Thank you very much!WRF doesn't have the capability to output PVT. The following documents may provide general information how to do the calculation.
(1) Compute Isentropic Potential Vorticity on hybrid levels
CCM Processor User's Guide: May 1994: page B-19
Original source P Rasch and B Boville
(2) A nice basic discussion of PV may be found at:
Mid-Latitude Atmospheric Dynamics: A First Course
Jonathan E. Martin, Wiley 2006, QC880.M36 , pp276-onward