April, after a long cold winter. It hits 15°C and people are out in t-shirts, sitting on terraces, looking at each other with relief. September, after a warm summer. 15°C and everyone's back in jackets, saying it's getting cold. Neither group is wrong. The temperature is the same. Almost everything else is different.
The objective part: conditions vary a lot at 15°C
The same air temperature can produce a wide range of feels-like temperatures depending on wind, sun, and cloud cover. A still, sunny 15°C day with no wind can feel close to 20 to 22°C. The same 15°C with 35 km/h wind and thick cloud can feel like 9°C.
| Conditions | Air temperature | Feels-like |
|---|---|---|
| Sunny, no wind | 15°C | ~20-22°C |
| Sunny, 25 km/h wind | 15°C | ~12°C |
| Overcast, no wind | 15°C | ~14°C |
| Overcast, 35 km/h wind | 15°C | ~9°C |
| Rain, 20 km/h wind | 15°C | ~10°C |
That's a 13-degree spread in felt temperature, all at 15°C. So when people disagree about whether 15°C is warm or cold, they're often not comparing the same conditions.
The subjective part: acclimatisation is real
Your body adjusts to the temperature range it's been experiencing. After months of sub-10°C weather, 15°C genuinely does feel warm because your baseline has shifted. Your thermoregulation adapts, your clothing habits have adjusted toward heavier layers, and the contrast is noticeable. By September you've been operating in 20-28°C for months, and 15°C represents a significant step down from that. The temperature is identical. The context is not.
This isn't a psychological trick or a matter of attitude. Thermal acclimatisation is a documented physiological process. Your body actually processes temperature differently depending on what it's been used to.
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How KorteBroekAan.nl handles it
The site calculates feels-like temperature for whatever the current conditions are, which handles the objective part. For the subjective part, the Weakling to Legend slider lets you shift the threshold for clothing recommendations to match your own tolerance. If you run cold and 15°C on a sunny day still feels chilly to you, moving toward the Weakling end adjusts the advice. If you've been doing cold-water swimming all winter and think 15°C is basically summer, the Legend setting is there.
Related reading: why 20 degrees is not always shorts weather explores the same variability at a temperature most people assume is straightforwardly warm. The full Weather Explained section covers all the factors that contribute to the spread.
Further reading
Related articles in the Weather Explained section:
Read next
Why 20 degrees is not always shorts weather
20°C sounds like it should be comfortable. And often it is. But add enough wind or cloud cover and it stops feeling that way fairly quickly.
Why weather apps sometimes feel different from outside
The app said 18°C and pleasant. You're outside in five minutes and you're cold. Or the reverse. Here's why that gap exists and what to do about it.
Why direct sunlight feels warmer
15°C in full sun, no wind, a sheltered bench. It feels genuinely pleasant. Here's the physics of why solar radiation adds warmth the thermometer doesn't measure.
Why drizzle feels different from a rain shower
Drizzle looks harmless and often is, until it isn't. The difference between fine rain and heavy showers goes beyond wetness rates.
Can I wear shorts at 15 degrees?
15°C is right at the tipping point. Whether you can wear shorts at that temperature depends on wind, sun and how your body has adapted to the season.