Weather · Phoenix · 1896–2026
Phoenix After Dark
For most of the last century, a Phoenix night that stayed at 90°F or warmer almost never happened. Now it happens every summer. In 2024 it happened 39 times.
Every summer night since 1896
Each row below is one summer, June through September. Each sliver is one night, colored by how low the temperature fell. Read it from the top down: for most of a century, nearly every night cooled below 90°F. Then orange starts creeping in, and the bottom rows fill up.
How low did it get? Every summer night in Phoenix
The day's lowest temperature, June 1 to September 30. Hover or tap a night for the reading.
Source: NOAA, official Phoenix record (downtown until 1933, Sky Harbor Airport since). Blank slivers are missing readings.
From almost never to every year
Counted up, the change is hard to miss. From 1950 to 1979, Phoenix averaged 0.2 nights a year that stayed at 90°F or warmer. Over the last 30 years (1996–2025) it averaged 11.1. That jump is far bigger than the normal swing from one summer to the next: the for the difference runs from 7.8 to 14.4 nights a year.
The record keeps falling too. 2023 set it with 35 nights, then 2024 broke it with 39. Those counts match what the National Weather Service in Phoenix reported.
Nights per year that stayed at 90°F or warmer
Phoenix, 1896–2026. Hover a year for its count.
Show the numbers by year
| Year | Nights at 90°F+ | Nights at 85–90°F |
|---|
Days got hotter. Nights got hotter faster.
Phoenix summer afternoons have warmed too. The average June-to-August high went from 101.8°F in the 1950s to 107.8°F in the 2020s, up 6.0°F. But the average low rose from 75.5°F to 84.9°F, up 9.4°F. The nights are where Phoenix has changed most.
Change in the average summer temperature since the 1950s
June–August average, by decade, compared with the 1950s (°F). The 2020s so far include 7 summers.
The record book only moves one way
Every calendar date has a record high and a record low. When a day beats one, the record book changes. Since 1991, Phoenix has set 279 new daily record highs. It hasn't set a single new daily record low since December 23, 1990.
New daily records set in Phoenix, by decade
Counted from the start of the official record in 1895. Hover a bar for the count.
Why the nights changed
Two things are happening at once. The planet is warming, and Phoenix has grown around its thermometer. Sky Harbor Airport sits at the center of a metro area that has spread across what used to be farmland and desert. Pavement, roofs and walls soak up heat all day and give it back all night. That is the , and it shows up most clearly after dark.
Researchers at Arizona State University have found that heat from the growing west and northwest Valley drifts into central Phoenix overnight, keeping Sky Harbor warm (ABC15). This story shows what the official thermometer recorded. It doesn't measure how much of the change comes from each cause.
For people in Phoenix, the cause matters less than the result. The hours that used to bring relief now often don't.
How this was measured
- Data: the official Phoenix daily record kept by the National Weather Service (NOAA's "Phoenix Area" record, via the Regional Climate Centers' ACIS service). It begins in 1895 downtown and continues at Sky Harbor Airport from June 1933. 1896 is the first full year.
- A 90° night is a calendar day whose lowest temperature was 90°F or higher. The low usually comes just before sunrise.
- Checked against the National Weather Service: 2024: 39 nights (NWS Phoenix, 2024 in review); 2023: 35, the previous record; and the all-time warmest low of 97°F, first set July 19, 2023 and tied July 24, 2026.
- The comparison of 1950–1979 with 1996–2025 uses complete years only. The 95% range comes from resampling the years 20,000 times.
- Daily records are counted as each one is set, from the start of the record. Early decades naturally set more of both kinds; the change shows in how highs and lows compare within each decade.
- Missing data: every summer since 1896 has at least 95% of its nightly readings.