The respite from a heat wave that set records didn't prove to be a very long one, with forecasters on Wednesday saying that a high-pressure ridge is strengthening and that temperatures will jump back up into triple-digits in the hottest areas by Thursday.
"The air mass is stagnant," National Weather Service meteorologist Roger Gass said Wednesday. "That's causing the on-shore flow to weaken, and that's going to allow those temperatures to ramp back up."
The dry heat also will fuel fire danger in a state that has seen major wildfires burning throughout it since August. Firefighters locally were aided as winds died down, but the Glass Fire across Napa and Sonoma counties continued to consume acres and spread. It was 2% contained early Wednesday and had burned 75 square miles.
The National Weather Service issued a fire weather watch for Thursday beginning at 1 p.m. and running through 6 p.m. Friday for areas around the Glass Fire and the North Bay mountains. Winds about 10-20 mph will blow consistently, and gusts as high as 25-30 mph may be felt at the highest elevations, forecasters said.
The heating-up process will start on Wednesday, with temperatures in the far inland East Bay expected to touch 100 degrees in places such as Livermore and Antioch and get as high as 98 in Walnut Creek and Concord.
Areas along the coast probably won't hit the 90s until Thursday, forecasters said, and other areas may end up just shy of the 100-degree mark on Thursday. San Jose was expected to get as high as 88 degrees on Wednesday and 95 on Thursday, and Hayward is expected to reach 86 and 91, respectively. The heat wave's peak likely will lift the temperature by Thursday to 86 in Oakland; 79 in San Francisco, and 75 in Pacifica.
The heat and the stagnant air mass may also combine to lower the air quality. A Spare the Air day through Friday remained in effect, and the official air-quality index readings were expected to approach unhealthy levels in the North Bay, according to the Bay Area Air Quality Management District.
The air through the region still was mostly good by 7 a.m. Wednesday, with only West Oakland (72), East Oakland (62), Pleasanton (55), Livermore (54) and Berkeley (52) showing readings from 51-100, which means moderately unhealthy air. The rest of the region, including the North Bay region, had good air, according to the district.
By Friday, the air is at least expected to be cooler, forecasters said.
"We see this peaking on Thursday," Gass said. "The high pressure is going to begin to break down, and you're going to get some westerly winds and a more persistent on-shore flow, and that'll cool it off."
Distributed by Tribune Content Agency, LLC.
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