Output Location via variables within do_shortcode function

Anyone had success doing this? Something like this should work:

[php]
$weathercity = do_shortcode('[mmjs-city]');
$weatherstate = do_shortcode('[mmjs-regionname]');
echo $weathercity .', '.$weatherstate;
echo do_shortcode('[forecast location="'.$weathercity.', '.$weatherstate.'"]');
[/php]

But doesn’t

http://wordpress.org/extend/plugins/wunderground/