root_grp = Dataset('C:/Users/ralei/Desktop/test.nc', 'w', format = 'NETCDF4')
root_grp.descritpion = 'Example temperature data'

#dimensions
root_grp.createDimension('lat', 94)
root_grp.createDimension('lon', 192)
root_grp.createDimension('temp', None)

temps = root_grp.createVariable('temp', 'f8', ('difference'))
latitudes = root_grp.createVariable('latitude', 'f4', ('lats',))
longitudes = root_grp.createVariable('longitude', 'f4', ('lons',))

lat = lats[:]
lon = lons[:]
temps = difference[:]

root_grp.close()