def format_weather_header_for_HELP(itype, iunits, city, lat=None):
    """
    Prepare the header for the precipitation, air temperature and
    global solar radiation input weather datafile for HELP. The format of the
    header is defined in the subroutine READIN of the HELP Fortran source code.
    """
    fheader = [['{0:>2}'.format(itype)], ['{0:>2}'.format(iunits)], [
        '{0:<40}'.format(city[:40])]]
    if lat is not None:
        fheader.append(['{0:>6.2f}'.format(lat)])
    else:
        fheader.append([])
    return fheader
