Apparent Temperature API

Apparent ("feels-like") temperature maths as an API, computed locally and deterministically from the official meteorological formulas — the three indices a weather app, dashboard or safety tool reports alongside the raw thermometer reading. The heat-index endpoint gives the US National Weather Service heat index from the air temperature and relative humidity using the full Rothfusz regression with its low- and high-humidity adjustments: because high humidity stops sweat evaporating, the body cannot shed heat and it feels far hotter than the thermometer — 90 °F at 70 % humidity feels like about 106 °F — and the result comes with a risk category from caution through danger to extreme danger. The wind-chill endpoint gives the 2001 NWS / Environment Canada wind chill from the temperature and wind speed, the cold-weather counterpart, with the frostbite-time risk band — 0 °F in a 15 mph wind feels like about −19 °F. The humidex endpoint gives Canada's warm-weather index from the temperature and humidity on the same Celsius scale, derived through the water-vapour pressure. Everything is returned in both °F and °C and computed locally and deterministically, so it is instant and private. Ideal for weather and outdoor apps, occupational-safety and sports tools, smart-home and HVAC dashboards, and climate and health utilities. Pure local computation — no key, no third-party service, instant. Human-comfort estimates in shade and light wind. 3 compute endpoints. For dew point and moist-air properties use a psychrometric API; for live conditions a weather API.