Phoenix hits at least 110 for 19th straight day, breaking U.S. city records in worldwide heat wave

As human-caused climate change and a newly formed El Nino are combining to shatter heat records worldwide, the Phoenix region stands apart among major metropolitan areas in the U.S.

No other major city – defined as the 25 most populous in the United States – has had any streak of 110-degree days or 90-degree nights longer than Phoenix, said weather historian Christopher Burt of the Weather Company.

National Oceanic and Atmospheric Administration climate data scientists Russ Vose and Ken Kunkel found no large cities with that streak of warming, but smaller places such as Death Valley and Needles, California; and Casa Grande, Arizona, have had longer streaks. Death Valley has had an 84-day streak of 110-degree temperatures and a 47-day streak of nighttime temperatures that haven't fallen below 90, Vose said.

For Phoenix, it’s not only the brutal daytime highs that are deadly. The lack of a nighttime cooldown can rob people without access to air conditioning of the break from the heat that their bodies need to continue to function properly.

With Tuesday’s low of 94, the city has had nine straight days of temperatures that didn’t go below 90 at night, breaking another record there, according to National Weather Service meteorologist Matt Salerno, who called it “pretty miserable when you don’t have any recovery overnight.”

On Monday, the city set a record for the hottest overnight low temperature: 95 (35 degrees Celsius).

Some 200 cooling and hydration centers have been set up across the metro area to cool residents, both most shut down at between 4 p.m. and 7 p.m. due to staffing and funding issues.

“Long-term exposure to heat is more difficult to withstand than single hot days, especially if it is not cooling off at night enough to sleep well,” said Katharine Jacobs, director of the Center for Climate Adaptation Science and Solutions at the University of Arizona.

The last time Phoenix didn’t reach 110 F (43.3 C) was June 29, when it hit 108 (42.2 C). The record of 18 days above 110 that was tied Monday was first set in 1974, and it appeared destined to be shattered with temperatures forecast above that through the end of the week.

“This will likely be one of the most notable periods in our health record in terms of deaths and illness,” said David Hondula, chief heat officer for the City of Phoenix. “Our goal is for that not to be the case.”

Phoenix’s heat wave has both long and short-term causes, said Arizona State University’s Randy Cerveny, who coordinates weather record verification for the World Meteorological Organization.

“The long-term is the continuation of increasing temperatures in recent decades due to human influence on climate, while the short-term cause is the persistence over the last few weeks of a very strong upper level ridge of high pressure over the western United States,” he said.

That high pressure, also known as a heat dome, has been around the Southwest cooking it for weeks, and when it moved it, moved to be even more centered on Phoenix than ever, said National Weather Service meteorologist Isaac Smith.

The Southwest high pressure not only brings the heat, it prevents cooling rain and clouds from bringing relief, Smith said. Normally, the Southwest’s monsoon season kicks in around June 15 with rain and clouds. But Phoenix has not had measurable rain since mid-March.

“Although it is always hot in the summer in Phoenix, this heat wave is intense and unrelenting,” said Jacobs. “Unfortunately, it is a harbinger of things to come given that the most reliable projected impacts of climate change are those that are directly related to the increase in global temperatures.”