Calling prn2wth without arguments will show the command line syntax:
prompt> prn2wth
Usage: prn2wth <prn filename> <wth filename> <lat> <long> <ISO8601 time>
The prn filename is the input PRISM weather file. The wth filename specifies the name of the DIRSIG weather file being generated. The lat and long are used to model the diffuse and optionally the direct insolation. The date given by ISO8601 time is also needed for modeling insolations.
The following screen shot gives an example of using prn2wth. It converts "mls.prn" to "mls.wth", using 43.12 North and 77.67 West for latitude and longitude, and using June 24, 1996 for the date.
prompt> prn2wth mls.prn mls.wth 43.12 77.67 1996-06-24T13:23:59.5900-05:00
Note that the current release uses the odd convention that a "West" longitude is a positive number.