Campbell Scientific VisualWeather Software - Manual (Page 75)

Appendix F. Heat Index
F.1 Heat Index
Heat index is the perceived temperature as influenced by relative humidity.
For example, an air temperature of 90°F would feel like 132°F if the RH was
100%.
The equation is only useful if air temperature > 80°F (27°C) and relative
humidity > 40%. VisualWeather will report the wind chill as N/A if air
temperature is < 80°F (27°C) or relative humidity < 40%.
F.1.1 Method
Heat index equivalent temperature (°F) can be obtained by using the following
equation
[1] .
HI = -42.379 + 2.04901523T + 10.14333127R - 0.22475541TR - 6.83783x10 -
3 T 2 - 5.481717x10 -2 R 2 + 1.22874x10 -3 T 2 R + 8.5282x10 -4 TR 2 - 1.99x10 -6 T 2 R 2
where, HI = heat index in °F, T = air temperature in °F, and R = relative
humidity in percent (e.g., 30).
VisualWeather calculates heat index from raw data of average values of
temperature and relative humidity. Users need not enter any parameters to
calculate heat index.
F.2 References
1. The equation used in this calculation is from the National Weather
Service; a good explanation may be found at
http://www.srh.noaa.gov/bmx/tables/hindex.html
2. Campbell Scientific also has a "Heat Index" Application Note at
ftp://ftp.campbellsci.com/pub/outgoing/apnotes/heatindx.pdf
F-1