Will skies be clear over southern Ontario Saturday night?
The northern edge of a region of jetstream-level moisture (illustrated below with the output chart from one forecast model) will most likely be the dividing line across southern Ontario between clear skies to the north, and partly cloudy skies to the south due to high thin cloudiness that will probably be easy to see in the bright moonlight.

Will skies be clear Friday night over southern Ontario?

Skies will probably appear to be mostly clear, except for some high cloudiness over most regions, and especially southwestern regions, caused by jetstream-level moisture (illustrated below) that may be visible in the bright moonlight, as well as some mid-level cloudiness that may appear over eastern regions of southern Ontario during the evening, caused by some mid-level moisture (illustrated below) that is forecast to be near or east of the GTA.

Will skies be clear Thursday night over southern Ontario?

It looks like lots of jetstream-level moisture (illustrated below) will cause high cloudiness over all of southern Ontario, and thicker mid-level cloudiness will also move over many regions.

Will skies be clear over southern Ontario Wednesday night?

Mostly clear skies are expected, except for some scattered high-level clouds that could become visible, caused by mid-level moisture that is forecast to move over parts of southern Ontario overnight (illustrated below), and except for fog patches that may form over some regions before morning.

Tuesday night: clear skies are expected over southern Ontario.

Will skies be clear over southern Ontario Monday night?
Skies are likely to be clear by sunset and remain clear overnight, except for possible high clouds remaining over easternmost regions of southern Ontario during sunset and early evening, as a patch of high cloudiness over southern Ontario during Monday (associated with a weak mid-level weather disturbance south of Lake Ontario) gradually moves northeastward during the afternoon.

Will skies be clear over southern Ontario Sunday night?

Skies will most likely be partly to mostly clear, except for high cloudiness over most regions caused by some jetstream-level moisture (illustrated below) moving eastward across southern Ontario overnight.