California heat wave: How long will it last?

For the second consecutive day, temperatures on Wednesday will hover over 100 degrees in many inland areas in California including in Bay Area cities including Santa Rosa, Calistoga, Livermore, Cupertino and beyond.

The National Weather Service predicts similar triple-digit temps for the July 4 holiday and at least until Saturday. Computer models show that average Bay Area summer temperatures won't return until July 13. 

The torrid conditions were being caused by a ridge of high pressure just off the West Coast and a separate ridge that spawned heat warnings and advisories from Kansas and Missouri to the Gulf Coast states, according to the NWS, 

California’s capital, Sacramento, was under an excessive heat warning expected to last until Sunday night, with temperatures forecasted to reach between 105 degrees and 115 degrees.

Southern California's temperatures were also "exceptionally dangerous," forecasters warned. 

The worst of the heat will be centered in California’s Central Valley, where as many as 10 days or more of 110-degree heat looms. But just about all of California, stretching into southern Oregon and western Nevada, will swelter for an extended period.

KTVU meteorologist Roberta Gonzales said the weather might cool down by 10 degrees or so on Monday, but then temps will be in the 90s next week. 

"We haven't experienced anything like this in a decade because of the prolonged nature," Gonzales said. 

She said that temperatures are currently about 20- to 25-degrees above normal, with coastal Pacifica even reaching 75 degrees. 

"The heat’s brutal," said Grant Taggart of Santa Rosa said on Tuesday, when the temperature was 107 degrees. "I have the air conditioner out. Spent some time at Russian River. Walked down to the ice cream shop. I got to make the most of it."


Excessive heat: These Bay Area cities will soar past 100 degrees

California and parts of the West are smack-dab in the middle of a prolonged and excessive heat wave that's not expected to cool off until at least the weekend. Lots of cities are seeing temps of over 100 degrees.

The hot weather and Red Flag Warnings had firefighters on edge.

In Calistoga, state firefighters raced to quell a wind-driven vegetation fire, which they contained to about 50 actress off Old Lawley Toll Road. 

And the Thompson Fire up north in Oroville also broke out on Tuesday, scorching more than 2,000 acres and prompting 13,000 evacuations. 

Fire danger was such a concern in St. Helena, that the Napa County city canceled its July 4 fireworks show. 

The heat wave on Tuesday also prompted Pacific Gas & Electric to proactively shut off power to 12,000 customers in parts of 10 counties to prevent wildfires from being ignited by downed or damaged electrical wires.

Many cities were trying to help residents stay cool and open centers where people could go if they didn't have air conditioning. 

Richard Ramirez, who lives out of his van in Martinez, said he drove to the Concord Senior Center, which became a cooling center, to charge his devices, and escape the oppressive heat for much of the day.

"It's very hot, I'm not going to lie, it's very, very hot, I actually just had to walk to Safeway earlier, and it was scorching," he said. "I was just melting, it felt like my feet were on fire." 

For a list of cooling centers in the Bay Area, click here. 

The Associated Press and Fox 11 contributed to this report.