def get_gap_HS_data(modeling_data, gap_period, gap_station):
    """
    Get original HS data in the gap period. Only winter values (Nov-Apr) will 
    be returned.
    """
    y_true = (modeling_data
              .loc[modeling_data['stn']==gap_station, 'HS']
              .loc[gap_period]
              )
    y_true = y_true.loc[y_true.index.month.isin([11,12,1,2,3,4])]
    y_true.name = f'Measured HS Data'
    return y_true