The advforecast2.php V4 uses forecast.weather.gov as a source, the V5 uses api.weather.gov. There may have been an issue with forecast.weather.gov that connected, but wouldn't finish a GET and so hung the site. There's nothing on the
NCEP Ops messages site about a failover/failure, so I'm suspecting it was a local (your website to the source website) issue that seems to have cleared.
I just loaded your page with no issues.