By Madeline Holcombe and Joe Sutton, CNN
Western states face another sweltering day in a record-breaking heat wave that has more than 18 million people under heat alerts.
The heat will extend over southeast Oregon, northern California, the Mojave Desert, eastern California, and parts of Nevada and Utah, according to CNN meteorologist Michael Guy.
The ridge of high pressure is expected to level out, bringing more typical temperatures back to the area, with alerts beginning to expire Monday and some lasting to Tuesday evening.
The cooling will be a welcome relief to an area that has been baking under dangerous temperatures.
Andrew Phelps, Oregon Office of Emergency Management director, said the drastic changes in weather “are things none of us have experienced and have no muscle memory to rely on.”
“We’re experiencing historic flooding in places that didn’t used to flood, fire in places that didn’t use to burn,” Phelps said.
Oregon’s medical examiner confirmed 83 heatwave deaths as of July 9 and said 32 other deaths are being investigated. The state’s hospital surveillance database showed more than 800 heat-related illness visits between June 24 and July 4.
In California, wildfires have burned more than three times as much land so far this year than in 2020, when the state went on to record its worst fire season ever. There have been 4,991 fires in California since January, mostly due to extremely hot and dry conditions, according to a tweet from the California Department of Forestry and Fire Protection (Cal Fire).
By this time last year, roughly 700 fewer fires had burned across the state.
More than 103,000 more acres have burned this year through July 11 than in 2020, according to updated data from Cal Fire on Monday.
Earlier this month, temperatures reached 15 to 30 degrees above normal, Guy said. Much of the West is expected to remain 5 to 10 degrees above average, he added. During this part of the long duration heat wave, at least seven locations broke or tied their all-time record high temperatures. Guy said.
Las Vegas hit a high temperature Saturday of 117 degrees Fahrenheit. This was the fifth time the city reached this all-time record temperature since July 24, 1942.
Another concern is the record overnight temperatures.
Overnight low temperatures in portions of the Desert Southwest have failed to fall below 90 degrees. When it doesn’t get cool enough overnight, the human body is more susceptible to the effects of heat stress, putting people at greater risk of heat stroke and death, Guy said.
55 large fires burning
In California and Nevada, residents are being asked to conserve energy in response to heat and wildfires.
In a tweet posted Sunday afternoon, NV Energy said the extreme heat and out-of-state wildfires are impacting the transmission lines in the region, which is affecting the energy supply.
“Thank you for conserving energy today between 6 p.m. and 9 p.m. to help reduce the strain on the electric grid,” the tweet said.
Electrical transmission lines from southern Oregon to California are still being impacted by the Bootleg Fire, a news release from the California Independent System Operator (California ISO) said. The fast-moving fire, which started on July 6, isn’t expected to be contained until November 30.
The Bootleg fire has destroyed seven structures and threatens 1,926 more, according to Bootleg fire public information officer Brad Bramlett.
The fire grew more than 100,000 acres over the weekend, with more than 150,800 acres burned as of Monday morning, according to Inciweb.
Bramlett told CNN the 1,027 firefighters on the scene are mostly hand crews using rakes and tools along the exterior of the blaze to create a fire break.
Transmission lines were tripped off on Friday and Saturday, California ISO said, noting that it has limited “electricity flow from the Pacific Northwest to California and other states.”
Wildfires across the western United States have been growing, fueled by the hot, dry weather.
More than 11,300 wildland firefighters are battling the ongoing fires, the National Interagency Fire Center (NIFC) said.
Across 12 states, 55 large fires have burned 768,307 acres, according to the NIFC.
In California, the largest fire currently burning is the Beckwourth Complex Fire in the area of the Plumas National Forest.
“The Beckwourth Complex (contains two fires) is California’s largest current fire,” Beckwourth Complex Fire information spokesman Mike Ferris told CNN. “There have been 3,061 people affected by the evacuation with 1,199 residences threatened.”
And the River Fire in the state has exploded in the vicinity of a route that leads to Yosemite National Park, Cal Fire spokesperson Jamie Williams told CNN.
Fire officials have received calls from “quite a few visitors and many phone calls from residents” regarding the smoke and fire information, Williams said.
Rapid snowmelt on volcanoes
During the historic heat wave, some of Washington state volcanoes experienced “significant” snowmelt in June, according to a meteorologist at the National Weather Service (NWS) Seattle office.
Paradise, which is located at 5,400 feet on Mount Rainier, experienced approximately 30% of 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.
Pictures tweeted by the NWS Seattle show Mt. Rainier and Glacier Peak on June 18, before the heat wave, both covered with snow.
In contrast, pictures taken of both volcanoes July 10 from the NWS Seattle office rooftop reveals much less snowpack on the peaks.
“From a visual standpoint, it shows a very significant change in such a short time period for the mountains’ snowpack,” DeFlitch said.
Glacier Peak has an elevation of 10,541 feet, and is located in Snohomish County, north of Seattle.
DeFlitch said it is common to see snowmelt during the summer at the volcanoes, but “this is a large amount for such a short period of time.”
“The significance of the snowmelt is the magnitude and duration of the heat from the West, particularly Pacific Northwest, has experienced from late spring into early summer,” Guy said.
“In this instance, the magnitude of the heat was so strong that it was able to warm temperatures at a height that normally never gets warm and melt the snow,” he added. “This is very significant when talking about climate change and feedback loops that only exacerbate the problem to worsen, and in my perspective very concerning.”
Correction: An earlier version of this story overstated the number of people affected by heat alerts. More than 18 million people remain under heat alerts. The story also incorrectly described the heat record date in Las Vegas. It is the fifth time the city reached this all-time record temperature since July 24, 1942.
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CNN’s Hollie Silverman, Stella Chan and Kay Jones contributed to this report.