Well into the summer months, the Bay Area can expect its first real heat wave of the season, with inland cities like Livermore and Morgan Hill expected to experience the region's most sweltering temperatures as experts keep a close eye on the state's power grid to ensure it can weather the weather.

The non-profit that manages the state's power grid is asking people to limit their power usage between 11 a.m. to 6 p.m. through Sunday in anticipation of near-record electrical consumption. And a "Spare the Air" warning has been issued for Friday.

A high-pressure system is bringing the heat, said National Weather Service meteorologist Austin Cross. There will be relief by the end of the weekend, but residents will first have to brave temperatures expected to break triple digits in areas that don't have the benefit of shoreline breezes.

"There will be some cooling off toward the latter half of the weekend, Sunday into Monday," Cross said. "But the worst will be Friday into Saturday."

Livermore is anticipated to reach a high of 102 degrees in the next couple of days, and Morgan Hill and Brentwood are expected to top 100 degrees. Cities like San Jose, Hayward and Fremont will experience typical August temperatures in the upper 80s, while San Franciscans will be bypassed for the most part with highs in the low 70s.

Still, the region's max highs were enough to prompt meteorologists to issue an alert.

"These are the first really warm days of the season, and it's why we're highlighting it," Cross said.


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Warm temperatures are expected to persist into the fall, Cross said, in the typical fashion of a lingering "Indian summer."

Cross said rural areas and popular hiking spots like Pinnacles National Monument will experience the hottest temperatures, and residents and hikers should take heed by keeping plenty of water on hand.

No records are expected to be broken this weekend, but the California Independent System Operator Corporation, a nonprofit that governs 80 percent of the state's power grid, is preparing for an anticipated surge in power consumption expected to get close enough to the all-time usage high reached in 2006, when 50,270 megawatts coursed through the system.

California ISO expected 47,125 megawatts to be consumed Thursday, 46,800 on Friday, and tapering down to 43,000 by Sunday. The agency issued a flex alert urging residents to limit their high-power consumption between 11 a.m. and 6 p.m. through the end of the weekend so that the grid has a cushion to handle any unanticipated surges.

It issued two such alerts last September, but none before that since 2008, said spokesman Steven Greenlee. No one expects the grid to be overwhelmed this weekend, but in light of more heat expected later in the season and a decrease in resources -- such as the offline San Onofre plant previously relied on for 2,250 megawatts -- officials want to have some energy capacity in reserve.

"Supplies are now tightening, so we need to think of conservation," Greenlee said. "We're getting to the point now where take this flex-alert step to ensure there's enough to go around."

Meanwhile Bay Area air-quality officials issued another "Spare the Air" Friday, following one for Thursday.

The warnings are aimed to discouraging high-polluting activities like driving and using other high energy-consuming appliances like lawn mowers during times of high heat and low winds, which combine to produce high ozone levels and poor air quality.

"Several more hot days are forecast for the Bay Area and it's important that we remain vigilant about reducing our driving not just during Spare the Air Alerts, but every day to avoid unhealthy air quality," said Jack Broadbent, executive officer of the Bay Area Air Quality Management District.

Staff writer Erin Ivie contributed to this story. Contact Robert Salonga at 408-920-5002. Follow him at Twitter.com/robertsalonga.