18°C on a sunny day versus 18°C under a solid grey sky. The thermometer says the same thing. Your skin does not agree. Cloud cover is one of the most straightforward factors in how temperature actually feels, yet most weather apps reduce it to an icon and move on.
What clouds do to solar radiation
A fully overcast sky blocks 70 to 80 percent of direct solar radiation before it reaches the ground. On a clear day that radiation hits your skin directly and adds 4 to 8 degrees of perceived warmth above the air temperature. In summer the effect can be even larger. On a completely cloudy day, almost none of that reaches you, and the air temperature is basically what you get.
| Conditions | Air temp | Cloud cover | Feels-like |
|---|---|---|---|
| Sunny morning, little wind | 16°C | Clear | ~21°C |
| Grey day, little wind | 16°C | Fully overcast | ~15°C |
| Mixed cloud | 18°C | Partly cloudy | ~18-20°C |
| Sunny but windy | 18°C | Clear | ~15-17°C |
The last row is worth noting. Sun adds warmth, but wind takes it back. A bright breezy day can end up feeling cooler than a still, overcast one.
Why partly cloudy is the awkward case
Broken cloud cover is genuinely difficult. When the sun is out you feel fine; the moment it ducks behind a cloud the temperature seems to drop several degrees. You're not imagining it. The radiation switch is essentially on or off, and that creates a 5 to 6 degree swing in perceived warmth depending on whether you happened to check in a sunny or cloudy moment. This is one reason weather advice based on a single point-in-time temperature reading can feel unreliable on mixed days.
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How KorteBroekAan.nl handles cloud cover
Cloud cover percentage is part of the feels-like calculation on the site. A clear forecast raises the perceived warmth above the raw air temperature; heavy overcast brings it back down toward the thermometer reading. The clothing recommendation adjusts accordingly rather than treating all 18°C days as equivalent.
Cloud cover works together with wind, humidity, and sun angle to produce the number you actually experience. The other articles in the Weather Explained section go through each of those factors in more detail.
Further reading
Related articles in the Weather Explained section: