For some unknown reason, the needed script mesonet-map-json.php is has a 500-Server Error return instead of the expected JSON file.
Change mesonet-map-json.php from
<?php
at the top to be
<?php
error_reporting(E_ALL);
ini_set('display_errors','1');
so we can see what the issue may be.
No stations will be shown without having that script fully working.