Almost all free weather websites and smartphone apps use data from the United States GFS global weather model as it is the only one openly published for all to use. But for cloud forecasts in the Australian region, there are two significantly better (although less user friendly) options you should also be looking at. All up then, here are my three recommended sources for cloud forecasts in the Australian region:
1) Synthetic Satellite Forecast Loop from the Australian Bureau of Meteorology ACCESS model: Australian Region Forecast Loop.
2) European Model forecast via the Norwegian site yr.no (the only site I know of that publishes European Model data: e.g. Heathcote, Victoria. Search for your nearest largest town, then choose 'Hour by Hour' and 'Detailed' to see the full cloud breakdown for high/medium/low cloud.
3) US Model via Skippy Sky: This is the best display of GFS data and the most user friendly of these three options. I would place greater weight on the previous two models though, particularly for short-term forecasts.