, models were indicating the greatest concern, and highest winds, would occur Tuesday morning in the foothills, sierra, and the North Bay mountains.
Edwards says, this week, dry vegetation, fuel for the fire, is one of the biggest concerns. The extreme heat combined with forecasted downslope winds, which are also drying, will be a significant factor in the PSPS forecasting.
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As for the infrastructure, while the power lines are built to sustain 40-50 mph winds, Edwards points out that the trees around them are not always as strong.