It was 25°C at 4pm. By 10pm you're cold and wondering why you didn't bring a layer. This isn't unusual: on clear, dry evenings the temperature can drop several degrees per hour once the sun is gone.
Why the temperature falls after sunset
During the day, the sun pumps energy into the ground and air. After sunset, that input stops, but the ground keeps radiating heat outward into the atmosphere and eventually into space. This is called radiative cooling, and it happens continuously through the night.
Clouds act like a blanket. They absorb the outgoing radiation and radiate some of it back down toward the ground, slowing the cooling. On a clear night there's no such lid, and the temperature can fall fast.
| Conditions | Cooling rate |
|---|---|
| Clear sky, dry air, little wind | 2-4°C per hour |
| Partly cloudy | 1-2°C per hour |
| Fully overcast | 0.5-1°C per hour |
| High humidity or fog | Under 0.5°C per hour |
A day that peaks at 25°C can end up at 15°C by 11pm under a clear sky. The same day under thick cloud might still be 21°C at that hour.
When this catches people out
The classic scenario: a warm sunny afternoon, a barbecue or outdoor event that runs into the evening, and nobody brought anything extra because the forecast said 25°C. The forecast was right. The 25°C just left around 7pm.
Humidity makes a difference too. Damp air holds heat better than dry air, so humid summer evenings cool more slowly than dry spring evenings at the same afternoon temperature. A muggy night after a hot day often stays warmer than expected, while a beautiful clear spring day can leave you shivering by 8pm.
Can you wear shorts today?
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How KorteBroekAan.nl handles evening conditions
The site uses hourly weather data, so the clothing advice updates as the day progresses. If you're checking what to wear for a 9pm outdoor film screening, the site will give you the 9pm forecast rather than the afternoon peak. It's worth checking close to when you actually need the information, rather than once in the morning and then assuming it still applies.
The companion piece to this is why mornings feel colder than afternoons. For everything that feeds into the feels-like calculation at any hour, the Weather Explained section covers each factor separately.
Further reading
Related articles in the Weather Explained section: