Will skies be clear over southern Ontario Thursday night?
Mostly cloudy!
Lots of mid and low-level moisture.

It looks like partly clearing skies are likely over some or most regions of southern Ontario overnight as mid-level moisture moves northeastward from southern Ontario (as in the chart below) but many regions will experience some lake-effect cloudiness due to low-level moisture flowing eastward from Lake Huron and Georgian Bay.

Will skies be clear Friday night over southern Ontario?

It looks like skies will remain mostly clear during the evening, without interference from pesky lake-effect cloudiness, but increasing mid to high-level moisture ahead of an approaching warm front is likely to appear over southern Ontario before early morning.

Will skies be clear over southern Ontario Monday night?

Clearing skies are expected by sunset as deep moisture moves eastward from southern Ontario following Monday's cold front, except for some low-level cloudiness especially over regions east of Lake Huron and Georgian Bay, and so partly clear skies are likely over most regions overnight.

Will skies be clear over southern Ontario Friday night?
It looks like mostly clear skies are likely, except for low-level clouds that will probably move across most regions from time to time during the night and will be more common over regions south and east of Lake Huron and Georgian Bay.

Will skies be clear Monday night over southern Ontario:

It looks like skies may become mostly clear within several hours after sunset, but lots of jetstream-level moisture will most likely be visible as cirrus cloud in the bright moonlight.

Will skies be clear over southern Ontario Saturday night?
Skies will most likely be mostly clear by sunset, except for some low-level moisture that may cause low-level clouds to be visible over some regions during the evening, particularly south of Georgian Bay and Lake Huron. Then, clear skies are expected overnight.