Why does it feel colder than it is?
Because wind strips away the thin layer of warm air your body keeps around your skin, so you lose heat faster. The wind chill turns the temperature and the wind speed into one number: 30°F with a 15 mph wind feels like about 19°F.
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Your body wears a coat of warm air
Your skin warms the air touching it, and on a still day that thin layer stays put and insulates you a little. Wind keeps blowing it away and replacing it with fresh cold air, so your body has to keep heating new air. The faster the wind, the faster you lose heat, and the colder it feels.
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What the number means
The US National Weather Service's wind chill formula, in use since 2001, estimates how cold it feels on exposed skin for a person walking in the wind. It applies when it's 50°F or colder and the wind is at least 3 mph. It matters most for frostbite: once the wind chill drops below about −18°F, exposed skin can freeze in 30 minutes or less.
What wind chill doesn't do
Wind chill is about people and animals losing heat, not about objects. A car or a water pipe can't cool below the actual air temperature no matter how hard it blows, so pipes freeze at 32°F air, not 32°F wind chill. Wind just gets them there faster.
Damp air feels colder too: wet clothing and skin lose heat much faster than dry. Air Story shows the “feels like” temperature next to the real one on its first screen.
Questions people ask
- Is wind chill the same as the feels-like temperature?
- In cold, windy weather, yes: most apps show the wind chill as 'feels like'. In hot, humid weather they switch to the heat index instead.
- Can wind chill freeze water?
- No. Water freezes when the air itself is at or below 32°F. Wind only speeds up the cooling.