def METHOD_NAME() :
    '''Make sure we've downloaded the necessary files.
       This should only have to be done once.
    '''
    if GHCNMWeatherMean.files_downloaded :
        return
    if not os.path.exists(GHCNMWeatherMean.maxtarfilename) :
        print "Downloading", GHCNMWeatherMean.maxbasename
        urllib.urlretrieve(GHCNMWeatherMean.baseurl + \
                               GHCNMWeatherMean.maxbasename,
                           GHCNMWeatherMean.maxtarfilename)
        #tar.extractall(path="foo")
        # Now we should have a directory called
        # ghcnm.v3.2.1.20130413
        # Why that? Will it change? I have no idea. So I guess
        # we'd better search for any ghcnm.v3* directory. Gah!
    if not os.path.exists(GHCNMWeatherMean.mintarfilename) :
        print "Downloading", GHCNMWeatherMean.minbasename
        urllib.urlretrieve(GHCNMWeatherMean.baseurl + \
                               GHCNMWeatherMean.minbasename,
                           GHCNMWeatherMean.mintarfilename)
    # Now we think they're both there.
    GHCNMWeatherMean.files_downloaded = True