Extreme weekend heat set to disrupt North Bay firefight and strain power grid

While the past several days of a cooling fog were helpful for firefighters battling the lightning-sparked blazes in Sonoma County and beyond, a weekend heat wave could threaten to undo some of that progress while posing the risk of more blackouts for the state’s power grid.

The National Weather Service has issued an extreme heat watch for interior regions of the Bay Area beginning Saturday and lasting into Monday, with triple-digit temperatures expected in Sonoma County and little relief at night.

Accuweather is predicting a high of 106 in Santa Rosa on the Labor Day holiday, well over the average 82 for the date and last year’s high of 77 degrees.

The heat is expected to strain the power grid, and the state’s grid operator has issued a weekend alert in anticipation of high energy demand and precautionary blackouts.

Cal Fire Division Chief Ben Nicholls said the hot and dry conditions will increase the need for Walbridge fire crews to quash smoking embers or other hot spots before they can take hold.

“The heat advisory will give an opportunity for portions of the fire that might have been less active with the marine layer we’ve been having to pop back up,” he said. “We may have smoke popping up in areas we thought were out.”

Cal Fire has staff meteorologists who advise chiefs, who then position the right amount of equipment and people in the right places.

“We still have the resources on the fire line making sure we are out there hunting out hot spots before we get those more favorable burning conditions,” he said.

Weather service forecasts call for high temperatures to begin climbing from 83 degrees on Thursday in Santa Rosa to 93 on Saturday and 99 on Sunday.

“We expect temperatures to hit triple digits over the weekend in the North Bay, with the interior easily over 100,” meteorologist Matt Mehle from the National Weather Service in Monterey.

Nighttime lows for Santa Rosa may fall to the low 60s, but in higher elevations it may not cool that much.

“You’re not seeing much in way of relief, that’s when it becomes a heat problem,” he said.

That “heat problem” could stoke both fire risk and lead to power troubles, as state electric grid regulators already are indicating that Californians should brace for potential outages over the Labor Day weekend.

The California Independent Systems Operator, which manages the grid but does not itself provide any electricity, issued an order from Saturday morning to Sunday night requiring power providers to postpone any maintenance that would necessitate outages.

An August heat wave that preceded the lightning-sparked fires brought rolling blackouts to Sonoma County and elsewhere in California. The blackouts are another burden for North Bay residents, who last year endured a series of planned power outages triggered by PG&E to prevent its equipment from sparking wildfires. A PG&E spokeswoman emphasized that PG&E and other electricity providers are expected to be at the beck and call of the Independent Systems Operator.

“When curtailment is ordered by CAISO, PG&E needs to execute it immediately and the expectation per regulation is that we are complete with the operation within 10 minutes,” Tamar Sarkissian, the spokeswoman, said in an email, adding that the PG&E doesn’t anticipate imposing public safety power outages for the next week.

"PG&E is preparing for the heat now,“ Sarkissian added. ”This includes the use of outage prediction models that help us determine the potential timing, location and number of power outages. PG&E is utilizing the latest technology to help us restore power more quickly and efficiently during a heat event.“

The “excessive heat watch” likely will be increased to an “excessive heat warning” once forecasts are hardened for the next several days.

On Sonoma County ridgetops, the evening lows may stay in the 80s over the weekend, a pattern that’s cause for concern among fire-weather experts.

“It’s going to be warm, and we are not going to get a break overnight,” Nicholls said.

Mehle noted that meteorologists look at three main things — temperature, moisture levels and winds — when considering the weather-fire danger.

On temperatures, Mehle said, “In this current pattern, the overnight lows will stay mild. Again, not a lot of relief.”

On moisture levels: “In Santa Rosa, we had fog in the morning. But in the hills, they didn’t get that. They stayed dry. The high pressure overhead, it’s going to squash down the low clouds and keep the ridgetops dry.”

And on winds: “During the weekend heat, we’re not expecting a lot of winds. So that’s one good thing.”

During most of the past 16 days, the fires have caused poor air quality throughout the Bay Area, although that has improved a bit in the North Bay.

The Bay Area Air Quality Management District forecasts clearer skies for the North Bay going into the weekend, with the air quality index slipping out of the “unhealthy for sensitive groups” category into the safer “moderate” zone.

Smoke from the August Complex fires in Mendocino County is mostly staying elevated, said Charley Knoderer, a meteorologist with the district.

Winds may push smoke from the Woodward fire near Point Reyes further to the south of the peninsula and South Bay.

“There’s been a vast improvement over the past few days for air quality,” he said. “Only isolated areas near the fires ... are continuing to see issues.”

Still, a Spare the Air alert remains in effect for the Bay Area through at least Thursday.

The heat may also become a problem for firefighters on the ground of the Walbridge fire. While crews aren’t actively battling walls of flames like they were in the beginning, the containment work they are doing these days is strenuous and exhausting.

“The hotter it gets, the more concerned we are for heat issues for our firefighters on the line,” Nicholls said. “At the incident base, they stock up on water and we have water on the engines and buses. When they head out, they plan for 24 hours at the line.”

Staff Writer Will Schmitt contributed reporting. You can reach Staff Writer Lori A. Carter at 707-521-5470 or lori.carter@pressdemocrat.com. On Twitter @loriacarter.