Southwest heatwave expected to see 100 days of temperatures over 100 degrees

Heatwave extends 100 degree F record by 100 days

Andrea Thompson

In Phoenix, Arizona, temperatures have soared to 100 degrees Fahrenheit (37.8 degrees Celsius) and often far exceeded it for the past 100 days. That trend will continue for at least a few more days in the city and many parts of the heat-stricken Southwest as another heat wave moves into the region, sending temperatures soaring.

The heat wave adds to a record-breaking summer in parts of the Southwest, including major cities like Phoenix and Las Vegas, which broke last year’s hottest summer weather records in those cities. “It’s unusual for that to happen two years in a row,” said Matt Salerno, a meteorologist with the National Weather Service’s (NWS) Phoenix office. “It’s quite a feat.” Even more surprising is that the city’s average temperature beat last year’s record by nearly 2 degrees Fahrenheit (1 degree Celsius), to 98.9 degrees Fahrenheit (37.2 degrees Celsius). “It’s just unbelievable, considering the average temperatures we’re living with here in Phoenix,” Salerno said.

Las Vegas “broke records by just about every measure,” said Matt Woods, a meteorologist with the NWS’s Las Vegas office. “It’s awful.”

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In both cities, this summer’s heat patterns have been a bit different than last summer. Last year, the Southwest started off with a mild June, followed by an unusually hot July, then cooled off again in late August when Hurricane Hillary hit. This summer hasn’t peaked like July 2023’s, but it’s been steadily scorching hot since the beginning. In Las Vegas, “we only had six days this summer where the high was below 100 degrees Fahrenheit,” Woods said. Meanwhile, Phoenix had a string of consecutive days above 100 degrees Fahrenheit, completely beating the city’s previous record of 76 days set in 1993.

Both summers’ record-breaking heat was the result of successive heat waves, when hot air was concentrated in one area for days. “That’s basically what we had for most of the summer,” Woods says. The clear skies that accompany these events mean “the surface gets hotter every day,” which in turn heats up the air just above the surface, Salerno says. These heat waves are becoming more frequent, lasting longer, and more intense, due to the extra heat trapped in greenhouse gases produced by burning fossil fuels.

This week’s heatwave will not be as intense or long-lasting as the one that hit the region in July, “but it is certainly unusual for this time of year,” Woods said. Residents are exposed to conditions that put them at risk for serious illness for longer. “Just because the temperatures are different than they were in July doesn’t mean they’re not dangerous,” Woods said. In the United States, extreme heat is more deadly than hurricanes, floods and tornadoes combined.

Those at higher risk for heat exhaustion, heat stroke, and other heat-related illnesses include young children, older adults, people with certain medical conditions or taking certain medications, people who work outdoors, and people who are homeless. Both Woods and Salerno stress that everyone should stay hydrated during a heatwave, avoid going outside during the hottest days of the day, and seek shade and air-conditioned areas whenever possible. Both scientists also warn that children and pets should never be left unattended in cars; 27 children left in cars have died from heat stroke so far this year.

“Essentially all heat deaths are preventable,” says Christy Aebi, an epidemiologist who specializes in heat-health risks. Many cities, including Phoenix, are looking at ways to warn residents more effectively and reduce deaths and hospitalizations from heat-related illnesses. The NWS is also working to improve its warning methods, including a new experimental tool called HeatRisk that shows places where the heat is severe enough to cause serious health problems.

While daytime heat is clearly a danger, Salerno and Woods stress that warm nights are an underestimated threat because they don’t give the body enough time to cool down. “Everyone wants to focus on the heat, but it’s actually the cold that’s the silent killer,” Woods says.

Phoenix’s average overnight low this summer was 87.5 degrees Fahrenheit (30.8 degrees Celsius), beating last summer’s low of 84.8 degrees Fahrenheit (29.3 degrees Celsius). There have been 37 days this season when the overnight low was at or above 90 degrees Fahrenheit (32.2 degrees Celsius), Salerno said. “The low in Phoenix is ​​the same as the high in most places,” he added.

And now, September is amplifying the danger and misery, with temperatures already beginning to be “much warmer than normal for this time of year,” Salerno said. Temperatures in Phoenix and the surrounding area could top 110 degrees Fahrenheit (43.3 degrees Celsius), and the event will likely surpass the 55 days last year that the city recorded temperatures above 110 degrees.

The heat could continue into next week. The last day last year in Phoenix that exceeded 110 degrees was Sept. 10, 2023. (The latest day the city reached 110 degrees in a single year was Sept. 19, 2010.) “Hopefully this is the last time we’ve had 110-degree heat,” Salerno said, sounding exhausted.