“The heat wave will pose a high to very high risk to the general population, particularly the elderly and those without adequate air conditioning, due to both the intensity of the high temperatures and the duration of the heat wave,” the weather service warned. More than 45 million people were under a heat watch for most of Washington, Oregon, Idaho and Nevada and parts of Utah, Arizona and California. The heat was so intense that millions of Californians were again told to reduce their electricity consumption between the hours of 4 p.m. to 9 p.m. on Friday to protect the power grid.
California’s Independent System Operator — which manages 80 percent of the state’s electricity grid — issued its third Flex Alert of the week, asking residents to watch their electricity usage. “Flex Alert covers that time of day when the grid is most stressed by higher demand and less solar power,” the operator explained. The operator also asked residents to pre-cool their homes before 4 p.m., then set their thermostats to 78 degrees Fahrenheit during off-peak hours and avoid charging their electric vehicles. California cities including Los Angeles, Redding, San Diego, Sacramento, Palm Springs and Fresno could see temperatures as high as 116 degrees, according to CNN meteorologist Robert Shackelford. Similar temperatures are expected in Phoenix, Arizona and Las Vegas, Nevada. Many jurisdictions, including Los Angeles, Santa Barbara, Orange and Fresno counties, have opened cooling centers. Officials have also compiled a list of all the cooling centers in the state. Temperatures as high as 105 degrees may be seen in Reno, Nevada. Boise, Idaho? and Spokane, Washington state.

Because this heat wave is different

High summer temperatures have been the norm in California, but what makes this heat wave especially dangerous is how long it’s forecast to last across much of the state. In addition, little relief is expected during the night. “Even after the sun goes down, the heat can be a real danger — especially in big cities. Dark sidewalks and buildings are very effective at absorbing heat,” the Los Angeles weather service office said. And that’s why warmer temperatures are more common in big cities, which makes them prone to becoming an “urban heat island,” the agency explained. The weather service defines a heat wave as a period of unusually hot and humid weather lasting more than two days. Extreme heat has killed more people than any other extreme weather event in the US. Heat deaths have outnumbered hurricane deaths by more than 15 to 1 over the past decade, according to data tracked by the National Weather Service. Climate change is forcing conditions that make extreme weather events deadlier and more common. In Arizona, where temperatures are expected to reach triple digits this weekend, 111 people have died of heat-related complications this year in Maricopa County as of Wednesday, according to a county public health department report. The report says 38% of the deaths were in people aged 50 to 64, and 80% of the deaths occurred outdoors. CNN’s Paradise Afshar, Taylor Romine and Alaa Elassar contributed to this report.