By themselves, the National Weather Service’s forecasted Tuesday highs for the Bay Area were telling enough about the power and unusualness of an October heat wave that is set to go full throttle Tuesday and Wednesday.
In Alameda County: 104 degrees in Pleasanton, 103 in Livermore and 96 in Oakland. In Contra Costa County: 104 in Concord, 103 in Walnut Creek, 101 in Lafayette and 102 in Antioch. In Santa Clara County: 103 in Morgan Hill and 101 in San Jose. In San Mateo County: 94 in Redwood City and 92 in San Mateo. In San Francisco: 91.
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Add to those figures the explanation for what’s happening, and the latest heat takes on an even more powerful look.
“One of the thresholds we look at is what the temperature is above the surface — about 5,000 feet or so over it,” NWS meteorologist Dylan Flynn said. “It hasn’t been this hot that far above the surface since 1980. The upper air high pressure just continues to be build, and the off-shore winds are bringing that heat all the way to the coast.”
So it is that some records were set to fall or be threatened, many of them set when Ronald Reagan was running for the presidency for the first time. That said, some areas that on Monday appeared ready to approach records — San Rafael and Kentfield in Marin County — are unlikely to crack triple-digits as originally anticipated, according to the weather service.
Still, new marks could be tied or set in Livermore (previous record 102 in 1952) San Jose (97, 1980), Santa Rosa (102, 1980) and Half Moon Bay (83, 2014), according to the weather service.
San Jose tied a record previously set in 2001 when it reached 95 on Monday, the weather service said. San Rafael also set a mark, reaching 102 to surpass by 1 degree its 1980 figure.
More of the same is also likely on Wednesday.
The two days “are basically going to copies of each other,” Flynn said, “The system is starting to get a long tail though. So it’s going to extend through the weekend in the hotter inland places. It might not be quite as hot as it will be Tuesday and Wednesday, but it will be hot.”
A heat advisory issued by the weather service that went into effect Monday morning was set to remain in effect through 11 p.m. Wednesday. The weather service on Tuesday added San Francisco to the list of cities included within that advisory from 10 a.m. to 8 p.m.
The high ceiling on the high pressure also created the dynamic for dirty air again; the Bay Area Air Management District had a second straight Spare the Alert in place for Tuesday.
Fire danger was expected to increase significantly, according to weather and public safety officials. Flynn said the weather service was considering whether to issue a red-flag warning for fire danger in certain areas.
“Winds in the mountains and other higher elevations have been higher than we originally anticipated they would be,” Flynn said. “We’ve had sustained winds of 25 mph with gusts up to 40 mph.”
Those winds also are blowing toward the water from the Northeast, another factor in keeping the area warm. That part of the heat wave is expected to subside come Thursday, along with some of the coastal heat, Flynn said.
The cooldown inland is going to be far more gradual.
“The temperatures aren’t going to fall off a cliff anytime soon,” Flynn said. “It will be least until Sunday that it feels more comfortable and maybe not until Monday or Tuesday that you see the seasonal averages.”