From WeatherCat Wiki (Mahler)
Information on Weather Underground and WeatherCat
One service that WeatherCat can submit weather data to is Weather Underground. For more information on the service, you can consult the Wikipedia article on Weather Underground.
WeatherCat can submit data to Weather Underground without the need of any add-ons. To learn how to do this, consult the How Do I Send Data To Wunderground? section in the WeatherCat manual which starts at page 61 in the version-1.0 manual of WeatherCat.
Weather Underground Troubleshooting tips