def get_ts_tick_labels_monthly(df):
    """
    get_ts_tick_labels_monthly

    Function for producing cleanly-formatted tick labels for DataFrames
    with a time-series index, one per week

    INPUTS:
        df - DataFrame with datetime Index from which to extract
             tick labels for plotting

    OUTPUTS:
        tick_labs - array of tick labels (one per month, minimally complex)

    """
    tick_labs = df.index.strftime('').values
    is_first_week_of_month = df.index.day <= 7
    is_first_week_of_year = df.index.dayofyear <= 7
    tick_labs[is_first_week_of_month] = df.index[is_first_week_of_month
        ].strftime('%b')
    tick_labs[is_first_week_of_year] = df.index[is_first_week_of_year
        ].strftime('%b\n%Y')
    return tick_labs
