Flex Alert issued for Thursday when heat will spike after small dip

Onshore winds, moisture from Mexico and haze from wildfires in Arizona eased the heat wave in greater San Diego County on Wednesday. But forecasters say temperatures will tick back up as those influences fade.

And for the first time this year, the California Independent System Operator — the nonprofit that manages about 80 percent of the state’s power grid, including the San Diego area — issued a Flex Alert.

Between 5 p.m. and 10 p.m. Thursday, the grid operator — known as the CAISO — asks consumers across the state to reduce energy use to help relieve stress on the electric system.

“The current forecast for shortages is relatively modest in magnitude and there’s a good chance we can resolve them across the course of the day,” said CAISO president Elliot Mainzer. “But in a preponderance of caution we have issued the Flex Alert and we really will need the help of consumers.”

Chief operating officer Mark Rothleder said in a briefing with reporters the CAISO estimates a shortage of about 300 megawatts Thursday and issuing the Flex Alert “gives us that buffer to absorb that 300-megawatt shortfall.”

Through late Wednesday, temperatures were running 3 to 9 degrees cooler than they were a day earlier along the coast and in the western valleys, according to the National Weather Service.

The high in San Diego hit 72, a degree above normal. And Ocotillo Wells, in the desert, the figure was 108, several degrees lower than projected.

The slight respite was heavily influenced by a coastal eddy, or rotating column of air that brought cool winds ashore from the south. The eddy extended all the way from San Clemente Island to the county’s foothills.

At roughly the same time, moisture from the Gulf of California flowed into the low deserts, holding down temperatures. And the haze muted things further.

Forecasters say San Diego’s high will rise to the mid-to-upper 70s later this week while inland valleys and foothills hit the mid-to-upper 90s. Borrego Springs and Ocotillo Wells could reach 119.

Such heat is worrisome for CAISO.

Last August, California experienced two consecutive days of rotating outages when the state’s grid wilted under an intense heat wave — the first rolling blackouts in the state in nearly 20 years.

Mainzer said the current bout of hot weather is not as severe as last August’s and he has “guarded optimism” the grid will hold up better this year.

“We do think we generally are in better position than last summer,” Mainzer said, “although we have been very clear about the fact that we still have residual risk.”

Notably, drought conditions throughout the state will lead to a reduction in the number of megawatts California’s hydroelectric facilities can deliver to the grid this summer.