A summer marked by extreme, record-setting heat in the U.S. comes to a close

A summer marked by extreme and record-setting heat across much of the U.S. — particularly in Phoenix — has come to a close. Sunday’s autumnal equinox ushered in the fall season in the Northern Hemisphere.

Arizona, California, Florida, Maine and New Hampshire all experienced their warmest summers on record in 2024, according to the National Oceanic and Atmospheric Administration.

Cities and towns across the West and Southwest, in particular, set new heat records this year. Nearly 1 in 3 weather stations nationwide reported at least one record-high temperature over the summer.

A single weather station in Wyoming saw new record highs more than 30 times, according to an NBC News analysis of NOAA data.

NOAA gathers measurements from approximately 6,000 weather stations across the country. The data shows a flurry of new record highs in most parts of the U.S., save for a column in the middle of the country from Minnesota in the north to eastern Texas in the south.

This year, Phoenix endured its hottest summer in recorded history, surpassing a record set just last year, according to the National Weather Service, which maintains temperature data going back nearly 130 years.

The National Weather Service focuses on “meteorological summer”: the months of June, July and August. The classification differs from astronomical seasons but helps climatologists make more consistent comparisons between years based on annual temperature cycles.

The average temperature in Phoenix from June through August was 99 degrees Fahrenheit, two degrees hotter than the record set in 2023.

On Tuesday, Phoenix finally snapped a record streak of 113 consecutive days of temperatures at or above 100 degrees — around 3.5 straight months. The previous record of 76 consecutive days was set in 1993, according to the weather service.

In total, the city has endured 120 days at or above 100 degrees so far this year, inching closer to the record of 145 total days set in 2020.

Phoenix also set a record this year for the total number of days at or above 110 degrees, with 61 so far. The previous record of 55 days was set in 2023.

Last year, Phoenix sweltered through a record 31 straight days at or above 110 degrees, obliterating the previous record of 18 consecutive days set in 1974.

Over the last week, cooler weather has finally brought some relief to Arizona’s capital city. Phoenix last recorded a temperature at or above 110 degrees on Sept. 10. But the cooldown may be short-lived, as weather forecasts show that the city may see temperatures in the triple digits again next week.

Overall, the months of extreme temperatures are part of a worrying trend for the desert metropolis, which already has a reputation for unrelenting heat. Climate change is increasing the frequency, duration and intensity of heat waves, and Phoenix’s hottest five summers in recorded history have all been in the past 11 years, according to the National Weather Service.

The conditions have been deadly. Maricopa County, where Phoenix is located, has confirmed 256 heat-related deaths so far this year, with 393 more under investigation, according to county records. Last year, at least 645 people died from heat-related causes in Maricopa County, a 52% increase over the previous year.