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Dave, There may not be a built-in formal to calculate relative humidity, but this can easily be achieved through Jython. In fact, there is a very similar example here to calculate dew point from the temperature, and relative humidity: http://www.unidata.ucar.edu/software/idv/docs/workshop/isl/JythonScripting.html You will have to choose an approximation to calculate relative humidity that you are satisfied with. I found a "Bulletin of the American Meteorological Society" (BAMS) paper that describes various methods to achieve this calculation. http://journals.ametsoc.org/doi/pdf/10.1175/BAMS-86-2-225 Best Wishes, Unidata IDV Support > Full Name: dave > Email Address: address@hidden > Organization: china, NMC > Package Version: 5.0 build date:2014-01-09 08:05 UTC > Operating System: Windows 7 > Hardware: Java: home: C:\Program Files\IDV_5.0\jre version: 1.6.0_43 > j3d:1.5.2 fcs (build4) > Description of problem: Hi, > With IDV jython, how to calculate relative humidity from temp and dewpoint > temp? > Is there any existing function to do this? Very thanks! > dave > > Ticket Details =================== Ticket ID: XGO-279218 Department: Support IDV Priority: Normal Status: Closed