A wind chill factor is a number that tells you how cold the air feels on exposed skin once wind is added to the actual temperature. The National Weather Service calculates it from air temperature and wind speed, and it only applies at 50 degrees Fahrenheit or colder with wind above 3 mph.
Why moving air pulls heat off your skin
Your body warms a thin layer of air right next to your skin. On a still day that layer stays put and acts like a light blanket. Wind keeps stripping it away and replacing it with fresh cold air, so your skin loses heat faster than the thermometer reading alone would suggest.
The wind chill figure translates that faster heat loss into a temperature you can relate to. When the forecast says 10 degrees with a wind chill of minus 9, it means your face will lose heat about as fast as it would on a calm day at minus 9.
Reading numbers off the wind chill chart
These pairs come from the National Weather Service wind chill chart.
| Air temperature | Wind speed | Wind chill |
|---|---|---|
| 40°F | 10 mph | 34°F |
| 30°F | 15 mph | 19°F |
| 20°F | 20 mph | 4°F |
| 10°F | 25 mph | minus 11°F |
| 0°F | 15 mph | minus 19°F |
| minus 10°F | 30 mph | minus 39°F |
The chart is also shaded to show frostbite risk, with bands for exposed skin freezing in 30 minutes, 10 minutes and 5 minutes. The weather service uses 0 degrees with a 15 mph wind as its example, a wind chill of minus 19 where exposed skin can freeze in 30 minutes. Notice how quickly the numbers drop once wind picks up; the first few miles per hour do the most damage.
To use the full chart, find the air temperature along the top and the wind speed down the side, then read across to where the two meet. Weather apps do this math for you, but the chart helps when you’re planning a morning run or a long wait outdoors and the forecast calls for wind to rise later in the day.
Where the wind chill formula came from
The current index took effect on November 1, 2001. It was developed by a joint group that included the National Weather Service, its Canadian counterpart and university researchers, and it uses heat transfer theory based on how the body loses heat on cold, windy days.
One detail explains why wind chill can feel slightly off. Official wind readings come from instruments mounted 33 feet up, where wind blows harder. The formula adjusts that down to about 5 feet, the typical height of an adult’s face. For anyone who likes math, the weather service’s formula is 35.74 + 0.6215T minus 35.75V0.16 + 0.4275TV0.16, with T in Fahrenheit and V in miles per hour.
Wind chill and your car, pipes and pets
Wind chill describes people, and to a degree animals with exposed skin. It doesn’t push objects below the real temperature. The weather service says the only effect on things like car radiators and water pipes is that they cool to the air temperature more quickly. A pipe won’t freeze at 35 degrees just because the wind chill reads 27.
So when you’re deciding whether to drip faucets or add antifreeze, go by the actual air temperature. When you’re deciding how long a walk or a bus stop wait can last, go by the wind chill.
How the forecast warns you now
In October 2024 the National Weather Service renamed its wind chill alerts to make clear that cold can be dangerous with or without wind. Wind Chill Warnings became Extreme Cold Warnings, Wind Chill Watches became Extreme Cold Watches, and Wind Chill Advisories became Cold Weather Advisories. Thresholds differ by region, so check your local weather service office for what triggers each alert where you live.
On those days, cover the skin that faces the wind first: ears, nose, cheeks and fingers. Several thin layers under a windproof outer shell hold warmth better than one bulky coat that lets air through, and mittens keep fingers together so they share heat. If skin stays numb or looks discolored after you warm up, contact a doctor.
Frequently asked questions
Is wind chill the same as the feels like temperature?
In winter they're usually the same idea. Many weather apps show a feels like number that uses wind chill when it's cold and the heat index when it's hot. Wind chill specifically applies at 50 degrees Fahrenheit or colder with wind faster than 3 mph.
Can wind chill freeze water when the temperature is above 32 degrees?
No. The National Weather Service says wind only makes objects cool to the actual air temperature faster. Water, pipes and car engines can't drop below the real temperature because of wind, so freezing still requires the air itself to reach freezing.
Does wind chill affect dogs and cats?
Wind speeds up heat loss from exposed skin on animals too, especially on ears, noses and paws, and on short coated breeds. Use the wind chill as a guide for shortening walks and outdoor time, and ask your veterinarian about cold limits for your particular pet.
How can I find the wind chill right now?
Look up your city or ZIP code on the National Weather Service website to open the forecast for your location. When wind chill applies, the current conditions box lists it beside humidity and wind speed, and the tabular forecast shows it hour by hour for the days ahead. Many weather apps fold it into a feels like reading.
