Heat index and wind chill

Enter air temperature in Celsius or Fahrenheit, then choose heat index or wind chill. Heat index uses the U.S. National Weather Service Rothfusz regression when the simple estimate is at least 80 °F, with the low-humidity and high-humidity adjustments. Below that, it uses the NWS simple formula. Wind chill uses the 2001 NWS equation: 35.74 + 0.6215T − 35.75V^0.16 + 0.4275TV^0.16, with T in °F and V in mph.

A 32 °C afternoon at 70% relative humidity is about 90 °F and 70% humidity, which lands near 40 °C feels-like on the heat index (extreme caution). The same air at 40% humidity feels closer to the thermometer. A 0 °C reading with a 20 km/h wind is about 32 °F and 12 mph, which the wind-chill equation puts a few degrees below freezing. At −15 °C and 40 km/h the feels-like value drops into the frostbite planning band.

Presets cover a humid afternoon, extreme heat, a cold breeze, and severe cold. Heat-index bands follow the NWS chart: caution from 80 °F, extreme caution from 90 °F, danger from 103 °F, and extreme danger from 125 °F. Wind-chill frostbite times are planning approximations (about 30, 10, and 5 minutes), not a medical forecast. The heat index is intended around 80 °F and 40% humidity or higher; wind chill is intended at or below 50 °F with wind of at least 3 mph. Outside those ranges the tool still shows a number and marks it as a guide.

Nothing is uploaded. Empty values, temperatures outside −60 to 55 °C, humidity outside 0–100%, and wind above 150 km/h are rejected. The scientific temperature tool converts Celsius, Fahrenheit, and Kelvin. This one only estimates how hot or cold the air feels.