Hi Henrik,
May I say, it is not correct to do so.
First thing you have to know is: When is the forecast made for your location by WU.
Then you know at what time you have to run WXSIM and after that make the log.
Otherwise you are comparing a forecast made at say 01:00 with one made at 13:00
You have to make sure the two are made around the same time, else your comparison is not correct.