A Bay Area heat wave that got its start more than a week ago unveiled its final encore on Thursday before the curtains were expected to begin closing on it for good.
“One more day of really, really hot,” National Weather Service meteorologist Alexis Clouser said.
“Really, really hot” has been the ongoing theme in the region since the barometer showed high pressure building on July 1. On Thursday, most of the Bay Area’s interior reached at least 100 degrees and at least one city hit 111, making it the hottest day since the high-pressure ridge began to rebuild itself earlier this week.
That ridge was responsible for the heat wave that lifted temperatures into the upper 90s and 100s throughout the region six times after July 1.
An excessive heat warning that started Wednesday remained in place through Friday at 8 p.m. The areas under the warning are the East Bay hills and interior valley areas, San Jose and the Santa Clara Valley, the Eastern Santa Clara hills, and the North Bay interior mountains. A heat advisory for areas further south and north also was in place.
On Thursday, Livermore reached 111 degrees, tying its previous record set in 1961, according to the weather service.
Other highs around the region included 108 degrees in Concord, 101 in Napa, 99 in San Jose, 96 in Hayward, 92 in Redwood City, 84 in Oakland and 74 in downtown San Francisco.
The heat caused BART to run trains on its tracks slower than normal, a routine move on that commuter system since the temperatures skyrocketed.
It also came with dirty air. A second straight Spare the Air Alert remained in place, with air quality around much of the interior part of the region expected to be unhealthy for sensitive groups, including those with health issues. A new alert for Friday had not been issued as of 3 p.m. Thursday.
Clouser said the extreme heat Thursday would have stayed longer if the high-pressure ridge were still as strong as it was a week ago. Instead, it is not as compressed or thick, because it’s the back edge of the system. The high pressure will move significantly to the east on Friday and Saturday, allowing a marine layer that was again becoming compressed to open fully.
The undoing of that compression will open the door to a new weather system that will be welcome for the region. Temperatures will start moving down Friday — temperatures still will be in the upper 90s, and perhaps top 100 in the hottest places — before the cooler vibe kicks in on Saturday.
“We have a decent stretch of stratus (clouds) off the coast, and that’s gonna continue to have influence,” Clouser said. “But once we get to Saturday, you’re gonna see a real significant drop in temperatures and conditions will start to set in that are normal for this time of year.”
That system will set firmly into place by Sunday, according to the weather service. Only a handful of cities are expected to reach 90 degrees.
“Once we get cool, for the next week or so it’s pretty calm,” Clouser said. “We’re not really looking at anything at the moment that appears to be too impactful. Temperatures are going to be normal. It should be comfortable.”
Staff writer Jason Green contributed to this report.