More than 45 million people were warned about heat in most of California, Nevada, Washington, Oregon and Idaho and some parts of Utah and Arizona.
Forecasts call for temperatures above 100 on Friday in cities like Redding, 105; Fresno, 109; and Bakersfield, 106, in California; Redmond, Oregon, 103; and Yakima, Washington, 100.
In Nevada, Las Vegas can get 110 degrees.
“September kicks off with scorching temperatures in the western US as high temperatures are again expected to threaten daily and even monthly records en route to Labor Day Weekend,” the Weather Prediction Center said Friday morning.
“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 National Weather Service previously warned. .
September high temperature records were set on Thursday in Salt Lake City, with a temperature of 102, and in Lancaster, California, 112. Dozens of daily records were set across the region.
Millions of Californians are being urged to cut electricity consumption between 4 p.m. and 9 p.m. Friday.
The California Independent System Operator — which controls 80% of the state’s electrical grid — has issued its third Flex Alert of the week, asking residents to watch their electricity usage.
“The Flex Alert refers to that time of day when the grid is most stressed by increased demand and less solar energy,” explains the operator.
The operator also asked residents to pre-cool their homes before 4 p.m. and then set their thermostats to 78 during setback hours and avoid recharging their electric vehicles.
Why this heat wave is different
High summer temperatures are the norm in California, but what makes this heat wave particularly dangerous is the length of time it is expected to linger in much of the state. In addition, there will be little lighting at night.
“Even after the sun sets, heat can pose a real danger, especially in large cities. Dark pavement and buildings are very effective at absorbing heat,” the Los Angeles weather bureau said.
And that’s why higher temperatures are more common in big cities, making them susceptible to an “urban heat island,” the agency explained.
The weather service defines a heat wave as a period of abnormally hot and humid weather lasting longer than two days.
Excessive heat has killed more people than any other extreme weather event in the US. According to data tracked by the National Weather Service, the number of deaths from heat has surpassed by more than 15-to-1 in the past decade.
Climate change is imposing conditions that have made extreme weather events more deadly and more common.
In Arizona, where temperatures are expected to hit triple digits this weekend, 111 people have died this year from heat-related complications in Maricopa County as of Wednesday, according to a report from the county’s public health department.
The report indicates that 38% of deaths occurred in people aged 50 to 64 and 80% of deaths occurred outdoors.
CNN’s Paradise Afshar, Taylor Romine and Alaa Elassar contributed to this report.