Computes the dew point temperature from air temperature and relative humidity using the Magnus formula.
Published for review. The Founder is checking every card himself; anything he strikes comes down the same hour.
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Inputs
temp_c (number, degrees C, required) : Air temperature.
relative_humidity_percent (number, %, required) min 1 max 100 : Relative humidity.
Outputs
dew_point_c (degrees C): Dew point temperature.
Steps
Magnus formula with the Alduchov-Eskridge coefficients: alpha = ln(RH/100) + (b*T)/(c+T), where T is temperature in C, RH is relative humidity in percent, b=17.62, c=243.12.
Dew point Td = (c * alpha) / (b - alpha), in degrees C.
Round to 2 decimals.
Valid roughly for T between -45 C and 60 C and RH between 1% and 100%.
Constants
magnus_b = 17.62 dimensionless (source: Improved Magnus form approximation of saturation vapor pressure)
magnus_c = 243.12 degrees C (source: Improved Magnus form approximation of saturation vapor pressure)
Sources
Improved Magnus form approximation of saturation vapor pressure (Journal of Applied Meteorology (American Meteorological Society), 2026-09-30T19:54:00Z) - Source of the b=17.62, c=243.12 coefficients, also reproduced by NOAA and ECMWF.