(CNN) — Western states face another sweltering day in a record-breaking heat wave that has more than 24 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.

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 duration heat wave, at least five locations broke or tied their all-time record high temperatures. Guy said.

Las Vegas hit a high temperature Saturday of 117 degrees Fahrenheit. This tied their all-time record high on June 17.

Another concern is the record warm overnight temperatures.

Overnight low temperatures in portions of the Desert Southwest have failed to fall below 90 degrees. Death Valley reported a minimum of 107.7 degrees overnight — the warmest July temperature ever recorded on Earth — and has had a record number of consecutive nights over 100 degrees.

When overnight temperatures don’t cool enough it makes the human body 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 along with the 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 be impacted by the Bootleg Fire, a release from California ISO said.

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.

Transmission lines were tripped off on Friday and Saturday, California ISO said in the release, noting that it has limited “electricity flow from the Pacific Northwest to California and other states.”

Wildfires across the western US 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, 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 Jaime 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 Mt. Rainier, experienced approximately 30% of snowmelt between June 26-30, NWS Seattle meteorologist Jacob DeFlitch told CNN.

Another volcano in the state, Mt Baker also experienced “rapid snowmelt” DeFlitch said.

Pictures tweeted by the NWS Seattle show images of Mt. Rainier and Glacier Peak on June 18 which was before the heat wave — the volcanoes are covered with snow.

In contrast, the pictures taken of both volcanoes on July 10 from the NWS Seattle office rooftop it 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 snow pack,” 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.”

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