You likely have the operating system running Cumulus with a default locale date format of YYYY-MM-DD -- it needs to be set to DD/MM/YYYY, then the $SITE['WDdateMDY'] = false; // for weather software date format of month/day/year. =false for day/month/year
in Settings.php will work.
It is the operating system that sets how Cumulus formats the date stamp.