Santa Rosa, Napa, Concord, Livermore and areas south of San Jose will see temperatures in the 90s and up to 100 degrees on Thursday, Friday and Saturday, meteorologist Steve Anderson said.
Areas around the San Francisco Bay will be in the 70s and 80s, while coastal regions will see highs in the 60s.
"The good news is, temperatures won't be hot at the coast. The bad news is, temperatures won't be warm at the coast," Anderson said.
Wednesday will be warm but not as hot as the rest of the week, he said.
A Spare the Air advisory has been issued for the Bay Area on Thursday. Additional Spare the Air days may occur on Friday and Saturday, according to the Bay Area Air Quality Management District.
During Spare the Air days, residents are encouraged to cut back on polluting activities, including driving and using gas-powered lawnmowers. Those with respiratory issues should limit their time outdoors.
The hot weather also heightens fire danger, particularly in areas with dry grass or brush, Cal Fire spokesman Dan Berlant said. Campers and hikers should be especially careful when using fire in brushy areas, he said.
Those sticking close to home are also advised to be vigilant.
"One of the common causes of fires at home is equipment use, such as lawnmowers or weed-eaters," Berlant said. "On a hot day, especially when it's windy, it's easy for a mower blade to strike a rock and spark a fire on dry grass."
Temperatures should begin to cool off on Sunday, Monday and Tuesday, according to Anderson.
In the meantime, he said, "If you're east of the hills and you're getting too hot, just head over the hills and you can cool off."