Chapter 3 of 6
The days aren't the whole story. The nights are.
Warm nights (never below 75°F) went from 1.2 a year in the 1940s to 6.8 in the 2010s, the fastest-moving number in this entire record. A hot day is uncomfortable. A hot night that never lets a body recover is the one that matters physiologically, especially for older or medically vulnerable people.
Warm nights per year, by decade
Nights that never drop below 75°F. This is the number that keeps climbing, even in a decade like the 2020s, where daytime heat hasn't kept pace.
Summer nights, getting warmer
Mean overnight low, June through August, every year since 1940.
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The hottest nights, in context
Ten record-setting overnight lows on the left. Every June-through-August night since 1940 on the right, colored by low temperature, to show whether hot nights cluster in a particular stretch of summer or a particular era.
- 82°F low on 2011-08-04
- 81°F low on 2007-08-17
- 80°F low on 1980-07-11
- 79°F low on 2007-08-11
- 79°F low on 1983-07-24
- 79°F low on 2007-08-08
- 79°F low on 1954-08-17
- 79°F low on 1954-08-06
- 79°F low on 1944-06-24
- 79°F low on 1993-07-29
Why nights lag days in the data but lead them in the trend: elevation and distance from the Gulf keep Atlanta's daytime humidity, and its "feels like" premium, comparatively low (see Chapter 2). But urban heat retention overnight is a different mechanism: pavement and buildings that absorbed heat all day release it slowly after dark, regardless of how humid the afternoon was. See About for how this data was pulled.