Stationsweb Help - Apparent Temperature
The apparent (“feels like”) temperature combines air temperature, humidity, wind speed and solar radiation (where available) to calculate a perceived temperature. Multiple calculation methods are available, each using a different combination of these inputs — not all methods use all four. The available methods are described below. The apparent temperature is shown on the widgets page, and the preferred method can be selected in the station operator settings.
Apparent Temperature Categories
A category is shown for the current apparent temperature based on the Universal Thermal Climate Index scale:
| Temperature Range | Category |
|---|---|
| above 46 °C (115 °F) | Extreme heat stress |
| 38 °C – 46 °C (100 °F – 115 °F) | Severe heat stress |
| 32 °C – 38 °C (90 °F – 100 °F) | Strong heat stress |
| 26 °C – 32 °C (79 °F – 90 °F) | Moderate heat stress |
| 9 °C – 26 °C (48 °F – 79 °F) | No thermal stress |
| 0 °C – 9 °C (32 °F – 48 °F) | Slight cold stress |
| -13 °C – 0 °C (9 °F – 32 °F) | Moderate cold stress |
| -27 °C – -13 °C (-17 °F – 9 °F) | Strong cold stress |
| -40 °C – -27 °C (-40 °F – -17 °F) | Severe cold stress |
| below -40 °C (-40 °F) | Extreme cold stress |
Source: Bröde, P., Fiala, D., Błażejczyk, K. et al. Deriving the operational procedure for the Universal Thermal Climate Index (UTCI). Int J Biometeorol 56, 481–494 (2012).
Calculation Methods
Universal Thermal Climate Index (UTCI)
Uses air temperature, wind speed, humidity and solar radiation to calculate an apparent temperature. UTCI is the most comprehensive method and is suitable for a wide range of climatic conditions.
Source: Bröde, P., Fiala, D., Błażejczyk, K. et al. Deriving the operational procedure for the Universal Thermal Climate Index (UTCI). Int J Biometeorol 56, 481–494 (2012).
Australian Apparent Temperature
Calculation method as defined by the Australian Bureau of Meteorology. Uses air temperature, humidity and wind speed. The variant including solar radiation is not used, as it has proven unreliable.
Source: Steadman, R. G. (1994). Norms of apparent temperature in Australia. Aust. Met. Mag, 43, 1–16.
Environmental Stress Index (ESI)
Uses air temperature, wind speed, humidity and solar radiation to derive an apparent temperature. Primarily developed for and used in hot climates.
Source: Moran, D. S. et al. An environmental stress index (ESI) as a substitute for the wet bulb globe temperature (WBGT). Journal of Thermal Biology, Volume 26, Issues 4–5, 2001, Pages 427–431.
Combined Wind Chill and Heat Index
Uses wind chill and heat index in combination. Since the defined ranges of the two indices do not overlap, they are applied concurrently without conflict. For value combinations that fall outside the definition range of both indices, the air temperature is used directly with no correction applied.
Humidex
Uses only air temperature and humidity — wind speed and solar radiation are not taken into account. Best suited for hot and humid conditions; results may be less representative in other situations.
Source: Steadman, R. G. (1979). The Assessment of Sultriness. Part I: A Temperature-Humidity Index Based on Human Physiology and Clothing Science. J. Appl. Meteor. 18, 861–873.