Triple-digit temperatures began making their return engagement — albeit, a short one — to the hottest parts of the Bay Area on Thursday, ahead of a steeper heat spike that will cover familiar areas on Friday and Saturday.
However, the high heat also won’t feel quite as intense as it did during a three-day stretch last weekend, according to the National Weather Service.
“Overall, we’re starting to get the more consistent summer-time temperatures, so people and their bodies are having some time to adjust to it,” NWS meteorologist Sean Miller said Thursday morning. “Also with this one, we’re only going to heat up for day or two. It’s not going to stay warm at night. So it just won’t be quite as intense. It’s still gonna be hot.”
A heat advisory for the far inland areas and valley areas was set to begin at 11 a.m. Friday and run through 11 p.m. Saturday.
The Bay Area Air Quality Management District also issued a Spare the Air alert for Friday, when air in much of the region will be only moderately healthy and the air in the Santa Clara Valley will be unhealthy for those with sensitive conditions. They issued two such alerts during the previous heat wave.
An air advisory for the region — prompted by smoke from Oregon’s Flat Fire drifting into the Bay Area — was in effect for a second day Thursday.
As usual, the hottest spots were expected to be in far east Contra Costa County, with Brentwood forecast to hit 107 degrees Thursday and 106 Friday. In Alameda County, Livermore was likely to hit the highest temperatures, at 102 degrees Friday and 99 on Saturday, while Morgan Hill would provide Santa Clara County’s hottest spots at 99 degrees Friday and 96 on Sunday.
The rest of the region is likely to be far milder, Miller said. San Jose is expected to peak at 88 on Friday; Oakland and San Mateo probably won’t get into the 80s; and San Francisco will Friday and Saturday in the 60s before creeping up to the low 70s at the beginning of next week.
“There will be winds off the water during the whole thing,” Miller said. “The onshore flow will continue, and that cooling effect won’t go away.”
All of it is being created by a gigantic high-pressure bubble that is resting above the Pacific Southwest, Miller said, feeding the heat wave that is smothering large parts of the rest of the country.
That high pressure is stable and strong but occasionally contracts, Miller said. When it does, he said it influences the systems migrating from the Pacific Ocean and allows some of the heat enveloping the Bay Area to escape, which has kept the region’s recent heat waves mercifully short.
A trough approaching from the Pacific Northwest is expected to create a pattern change locally and perhaps to the bubble enveloping the southern desert, Miller said. The trough will bring temperatures back down to the 80s for most of the region by Monday, while the hottest places are likely to heat up into the low 90s.
Miller said those temperatures are expected to remain steady for at least a week.