The heat will spread over southeastern Oregon, northern California, the Mojave Desert, eastern California and parts of Nevada and Utah, according to CNN meteorologist Michael Guy .
The high pressure ridge is expected to stabilize, bringing back more typical temperatures to the region, with alerts starting to expire on Monday and some continuing until Tuesday evening.
Cooling will be a welcome relief in an area that has cooked to dangerous temperatures.
Earlier this month, temperatures reached 15 to 30 degrees warmer than normal, Guy said. Much of the west is expected to remain 5 to 10 degrees warmer than average, he added. During this part of the long-lasting heat wave, at least seven locations broke or equaled their all-time highs. Guy said.
Las Vegas hit a high temperature of 117 degrees Fahrenheit on Saturday. It was the fifth time that the city had reached this temperature record since July 24, 1942.
Another concern is the record high temperatures during the night.
Low nighttime temperatures in parts of the southwest desert did not drop below 90 degrees. When nighttime temperatures don’t cool enough, the human body is more susceptible to the effects of heat stress, putting people at increased risk of heat stroke and death, Guy said.
55 big fires burning
In California and Nevada, residents are urged to conserve energy in response to heat and wildfires.
“Thank you for conserving energy today between 6pm and 9pm to help relieve pressure on the power grid,” the tweet said.
Transmission lines were tripped on Friday and Saturday, California’s ISO said in the statement, noting that it has restricted “the flow of electricity from the Pacific Northwest to California and other states.”
Wildfires in the western United States have escalated, fueled by the hot, dry weather.
More than 11,300 wildland firefighters are battling ongoing fires, the National Interagency Fire Center (NIFC) said.
In 12 states, 55 large fires burned 768,307, according to the NIFC.
In California, the largest fire currently burning is the Beckwourth Complex Fire in the Plumas National Forest region.
“The Beckwourth Complex (contains two fires) is the largest current fire in California,” Beckwourth Complex Fire Information spokesperson Mike Ferris told CNN. “There were 3,061 people affected by the evacuation and 1,199 residences at risk.”
And the River Fire in the state exploded near a road leading to Yosemite National Park, Cal Fire spokesman Jamie Williams told CNN.
Firefighters have received calls from “quite a few visitors and numerous phone calls from residents” regarding information about the smoke and the fires, Williams said.
Rapid snowmelt on volcanoes
During the historic heat wave, some volcanoes in Washington state experienced “significant” snowmelt in June, according to a meteorologist with the Seattle office of the National Weather Service (NWS).
Paradise, located 5,400 feet on Mount Rainier, experienced about 30% snowmelt between June 26 and 30, NWS Seattle meteorologist Jacob DeFlitch told CNN.
Another volcano in the state, Mount Baker, also experienced “rapid snowmelt,” DeFlitch said.
In contrast, photos taken of the two volcanoes on July 10 from the roof of the NWS office in Seattle reveal much less snow accumulated on the peaks.
“From a visual point of view, this shows a very big change in such a short time for the snowpack of the mountains,” said DeFlitch.
Glacier Peak has an elevation of 10,541 feet and is located in Snohomish County, north of Seattle.
DeFlitch said it’s common to see snow melt on volcanoes during the summer, but “it’s a large amount for such a short period of time.”
“The significance of the snowmelt is the magnitude and duration of the western heat, especially the Pacific Northwest, experienced from late spring to early summer,” Guy said. .
“In this case, the amplitude of the heat was so great that it was able to warm the temperatures to a height that normally never warms up and melt the snow,” he added. “This is very important when we talk about climate change and feedback loops that only exacerbate the problem and get worse, and in my opinion very concerning.”
Correction: An earlier version of this story overestimated the number of people affected by heat alerts. More than 18 million people remain on heat alert. History has also incorrectly described the date of the heat record in Las Vegas. This is the fifth time that the city has reached this temperature record since July 24, 1942.
CNN’s Hollie Silverman, Stella Chan and Kay Jones contributed to this report.
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