More than 40 million Americans are in the crosshairs of triple-digit heat this week, with some spots soaring over 120 degrees as records fall across the West. The heat in many areas is dangerous, prompting excessive-heat warnings in seven states where temperatures will be hazardous to human health.

The heat also reinforces a devastating drought that continues to reshape the landscape of the West while bolstering worries of what lurks ahead in the fall come fire season. More than half of the western United States is gripped by “extreme” or “exceptional” drought, according to the U.S. Drought Monitor, the two most severe categories.

In the longer-range, odds continue to favor prolonged hot and dry weather, though some modest relief may arrive this weekend.

But several days of unrelenting, record-threatening heat is predicted to take a toll. Heat is the leading weather-related killer in the United States, so National Weather Service offices are urging preparedness.

“Extreme temperatures such as these can extract a heavy cost, from an economic and health perspective,” tweeted the Weather Service office in Phoenix, where numerous heat records are predicted to fall.

In Texas, where the heat isn’t as extreme but temperatures are still above normal, the state’s power grid manager, ERCOT, on Monday asked residents to conserve power through the week.

On Monday, records were shattered in the desert Southwest and the Rockies, including in Tucson, where highs hit 112 degrees. Las Vegas spiked to 110.

“Temperatures in Las Vegas will reach at least 113 degrees [on Tuesday], and highs are forecast to be at or above 113 degrees through Saturday,” wrote the Weather Service office in Las Vegas. “A five-day stretch of max temperatures at or above 113 has only occurred five times in Las Vegas for the period of record dating back to 1937.”

The last time such a five-day stretch occurred was in 2017.

The city could also come close Wednesday to tying or breaking its record high temperature of 117 degrees. State records are also in jeopardy in Nevada and Arizona. The highest temperatures ever recorded there are 125 and 128 degrees respectively, both set on June 29, 1994.

Highs in Phoenix reached 112 degrees on Monday and didn’t fall below 90 until after 3 a.m. They’re slated to crest at 116 or 117 degrees on Tuesday, Wednesday, Thursday and Friday before “only” hitting 114 degrees on Saturday. That would set a record every day through Friday.

In fact, Phoenix has only once before seen a four-day stretch of highs at or above 116 degrees; this would be only the second time on record dating back to 1933. Wildfire smoke may bring a hazy look to the sky as it drifts in from the 104,755 acre Telegraph fire about 60 miles east of the city. It was 68 percent contained as of Tuesday morning. Smoke from the wildfires could reach New England by Friday as it surfs the jet stream east.

In addition, ground-level ozone and the concentrations of other pollutants have spurred the issuance of an air quality alert for the greater Phoenix area. The Arizona Department of Environmental Quality is warning of an “increase in adverse health effects.”

Los Angeles should join the triple-digit club as well, hitting 100 degrees on Tuesday before settling into the mid-90s on Wednesday.

Death Valley, Calif., famous for holding the highest temperature ever observed on the planet, is expected to hit 125 degrees for the remaining days this week. It hit 118 degrees Monday, the nation’s hottest temperature. Wednesday and Thursday could feature highs of 127 degrees, near its June record. Overnight “lows,” or more realistically “minimum temperatures,” will hover around 97.

In California’s Central Valley, most places will hit 90 degrees on Tuesday, but the real heat starts Wednesday — widespread temperatures between 100 and 105 will be the story for places like Redding, Sacramento and Fresno, where excessive-heat warnings are in effect. On Thursday, highs could flirt with 110 degrees, with temperatures approaching 110 on Friday and Saturday. Sacramento could establish a record Thursday by as much as 7 degrees.

It’s not just the desert Southwest and California’s inland valleys that are baking. Extreme heat has surged through the Rockies and Intermountain West, reaching as far north as Saskatchewan and Alberta, Canada.

Billings, Mont., is forecast to hit its highest temperature ever recorded on Tuesday — an astonishing 109 degrees. The city has only reached 108 degrees once before on July 14, 2002.

“PLEASE stay safe from the heat today and be careful not to spark a fire!” wrote the Billings Weather Service office.

Nearby Helena hit 104 degrees, setting a June record. The average high for the date is 74 degrees.

Casper, Wyo., is aiming for 102 degrees Tuesday. Salt Lake City, which hit 102 degrees on Saturday and spiked to 103 on Monday, could come close to tying or breaking the June record of 105 degrees as the mercury continues to soar on Tuesday.

Monday’s high was also the earliest 103-degree reading on record in the Utah capital, where most years don’t see temperatures so high.

The heat should relent some later in the week across the northern Rockies, but will continue in full force across the Southwest.

Meanwhile, the temperatures are sparking serious wildfire concerns, the heat drying out the ground and providing a breeding ground for speedy fire growth. A number of small brushfires and wildfires have cropped up in Southern California due to offshore winds, extreme temperatures and low relative humidity. The worst fire weather there is expected Wednesday.

Red-flag warnings for high fire danger blanket much of the western United States.

“The low levels will remain fairly dry and thunderstorms will produce little in the way of precipitation, which also increases the concern for producing new fire starts,” cautioned the Weather Service in Las Vegas. Atmospheric profiles will also favor erratic winds with any dry thunderstorm that develops.

In the more-distant future, the ongoing heat will exacerbate fire risk across the West this autumn, since the hot temperatures lead to more evaporation and sap the ground and vegetation of moisture. That drop-off in humidity also makes it easier to achieve higher temperatures, which in turn reinforce the drought. It’s a cycle that is difficult to break out of that has already brought extreme or exceptional drought to nearly 55 percent of the region. Desperate public officials in Utah have been leading prayers for rainfall.

Lake Mead, the nation’s largest reservoir located in Nevada and Arizona, dipped to its lowest level on record last week and is projected to fall further due to the heat-drought double-whammy.

The frequency and intensity of heat events, tied to sprawling areas of high pressure colloquially known as heat domes, have been linked to human-induced climate change. While events like this aren’t caused by climate change, they are intensified by it, their magnitudes becoming markedly more severe.