 Bloomberg -- As many as 10 million Californians averted what would have been an unprecedented series of rolling blackouts Monday night after temperatures fell, people turned down air conditioners and officials called off the outages.They may not be so lucky on Tuesday. The heat wave thats pushing the regions power grid to the brink is continuing with vengeance. Sacramento is forecast to hit 109 degrees Fahrenheit 43 degrees Celsius. Los Angeles will climb to 97, up 10 degrees from a day earlier. If those projections hold, the threat of rotating outages will loom.Since Friday, millions of Californians have seen their lights abruptly cut with little notice -- part of a last-ditch effort by the states grid operator to save the system from cascading power failures. The outages have drawn criticism from industry experts who say they werent necessary, prompted California Governor Gavin Newsom to open an investigation and raised questions about the reliability of the states grid, which has become increasingly dependent on intermittent solar and wind generation in recent years.Let me just make this crystal clear: We failed to predict and plan these shortages -- and thats simply unacceptable, Newsom said in announcing the probe.In the case of Monday, however, it was arguably a matter of over-planning.By 2:30 p.m. that day, grid manager California Independent System Operator was warning that an unprecedented 3.3 million homes and businesses could see their power go out. Thats up to 10 million people, or a quarter of the states population, based on the average household size. A few hours later, the agency scaled back its plans to hit about 1 million customers. Then it delayed the start of the outages.And just before 8 p.m., it lifted an emergency declaration altogether.The grid operator credited cooler-than-expected weather and electricity demand that came in lower than projected.We are grateful to families and businesses across the state that answered the call to reduce electricity use, Steve Berberich, the president and chief executive officer of California ISO, said in a statement. The heat storm is not over, and we still expect exceedingly hot temperatures on Tuesday and Wednesday, he said.This month is the first time California has resorted to rotating outages since the 2001 energy crisis. And it couldnt be hitting the region at a more vulnerable time, with the pandemic forcing people into lockdown, leaving them with little choice but to endure the heat indoors. The cutoffs have been reminiscent of the mass blackouts that utilities carried out less than a year ago to keep their electrical lines from sparking fires during unusually strong windstorms -- all extreme weather events made more frequent by climate change.But even last years outages wouldve paled in comparison to the one that had been planned for Monday. Rarely if ever have 3.3 million homes and businesses across California been affected by a planned shutdown of this kind.One thing that has made Californias grid so vulnerable to soaring demand is the states rapid shift away from natural gas. About 9 gigawatts of gas generation, enough to power 6.8 million homes, have been retired over the past five years as the state turns increasingly to renewables, according to BloombergNEF. That leaves fewer options when the sun sets and solar production wanes.Normally, California can import enough power from neighboring states when supplies are tight. But the sprawling heat wave blanketing the U.S. West is pushing power plants to the hilt across the region.California is in a tight spot, BNEF analyst Brian Bartholomew said. Its retired a lot of gas. And the storage thats supposed to help hasnt yet come online.Read More: Blame Climate Change for Heatwave Misery: Green InsightThe relentless heat is also starting to take a physical toll on Californias power system. Transformers -- the metal cylinders sitting atop power poles -- can malfunction and catch fire if they dont cool off at night. And temperatures in some parts of Southern California are expected to remain in the low 80s overnight. During a deadly, 10-day heatwave in 2006, the states utilities lost more than 1,500 of these devices, with each knocking out service to one neighborhood in the process.The heat wave gripping the West Coast stems from a stubborn, high-pressure system that has parked itself across the Great Basin spanning Nevada and other western states. It essentially acts as a lid trapping hot air, and there arent any indications its going to budge soon.Such phenomenons, sometimes called heat domes, are getting worse because the Earths climate is changing. As the planet warms, the contrast between the heat at the equator and the cold at the pole decreases. That saps the strength of the jet stream, which otherwise would be able to shove the ridges out of the way. It explains in part why extreme heat has blanketed regions around the world in recent weeks.Read More: Japans Heat Wave Matches Record as Tokyo Death Toll Rises to 53Extreme weather has taken a profound toll on electrical grids in recent weeks. Earlier this month, millions of people lost power across the U.S. Midwest after a wall of lightning, hail and deadly winds tore a path of ruin from central Iowa to Chicago. Days earlier, Tropical Storm Isaias darkened millions of homes from the Carolinas to Connecticut.Updates forecast in the second paragraphFor more articles like this, please visit us at bloomberg.comSubscribe now to stay ahead with the most trusted business news source.2020 Bloomberg L.P. 