Extreme heat bakes West, toppling long-standing records

For many areas, the worst of the heat has yet to set in, particularly across California and the Desert Southwest, where Wednesday through Friday could be markedly hotter than what has already occurred.

Scattered wildfires have cropped up across California, Arizona, Utah and Montana, with fears that more may take advantage of the exceptional heat and bone-dry humidity. The ultra-warm temperatures are reinforcing a bitter drought that has wrought havoc across the greater region, simultaneously exacerbating concerns that autumn may bring a devastating fire season.

“This level of heat, and especially the duration of the heat, is dangerous to all population groups and steps should be taken to mitigate risk to heat exposure,” wrote the National Weather Service office in Las Vegas.

Excessive heat warnings blanket the West, where several days more of heat are likely before some relief arrives into the weekend. Here are some of the records that fell Tuesday:

• Salt Lake City hit 107 degrees, tying its hottest temperature ever recorded year-round and establishing a record for June.
• Denver made it to 101 degrees, breaking the daily record of 97 set in 1952 and 1993.
• Billings, Mont., made it to 108 degrees, tying the city’s hottest temperature recorded, on July 14, 2002.
• Laramie, Wyo., soared to 94 degrees, while Sheridan hit 107, both matching their highest temperatures on record.
• Casper, Wyo., hit 101 degrees, nabbing a new daily record by a whopping 8 degrees. It’s also its hottest temperature observed on record so early in the year.
• Death Valley, Calif., logged a high of 124.1 degrees, the highest temperature in the Lower 48 this year; Needles, Calif., made it to 121, setting a new daily record, and Palm Springs, Calif., to 120, topping its daily record by 4 degrees.
• Las Vegas snagged a high of 114 degree, falling just a bit short of the record of 116, seen in 1940.
• Phoenix hit 115 degrees, tying a daily record high set in 1974. A very diffuse, thin veil of smoke from the nearby Telegraph Fire probably reduced the temperature by a degree or two below what was originally forecast.

The heat to come

On Wednesday, high temperatures should settle back into the upper 80s or lower 90s across the northern Rockies, but the heat will consolidate and worsen over the southern Intermountain West and California, where widespread triple-digit heat is expected. Las Vegas is likely to hit 116, beating out the record of 114 degrees set in 1940. Phoenix could be equally hot, tying a record of 115 last observed in 1974.

Phoenix didn’t appear to make it below 91 degrees on Tuesday night, only the 10th time on record that has happened in June. Even though records date to 1933, five out of the other nine times have occurred since 2013 — attesting to the rapid pace of climbing overnight lows thanks to urbanization and human-caused climate change.

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Since the 1930s, summertime nightly lows in Phoenix have climbed by roughly nine degrees on average. Hot nighttime lows are frequently more dangerous than extreme daytime highs, as cooling shelters often close at night and, for elderly, vulnerable populations and those without cooling resources, the lack of relief offers no opportunity for the body to cool down.

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In California, extreme temperatures will exist just a few miles inland from the coast. At 6:30 p.m. Tuesday, the temperature in Malibu on Civic Center Way was 68 degrees, with a reading of 99 at Tapia Canyon.

The Central Valley will be the bull’s eye for heat, coming a day after widespread 100-degree readings. Lower 100s are likely Wednesday, followed by highs between 105 and 110 degrees Thursday and several readings topping 110 degrees Friday.

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A high of 110 degrees is expected in Sacramento on Thursday, which would beat the previous record by 7 degrees. Another record high of 107 is possible Thursday. The local Weather Service office advertised a “widespread high to very high heat risk.”

Bakersfield, Calif., is expecting three consecutive days near or at 110 degrees. That’s impressive but still a far cry from July 1908, when the city recorded 22 days in a row at or above 108. The Weather Service office in Hanford, Calif., referred to the forecast highs as “dangerously hot, life-threatening temperatures.”

Drought and wildfire concerns

Meanwhile, a spattering of wildfires has sparked up across California and the Southwest, including the 139,615-acre Telegraph Fire about 60 miles east of Phoenix, which was 59 percent contained as of Wednesday morning. A number of smaller spot fires have ignited along the Sierra Nevada foothills. Some of the smoke from the Arizona wildfires may reach New England on Friday, tinging sunsets with more vibrant shades.

The anomalous temperatures can be traced to an enormous “heat dome,” or a large area of high pressure languishing over the Four Corners region. That brings sinking air, clear skies and hot temperatures, simultaneously diverting clouds and other weather systems well to the north.

The frequency and intensity of higher-end heat domes has been linked to human-induced climate change; while triple-digit heat is a staple of summertime in the Desert Southwest, the heat is made more severe, and occurs more frequently, thanks to human influence.

“One of the biggest ways climate change is affecting us is by loading the weather dice against us. Extreme weather events occur naturally; but on a warmer planet many of these events are getting bigger, stronger, and more damaging,” Katharine Hayhoe, a climate scientist at Texas Tech University and the Nature Conservancy, said in an emailed statement. “They’re affecting our health, the safety of our homes, the economy, and more.”

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The heat is also amplified by antecedent dry conditions tied to an ongoing megadrought across the West, which brings lower relative humidity and makes it easier for the air to heat up. That, in turn, raises temperatures, leading to more evaporation and drying the ground further. That’s what atmospheric scientists refer to as a “feedback loop,” and it’s one that’ is difficult to break out of.

Nearly 55 percent of the West is experiencing an “extreme” or “exceptional” drought according to the U.S. Drought Monitor, and it’s likely that conditions will only worsen as the dry season continues.