Calculating 1000-hPa Isobaric Levels with wrf-python's wrf.vinterp()

[Bill Capehart]

Hello All:

I am hoping that I am making an obvious error in calculating 1000-hPa Isobaric Heights using WRF-Python's wrf.vinterp formula 

I am using the following command below to interpolate my z-field to isobaric levels and once I go below the ground the calculation seems to be far FAR too close to the surface terrain elevation.  

isobaric_heights = wrf.vinterp(wrfin         =.        ncf,
                               field         =      zsigma,
                               vert_coord    =  'pressure',
                               interp_levels = [1000.,500.],
                               extrapolate   =.        True,
                               field_type    =.        None,
                               log_p         =.       False,
                               timeidx       =            i,
                               method        =        'cat',
                               squeeze       =         True,
                               cache         =         None,
                               meta          =         True)

The results, when plotted are below -- showing the 1000-hPa fields in high elections mirroring the surface height rather than digging through the ground.  I get the same results if I use plog = True or False.

Is there ea netter way to do this, wither directly with WRF-Python or with support from MetPy?

Cheers and Thanks,

Bill Capehart 

South Dakota Mines.