def write_alarm_msg(radar_name, param_name_unit, date_last, target, tol_abs,
                    np_trend, value_trend, tol_trend, nevents, np_last,
                    value_last, fname):
    """
    writes an alarm file

    Parameters
    ----------
    radar_name : str
        Name of the radar being controlled
    param_name_unit : str
        Parameter and units
    date_last : datetime object
        date of the current event
    target, tol_abs : float
        Target value and tolerance
    np_trend : int
        Total number of points in trend
    value_trend, tol_trend : float
        Trend value and tolerance
    nevents: int
        Number of events in trend
    np_last : int
        Number of points in the current event
    value_last : float
        Value of the current event
    fname : str
        Name of file where to store the alarm information

    Returns
    -------
    fname : str
        the name of the file where data has written

    """
    with open(fname, 'w', newline='') as txtfile:
        txtfile.write(
            'Weather radar polarimetric parameters monitoring alarm\n')
        if radar_name is not None:
            txtfile.write('Radar name: '+radar_name+'\n')
        txtfile.write('Parameter [Unit]: '+param_name_unit+'\n')
        txtfile.write('Date : '+date_last.strftime('%Y%m%d')+'\n')
        txtfile.write('Target value: '+str(target)+' +/- '+str(tol_abs)+'\n')
        if np_trend > 0:
            txtfile.write(
                'Number of points in trend: '+str(np_trend)+' in ' +
                str(nevents)+' events\n')
            txtfile.write(
                'Trend value: '+str(value_trend)+' (tolerance: +/- ' +
                str(tol_trend)+')\n')
        else:
            txtfile.write('Number of points in trend: NA\n')
            txtfile.write('Trend value: NA\n')
        txtfile.write('Number of points: '+str(np_last)+'\n')
        txtfile.write('Value: '+str(value_last)+'\n')

        txtfile.close()

    return fname