For Cu Potential, a positive number means there will be Cumulus clouds, a good day is typically around a 1000 (or more).
On a good day, we need a 10 degree (or more) difference between the dry temperature and dew point.
A sun percentage value of 60% or more means that the ground will warm up and clouds can develop.
Less than 50% means there may be top cover or just too much cloud about (e.g. stratus "spread out" or Cirrus "top cover").
Ideally we do not want rain. A hint of a tenth of a millimetre means the air is fairly damp and the wet/dry temperatures will be close to each other.
The 'Stars' Forecast is experimental and based on original work by Paul Scorer.
Compare sun reaching the surface (%) to boundary layer cloud cover. If boundary layer cover is close to zero, surface sun is usually 85% or higher. If less than 85% there is top cover.