SAN FRANCISCO (CBS SF) — Nothing magnifies the San Francisco Bay Area’s microclimates more than a heat wave stalled over the East Bay. While the four Caldecott Tunnel bores on Highway 24 only stretch a little more than 3,700 feet, temperatures can jump 15-20 degrees when you exit the eastern end.

On Saturday, a heat wave that was driving temperatures skyward statewide had the potential to bake the inland East Bay communities — Walnut Creek, Concord, San Ramon, Danville, Livermore, Pleasanton — with readings near

“If you are in the city (San Francisco) or near the Bay, you are going to have no idea that this is an intensely hot day just over the hill for many of East Bay communities,” said KPIX 5 meteorologist Darren Peck.

The reason for the wide swing is the marine layer — wisps of fog and cooling breezes generated by cold water interacting with warm air temperatures.

What is the marine layer?

On Saturday, temperatures were predicted to climb to 106 inland, 83 in communities along the Bay and 68 degrees along the Pacific coastline.

The National Weather Service issued an excessive heat warning that remains into effect until 11 p.m. Sunday. It not only covers the East Bay, but also areas in the drought ravaged North Bay.

“Dangerously hot conditions with daytime temperatures of 102 to 110 expected,” the weather service forecasters warned. “Overnight temperatures will also remain very warm, mostly in the mid 70s, but to mid 80s in the higher elevations.”

On the edge of the Delta, Brentwood is among the East Bay communities getting scorched in this weekend’s heatwave. Residents there say the feeling is a familiar one.

“It’s always been hot out here. Lately it seems like it’s been a little hotter, a little earlier, and a little longer than it has been before,” said Brentwood local Robin Roberts. “It gets hot here, but not as much as it’s been lately.”

That’s something a lot of people were saying as the temperature soared past 100 Friday.

“Last year, and this year, it seems like, consistently, there’s more higher temperatures going on,” said Cal Fujinaga as he filled up his recycled water tank.

The latest heat wave has even longtime residents, who know heat, thinking this latest round feels a little different.

“The temperature that we’re hitting for this weekend, I don’t think I’ve seen a temperature three days in a row that’s above 106 degrees,” said Fujinaga.

Accompanying the soaring temperatures is a statewide Flex Alert issued by the California Independent System Operator (ISO) with officials calling for conservation as demands on the state’s power grid push it to the limit.

The Flex Alert went into effect Friday afternoon, originally covering high demand hours of 4 p.m. to 9 p.m. It has now been extended to cover the same time period starting Saturday afternoon.

The Flex Alert is part of Cal ISO declaring a State 1 Power Grid Emergency. Officials said that rolling blackouts are not currently part of the plan to cope with the strain on the grid; blackouts do not happen until the state hits a Stage 3 Power Grid Emergency.

“When they know that the supply is going to be tighter than expected, when they know that peak demand for energy use between the hours of four and nine pm is going to go up because of the heat. They call for rotating outages when the supply just doesn’t meet that demand and right now there’s no indication that they will call for rotating outages,” said Pacific Gas and Electric spokesperson Deanna Contreras.