foreach $year ( sort keys %weather_archive ) {
  print "$year\n";
  foreach $month ( keys %{$weather_archive{$year}} ) {
    print "  $month\n";
    foreach $day ( sort keys %{$weather_archive{$year}{$month}} ) {
      print "$day\n";
      foreach $measurement ( keys %{$weather_archive{$year}{$month}{$day}} ) {
        print "$measurement:  $weather_archive{$year}{$month}{$day}{$measurement}\n";
      }
    }
  }
}