Will skies be clear over southern Ontario Monday night?
Mostly cloudy skies are expected, due to lots of high cloud, although the high cloud cover may occasionally be thin enough to allow the brighter stars and planets to be clearly visible and give the impression of a mostly clear sky.

Will skies be clear over southern Ontario Sunday night?
Skies are likely to be partly cloudy due to lots of high cloud, due to jetstream-level moisture which is forecast to be over southern Ontario overnight (illustrated below for late evening), and some low and mid-level cloud may also be over some regions during the evening.

Will skies be clear over southern Ontario Friday night?

Lots of cloudiness is likely, due to lots of mid and low-level moisture over southern Ontario overnight (illustrated below for late evening) as well as some high cloud with the jetstream over southern Ontario, but lots of partly clear periods are also likely.

Will skies be clear over southern Ontario Thursday night?
Clearing skies are expected during the evening over most regions as moisture gradually moves eastward from southern Ontario and from regions near western Lake Ontario by about midnight (illustrated below for mid-level moisture during late evening).

Will skies be clear over southern Ontario Wednesday night?
Mostly clear skies are expected except for some clouds that may appear over some regions occasionally due to some low-level moisture which is forecast to be over southern Ontario overnight (illustrated below for late evening).

 Will skies be clear over southern Ontario Friday night?

Cloudy skies are expected over southwestern regions. Further east, partly clear skies are likely over some regions during the evening and will likely allow the moon and brighter stars to be visible before more extensive mid and high-level moisture and cloud moves eastward across all of southern Ontario (illustrated below for late evening).

Will skies be clear over southern Ontario Thursday night?
Mostly clear skies are expected, except for increasing high cloudiness over southwestern regions during the evening and then over other regions later in the night, due to increasing jetstream-level moisture which is forecast to move eastward over southern Ontario overnight (illustrated below for late evening).

Will skies be clear over southern Ontario Wednesday night?

Clear skies are expected, except for some increasing high cloud that may appear over southwestern regions by morning, due to increasing jetstream-level moisture which is forecast to move eastward over the central Great Lakes region overnight (illustrated below for the hour before sunrise).

Will skies be clear over southern Ontario Monday night?
Cloudy skies during the evening are likely to begin clearing before morning, as moisture moves southeastward from southern Ontario overnight (illustrated below for early Tuesday).

Will skies be clear over southern Ontario Sunday night?
Partly clear skies are expected over most regions, except for more cloudiness likely over southwestern regions, due to increasing mid-level moisture over those regions (illustrated below for Sunday night on 700 mb moisture chart) and except for some high thin clouds that may occasionally appear, due to increasing jetstream-level moisture (illustrated below for early Monday).

Will skies be clear over southern Ontario Saturday night?
Clearing skies are expected after midnight, but fog is likely to form in the regions where the sky clears.

Will skies be clear over southern Ontario Friday night?
Mostly cloudy skies are likely over most regions, except for partly cloudy skies over southwestern regions, where mid-level moisture is forecast to be less extensive than other regions (illustrated below for late evening).

Will skies be clear over southern Ontario Wednesday night?

Clear skies are expected, except for some cirrus cloud that may appear over most regions, due to jetstream-level moisture which is forecast to move southeastward over southern Ontario especially after midnight (illustrated below for early Thursday) and due to jetstream winds over southern Ontario.

Will skies be clear over southern Ontario Tuesday night?
Clear skies are expected, but some thin, high jetstream-level cirrus may appear over some regions due to a strong jetstream which is forecast to be over southern Ontario overnight (illustrated below).

Will skies be clear over southern Ontario Monday night?

Clear skies are likely during the evening over most regions and then increasing cloudiness is expected after midnight over most regions due to increasing moisture (illustrated below for early Tuesday) spreading southward over southern Ontario after midnight.

Extra: related to the Aldebaran graze event: updated moisture forecast charts are shown for Monday morning's updated GFS model (although similar to NAM model output shown in the images above):

Will skies be clear over southern Ontario Sunday night?

Clear skies are forecast.

Also:

Will skies be clear over Earlton, ON during the Aldebaran lunar graze occultation event http://www.lunar-occultations.com/iota/bstar/0710zc692.htm Tuesday morning (time, approx. UTC 08:30)?

Skies may be clearing by occultation time. Forecast models predict a region of moisture at 700 mb level (generally causing mid-level cloudiness) to be moving southward from the Earlton area around 09 UTC but more widespread moisture at the 850 mb level over the area. While humidity generally <70% doesn't mean widespread cloud, upward motion (such as ahead of a warm front) can cause it to be widespread cloudiness, while strongly descending air (such as following a strong cold front) can mean dissipating cloud. In this case, a cold front is forecast to move southward over Earlton overnight Monday night and be near Toronto by sunrise Tuesday but strong subsidence is not forecast following the front. The moisture which is forecast to be over Earlton could dissipate by occultation time, but may remain as a scattered or broken layer of clouds that doesn't dissipate until either dry air moves over it and mixes with the moisture to reduce the relative humidity and cause the clouds to dissipate, or else waits until vertical mixing and convection begins after sunrise to help mix the moisture out and cause dissipating clouds.

In this case for 09  UTC Tuesday, the nearby presence of lots of moisture implies a significant risk of cloudiness (possibly broken overcast or just scattered clouds) until several hours after sunrise. But, it could also be read as clearing skies, and possibly even mostly clear skies, by occultation time.

Below are forecast charts for moisture at 850 and 700 hPa levels from GFS model and latest NAM model.

Saturday night: clear skies

Will skies be clear over southern Ontario Friday night?
Clear skies are expected, except for thin, high jetstream-level clouds that may appear occasionally due to the position of the jetstream over southern Ontario overnight (illustrated below for late evening).

Will skies be clear over southern Ontario Thursday night?

Cloudy skies during the evening are likely to begin clearing after midnight and by morning twilight when most of the moisture following Thursday evening’s cold front moves southward from southern Ontario (illustrated below for early Friday).

Will skies be clear over southern Ontario Wednesday night?
Mostly clear skies are likely, except for some clouds at low, middle and high levels that are likely to appear, especially over southwestern regions, due to moisture which is forecast to gradually increase over southwestern Ontario overnight (illustrated below for late evening).

Will skies be clear over southern Ontario Tuesday night?
Clear skies are expected, except for some high jetstream-level clouds that may appear over some locations, and except for some low clouds that may appear occasionally, caused by increasing low-level moisture over southern Ontario overnight (illustrated below for early Wednesday).

Will skies be clear over southern Ontario Monday night? Mostly clear skies are expected, except for some clouds that may appear occasionally over regions north of Lake Erie during the evening and especially over the Niagara peninsula, caused by low-level moisture gradually moving eastward from southern Ontario overnight (illustrated below for late evening).