PHOENIX — Phoenix summers are known for brutal heat, but the nights are no longer offering much relief — and the data shows this year is among the worst on record for overnight lows.
Since June 1, overnight lows in the Valley are averaging 84.5 degrees. There have been 14 nights that stayed below 80 degrees, 8 that climbed above 90, and 1 that exceeded 95.
This summer ranks fifth hottest on record for overnight lows. The highest average summer low ever recorded was in 2024, at 87.5 degrees. Every one of the top five hottest summers for overnight lows has happened this decade.
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Year to date, Phoenix is living through the warmest average overnight temperature on record — 68 degrees. That is 3 full degrees warmer than the second-warmest year on record, 2015.
The five hottest overnight lows ever recorded in Phoenix are:
97 degrees — recorded twice, once on the 24th and once on July 19, 2023
96 degrees — July 15, 2003
96 degrees — July 22, 2023
95 degrees — Aug. 12, 2003
The long-term trend makes the pattern clear: Overnight lows are climbing. In 1982, the three-year average summer low was 81 degrees. Twenty years later, it had risen to 82.9 degrees. It has climbed another 3 degrees since then.
The trend extends beyond the Valley. Flagstaff's three-year summer average overnight low has risen from 48.7 degrees in 1982 to 50.9 degrees today.
Statewide, data from over 31 airport weather stations tells a similar story. One station — Prescott — is posting its warmest average July lows this year. 84% of the remaining stations recorded their warmest July overnight temperatures between 2020 and 2025.
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