How to calculate mean values grouped on another column

You could groupby on StationID and then take mean() on BiasTemp. To output Dataframe, use as_index=False

In [4]: df.groupby('StationID', as_index=False)['BiasTemp'].mean()
Out[4]:
  StationID  BiasTemp
0        BB       5.0
1     KEOPS       2.5
2    SS0279      15.0

Without as_index=False, it returns a Series instead

In [5]: df.groupby('StationID')['BiasTemp'].mean()
Out[5]:
StationID
BB            5.0
KEOPS         2.5
SS0279       15.0
Name: BiasTemp, dtype: float64

Read more about groupby in this pydata tutorial.