Apparent temperature · NWS rule
Feels Like Temperature Calculator
The feels-like temperature is the single number forecasts use for how the weather will feel on skin. In the cold it is the wind chill, in the heat it is the heat index, and in between it is simply the air temperature.
Formula
- Air temperature ≤ 50°F (10°C) and wind ≥ 3 mph: NWS 2001 wind chill.
- Air temperature ≥ 80°F (27°C): NWS heat index (Rothfusz regression with its adjustments).
- Otherwise: the air temperature.
Source: The rule the National Weather Service uses for apparent temperature in its forecasts, combining the NWS wind chill index (2001) and the NWS heat index.
Valid range
- Each branch inherits its formula’s limits: wind chill needs wind of at least 3 mph, and the heat index is flagged above 110°F, where the regression is extrapolated.
- Between 51°F and 79°F no adjustment applies, so feels-like equals the air temperature. Humidity is only used in the heat branch and wind only in the cold branch.
- Weather apps differ: some use the Australian apparent temperature (Steadman 1994), which also counts wind in warm weather, so their feels-like can differ from the NWS value.
Why “feels like” changes formula
There is no single equation that captures both the cold and the heat well. In the cold, wind dominates how fast you lose heat; in the heat, humidity dominates how well you can cool down. NWS therefore switches between its two indices and, in the mild middle, reports the air temperature unchanged.
That switch is why the feels-like number can jump between categories without a big change in the weather: at 50°F with a 10 mph wind it reports the wind chill, while at 51°F it reports the air temperature.
Other services make different choices. Some use Steadman’s 1994 apparent temperature, which blends temperature, humidity and wind into one formula at every temperature. The feels-like figure on WeatherPerch forecast pages comes from Open-Meteo’s apparent temperature, which also counts sunshine, so it can differ from this calculator by a few degrees. Neither approach is wrong, but the numbers are not interchangeable.
Worked examples of the NWS feels-like rule
Generated from the same equation as the calculator above.
| Air temperature | Humidity | Wind | Formula used | Feels like |
|---|---|---|---|---|
| 20°F (−7°C) | 60% | 15 mph (24 km/h) | Wind chill | 6°F (−14°C) |
| 35°F (2°C) | 70% | 10 mph (16 km/h) | Wind chill | 27°F (−3°C) |
| 50°F (10°C) | 60% | 5 mph (8 km/h) | Wind chill | 48°F (9°C) |
| 65°F (18°C) | 50% | 10 mph (16 km/h) | Air temperature | 65°F (18°C) |
| 75°F (24°C) | 80% | 5 mph (8 km/h) | Air temperature | 75°F (24°C) |
| 85°F (29°C) | 60% | 5 mph (8 km/h) | Heat index | 89°F (32°C) |
| 95°F (35°C) | 50% | 10 mph (16 km/h) | Heat index | 105°F (41°C) |
| 100°F (38°C) | 30% | 5 mph (8 km/h) | Heat index | 102°F (39°C) |
Feels-like temperature questions
- What does “feels like” mean in a forecast?
- It is the apparent temperature: how warm or cold the air feels on exposed skin once wind or humidity is taken into account. In NWS forecasts it is the wind chill when it is cold and windy, the heat index when it is hot, and the air temperature otherwise.
- Why does my weather app show a different feels-like temperature?
- Apps use different formulas. Some follow the NWS rule used here, while others use the Australian apparent temperature (Steadman 1994), which also factors wind into warm weather, or their own blend. The inputs (which wind speed, which humidity reading) can differ too.
- Why is humidity ignored when it is cold?
- The NWS wind chill formula uses only temperature and wind, because humidity has little effect on how quickly dry skin loses heat in cold air. Humidity only enters the feels-like value once the heat index applies at 80°F.
- Why does feels-like equal the temperature on mild days?
- Between about 51°F and 79°F neither index is designed to apply, so NWS reports the air temperature. A breeze or sunshine still changes how it feels, but not the official number.