LOS ANGELES - Excessive heat warnings began going into effect in California on Friday as forecasters predicted that high pressure building over the western U.S. would send temperatures soaring to dangerous levels during the long Labor Day weekend.
Initial warnings issued for Southern California's valleys, mountains and deserts were expected to expand out to the coast and into Northern California by Saturday.
A "brutally hot" four days are in store, the National Weather Service wrote.
Downtown Los Angeles was forecast to reach 107 degrees (41.6 Celsius) on Saturday and 108 on Sunday (42.2 Celsius). Napa in the wine country could reach 113 degrees (45 Celsius), and Palm Springs could reach 120 (48.8 Celsius).
Fleeing to beaches, mountains
The forecasts brought calls for Californians to conserve electricity and raised concerns that people flocking to beaches or mountains to escape the heat could spread the coronavirus.
The rush was already on in the popular San Bernardino National Forest east of Los Angeles, where high elevations and lakes offer respite.
"I got a note that most of the campgrounds in the San Bernardino mountain range are already full and I expect them to be completely full within the hour," forest spokesman Zach Behrens said at midmorning Friday.
The California Independent System Operator, which runs California's power grid, issued a "Flex Alert" for the hours of 3 p.m. to 9 p.m. Saturday through Monday, asking people to conserve power by not using washing machines and other appliances during the period and keeping their air conditioners at 78 degrees (25.5 Celsius) or above.
"We're not forecasting any blackouts" at the moment because of the heat, but the power system could be strained by unforeseen problems, such as a fire that disrupts a power line, Cal ISO Operations Vice President Eric Schmitt said.
Cal ISO also ordered power generators to postpone routine maintenance and restore any out-of-service transmission lines.
Governor Gavin Newsom declared a state of emergency Thursday night, temporarily suspending certain pollution regulations and permit requirements for power plants so that they can produce more electricity.
The power concern follows a mid-August heat wave that strained the grid to the point where Cal ISO ordered utilities to implement brief rolling blackouts for the first time since 2001. Officials said customers' conservation significantly helped.
"It was an important factor indeed," Schmitt said. "We're asking for that kind of support again as we go into this weekend."
The heat also was expected to hike ozone levels, resulting in poor air quality throughout a Southern California area that is home to nearly 20 million people, air regulators warned. Bay Area air quality was also expected to suffer again from wildfire smoke.
Authorities, meanwhile, hoped to prevent a surge in COVID-19 infections that could occur if people engage in traditional Labor Day weekend activities.
Labor Day holidaygoers were urged to wear masks and avoid large gatherings.
COVID-19 infections spiked in many counties after the Memorial Day weekend and again over the Fourth of July weekend as people held social gatherings or packed recreational areas.
Los Angeles County, the nation's most populous, did not plan to close beaches. But health authorities warned that could happen if they become too crowded, and masks will be required when people are out of the water.
Up the coast, Santa Barbara County planned to allow use of the water and active uses of the beach such as running or walking but no sunbathing. Monterey County said people could cross the sand to reach the water but otherwise barred the use of beaches.
Such measures were not in place on the entire coast. Surfing mecca Huntington Beach, for example, was keeping its famous shoreline fully open.
The brewing heat wave was also expected to bring another challenge to thousands of firefighters who have been making progress on numerous wildfires, including massive complexes of multiple fires ignited by lightning last month in the San Francisco Bay Area and wine country.
The fires have destroyed nearly 3,300 structures, including homes, and there have been eight deaths.
The high-pressure system could produce hot, gusty winds that along with the heat will produce "elevated or near-critical fire weather," according to a weather service forecast for Southern California.
In the San Bernardino National Forest, fire crews will be on 24-hour shifts and extra crews also will be placed where they can quickly respond.
Behrens, the forest spokesman, said that with few things to do during the pandemic, people have been flocking to the mountains all summer. Many have never camped before, putting a strain on rangers to keep things under control.
Illegal campfires and barbecues outside specifically designated sites were a particular concern. Behrens said rangers planned to be out in force all weekend on "marshmallow patrols."