July earned Phoenix hottest month on record for a US city

It's official: July in Phoenix was the hottest month ever recorded in a U.S. city, according to the Arizona State Climate Office at Arizona State University.

According to the National Weather Service in Phoenix, July wrapped up with an average temperature of 102.7 degrees Fahrenheit, beating the Phoenix area's previous record of 99.1 degrees, set back in August 2020. The record stands for as far back as records have been kept on Phoenix weather, which is 1895.

Last month set and broke heat record after heat record nearly every day since July 8. According to the weather service:

  • The average maximum temperature in July was 114.7 degrees.

  • The average minimum temperature was 90.8.

  • Every day in July had above-normal temperatures.

  • Only one day in July had a high temperature below 110 degrees.

  • July set a new all-time record for the most consecutive days with high temperatures at or above 110 degrees (31 days) from June 30 to July 30.

  • July had 19 days with low temperatures at 90 degrees or higher.

  • 17 days in July hit maximum temperatures at or above 115 degrees, breaking the previous record of six days set in 2020.

  • July set a new all-time record warm low temperature of 97 degrees.

  • Three days in July reached 119 degrees.

  • Twelve days in July broke or tied daily high temperature records.

  • Sixteen days in July broke or tied daily warm low temperature records.

  • The longest stretch of days under an excessive heat warning was set from July 1 to July 29, nearly quadrupling the number of days from the previous record, which was eight days.

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How did July manage to stay so hot for so long?

Usually, monsoon storms break hot streaks in July, but the weather pattern held Phoenix's monsoon to a late start this year, preventing the Valley from getting cloud cover or humidity at all, and thereby amplifying the prolonged heat, according to the weather service.

"We had a strong area of high pressure sitting right on top of Arizona for the majority of the month. It was unusually strong," said Mark O'Malley, meteorologist with the weather service in Phoenix. "Typically, that area of high pressure would move around, but it didn't this year, so we were stuck under the heat dome for the entire month."

Phoenix did not see its first monsoon thunderstorm until July 27, although the monsoon started nearly a month and a half before, on June 15.

Another monsoon storm hit the area again in the late evening of July 30. The following morning, humidity pushed low temperatures down to 83 degrees, the first below-normal temperature Phoenix recorded all month, and ultimately, the heat streak of 110-degree days broke apart later that day when the afternoon high temperature fell short by 2 degrees.

The lack of nighttime cooling also set this July stretch of hot days apart from others. In 1974, temperatures reached 110 degrees or higher for 18 consecutive days, setting the record that was broken last month. The average high in that period was about the same as this year. But the average low was 10 degrees cooler.

Scientists say the effects of climate change are evident this summer amid searing temperatures and other extreme weather conditions. With climate change pushing average temperatures higher, Arizona's heat waves have grown more intense.

In metro Phoenix, developed areas have grown significantly hotter than the surrounding desert. The city’s vast areas of exposed asphalt soak up the heat and release it at night, pushing temperatures higher, an effect known as the urban heat island.

O'Malley said hotter temperatures are likely to bounce back in the next few days, with high temperatures in the Phoenix area expected to reach 115 degrees again by this weekend.

"We want people to continue to use common sense for the rest of the summer. The afternoons will continue to be hot," O'Malley said. "Seek out shade and air conditioning and stay hydrated, as we're about to get hot again."

Hot weather tips

The Arizona Department of Health Services provided tips to prevent heat-related illness:

  • Drink water: It is recommended to drink at least 2 liters of water per day if people are staying inside all day. Those who spend time outdoors should drink 1 to 2 liters per hour they are outside.

  • Dress for the heat: Wear lightweight and light-colored clothing. Sunscreen should always be applied to exposed skin and it is recommended to wear a hat or use an umbrella when outdoors.

  • Eat small meals and eat more often: Experts recommend avoiding foods high in protein, which increase metabolic heat.

  • Monitor those at risk: Check on friends, family or others for signs of heat exhaustion or heat stroke.

  • Slow down and avoid strenuous activity: It is recommended to only do strenuous activity during the coolest hours of the day, between 4 a.m. and 7 a.m.

  • Stay indoors.

  • Take breaks when engaged in physical activity: Take a break in a cool place when doing an activity outside on a hot day.

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This article originally appeared on Arizona Republic: July earned Phoenix hottest month on record for a US city