base_temp does not work

Dear Colleges,

In my namelist.input I set the base_temp=290 which is also set in the WRF user guide.
However, when I convert my simulation output to potential temperature using the formula T=T+base_temp, then further converting to temperature using also pressure temp =T* pow(PP, 0.286) I have to use base_temp=300 (which is generally recommended) otherwise I have 10 degree offset compared to observations.
If base_temp=290 works or active? Or, anyway, base_temp=300 in the WRF?

Kind regards,
Artur

Arthur,
You should calculate potential temperature by:
theta = T + 300

T is perturbation potential temperature in wrfout.

Thanks a lot!