For days, a historic Bay Area heat wave that broke century-old records appeared finally to be shoved out the door like a bar patron who’s had too much to drink.
Instead, it has turned around and is back pounding on the region, insisting on one more round.
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“This is still the high pressure that started everything. It shifted slightly off to the east for a couple of days,” National Weather Service meteorologist Roger Gass said Wednesday. “The ridge is just building again.”
The system led to five straight days last week of temperatures exceeding 100 degrees in the hottest places, as well as the longest excessive heat warning in the region’s history. This final blast won’t be as intense or long, the weather service said. The heat is back from 11 a.m. Wednesday until 8 p.m. Friday for 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.
The weather service also issued a heat advisory for the Santa Cruz Mountains and along the North Bay Coast.
A Spare the Air Alert also was in effect Wednesday. Air quality in far inland areas of the East Bay and in the Santa Clara Valley was expected to be unhealthy for the very young and elderly, as well as those with heart, respiratory or other conditions. Where it’s not unhealthy, the air is expected to be only moderately healthy.
The hottest temperatures in the region are expected to peak between 104 and 107 degrees on Wednesday, according to the weather service. In areas, not quite as far in the interior, the weather service said the gauge would run from 95-100. The hotter areas along the bay coast and in the Peninsula will peak in the low-to-mid 80s, and San Francisco will get into the 70s.
On Thursday, the thermometer is expected to run just as hot in the cooler places and perhaps 3-5 degrees higher in the hottest spots.
“We’ve got an incoming trough aloft that is shifting the flow of the high pressure back to us,” Gass said.
The high-pressure ridge that Gass said has begun to “rebuild itself” won’t become as thick and powerful as it did the first time, he said. He added that the marine layer also continue to have a strong influence than when temperatures built during the system’s peak.
Thick coastal fog appeared in the region for the third straight day, and Gass said the on-shore flow of cool marine breeze that creates the region’s natural cooling system is unlikely to shift.
By Friday, Gass said temperatures will creep back down cooler than Wednesday. By Saturday, few places in the region are forecast to reach even 90.