Will skies be clear over southern Ontario Saturday night?
Partly clear skies is the best description for skies that will most likely have some cloudiness at low and mid levels. The illustration below shows some moisture forecast at mid levels during the evening, but it should be considered as an example of the situation at most levels, any time of the night, since some moisture will be present to cause some clouds in the sky over any particular region.
So, in summary, partly clear skies are likely with some cloudiness.