Bay Area heat expected to ease during week
A high-pressure “heat dome” that expanded over California this weekend will finally meet some resistance this week, bringing welcome cooling across the Bay Area.
In the Bay Area, temperatures that were expected to soar over 100 degrees in Brentwood and into the mid-to-high 90s in the rest of the region’s hot spots Monday were forecast to come down 10 to 12 degrees overnight, thanks to a low-pressure system descending from the Gulf of Alaska.
The intersection of the two systems will happen from Tuesday through Thursday, said National Weather Service meteorologist Drew Peterson, and “cause the heat dome to be compressed and that’s going to create the cooler conditions.”
“Picture somebody in football who’s running and all of a sudden here comes a defender who delivers a blow,” Peterson said. “That’s what you’re going to see here with this heat dome that’s been expanding.”
On Monday, the region struggled through one more day of gradually increasing temperatures, part of a heat wave that began late last week. The thermometer was expected to rise to 102 degrees in Brentwood, 97 in Pittsburg and 95 in Concord, according to the weather service. In the South Bay, it was forecast to reach 97 in Morgan Hill and 90 in San Jose.
Still, the expected lower temperatures later this week are unlikely to provide firefighters battling a blaze in Yosemite National Park with much of a reprieve. The Washburn Fire, which broke out south of the Merced River, increased to 2,340 acres on Monday as firefighters tried to stop the flames from spreading across the dry landscape and reaching the park’s largest stand of ancient sequoias.
“The changes we’re going to see over the next few days are going to be marginal, so it’s not going to do much to impede the fire,” said Andy Bollenbacher, a meteorologist for the National Weather Service.
And on Friday afternoon, forecasters are predicting a chance of thunderstorms in the Sierra Nevada above 8,000 feet of elevation.
“Unfortunately, that could lead to more fire starts,” Bollenbacher said.
Smoke from the Washburn fire prompted the Bay Area Air Quality District on Monday to issue an air quality advisory, though most of the smoke hovered at elevated altitudes, affecting visibility more than breathing, according to Aaron Richardson, spokesperson for the district.
By Monday afternoon, some of the air quality index readings of fine particulate matter by the Bay Area Air Quality Management District had exceeded 50, putting them into the moderately unhealthy category. Those readings were mostly in areas of Oakland, the western area of Contra Costa County, San Jose and Sebastopol. The air quality throughout the rest of the region remained below 50 and good.
There was unhealthy air in eastern parts of Contra Costa County early Monday, because of smoke from the Marsh Fire near Pittsburg.
The low-pressure system and on-shore breeze coming to the Bay Area on Tuesday are expected to push any lingering smoke out of the region, Richardson said.
“We’re not expecting to see impacts after today, but we’re keeping tabs on the situation toward the end of the week,” Richardson said.
The temperature cool-down that is expected to start Tuesday — forecast highs are 95 in Brentwood, 86 in Pittsburg and Morgan Hill, 84 in San Jose, 83 in Concord, 71 in Oakland and 68 in San Francisco — is expected to remain in place at least until Friday, Peterson said. But by mid-day Friday, a higher-pressure system the weather service is tracking from the southeast could meet up with another low-pressure system from the Gulf of Alaska, causing another heatwave.
Meanwhile, the threat of new wildfires sparking and fires already burning across the state growing may intensify going into the weekend thanks to rising temperatures and a possibility of thunderstorms.