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A four-day-long heat wave that blasted the Bay Area with its first shot of summer air gave way Friday morning to a lower-pressure system that began nudging the heat-creating ridge of high pressure out of the region and allowing the region’s natural air conditioning to blow.
Fog along the coast returned, cool morning breezes reached far areas inland, and temperatures were expected to be 8-15 degrees cooler in cities throughout the region than earlier in the week.
“What we had overnight and into (Friday) was completely marine-layer induced,” National Weather Service meteorologist Dylan Flynn said. “The ridge was compressed and keeping it very close to the coast. But as the high pressure moves east, the marine layer isn’t so compressed. It’s able to move out, and a lot more of the area can feel it.”
The migration of the two systems — the high pressure being bumped to the east and the lower pressure arriving from the coast — actually began Thursday, with temperatures down 5-6 degrees from the previous day. The thermometer reached 92 in Concord. It peaked at 91 in Livermore, 83 in San Jose and 81 in Redwood City.
They will dip significantly on Friday. A heat advisory that had been in effect for much of the region since Tuesday and the Santa Cruz Mountains since early Thursday was no longer active Friday morning.
The hottest spot in the region Friday was forecast to be Brentwood in far east Contra Costa County at 91. Elsewhere, Livermore is expected to top out at 84, Concord at 79 and San Jose at 82. In Oakland and San Francisco, the mercury likely won’t escape the 60s, Flynn said.
“We’re going to enjoy the cooler weather all through the weekend,” he said. “We’re going to have marine layer clouds, and they could even cause a little drizzle, probably not even enough to get the ground wet.”
Temperatures are likely to nudge up again come Monday, Flynn said. But he added that the “little heat event is going to be cooler” than the one that followed. That mild heat-up is expected to last through mid-week before temperatures “return to more their normal,” he said.
“This really isn’t too far off from what we would expect at this time of the year,” he said. “We haven’t gotten to our peak heat time yet.”