NaN values are coming over mountains when interpolating WRF variables to a particular pressure level using WRF-Python

[Ankan]

Dear everyone,
I want to extract some WRF variables (e.g., Geopotential height, wind variables, etc.) at a specific pressure level (e.g., 850 hPa). For extracting Geopotential Height at 850 hPa, I used the following WRF-Python code:
# Extract pressure and z/height variables for time index 0
pres = getvar(wrfin, 'pressure', timeidx=0)
ht = getvar(wrfin, 'z', timeidx=0, units='m')
# Create variable 'ht_850' for interpolation at the 850 hPa level
ht_850 = interplevel(ht, pres, 850.0)
But, after saving this array in a netcdf file, I learned that some values became NaN over high terrain regions (e.g., mountains). Why is it happening? Is it normal? Can anyone please guide me on this? That will be very helpful for me. A screenshot of the NCView visualization for geopotential height is also attached for better understanding.
Thanks and regards,
Ankan

 

[Ming Chen]

Ankan,
Where is your domain domain? Over high topography area like Tibet, 850hPa can be underground. In this case the values of some elements are NaN. .

 

[Ankan]

Dear @Ming Chen,
A screenshot of my domain is attached in the previous message. As you can see, my domain is Indian region including the surrounding Himalayas and ocean region. The values of geopotenial height at 850 hPa are NaN over the Himalayas and some high terrain regions of north-east India. So, that means over high terrain regions the geopotenial height at 850 hPa will always be NaN. Right?
With regards,
Ankan