As mentioned in the title the pandas data frame includes everything else relative humidity although that data is part of the sounding.
Why ?
Index(['pressure', 'height', 'temperature', 'dewpoint', 'direction', 'speed', 'u_wind', 'v_wind', 'station', 'station_number', 'time', 'latitude', 'longitude', 'elevation', 'pw'], dtype='object'