Will skies be clear Friday night over southern Ontario?
It looks like a high-confidence forecast to say that skies will definitely be clear. Also, dry air (low humidity) and light northerly winds will mean that dew will not be a problem on exposed optical surfaces.

Will skies be clear Thursday evening over southern Ontario?
It looks like partly to mostly clear skies are likely over most regions. Some cloudiness is likely over regions approximately east of GTA, due partly to low-level cloudiness that may dissipate only gradually, and due to an area of mid-level moisture moving southward across Georgian Bay and central-eastern Ontario overnight. The chart below shows the forecast location of the mid-level moisture that may appear as some mid-level cloudiness (if the low-level cloudiness dissipates by sunset).

Will skies be clear over southern Ontario Wednesday evening?
Most regions will probably see some cloudiness. Significant low-level moisture is forecast to be over southern Ontario during the evening, shown in the 850 hPa level moisture chart below, and this will cause low-level cloudiness over many regions during the evening, and this low-level cloudiness will tend to diminish later in the evening or after midnight. Also, some high-level moisture may appear as cirrus-level cloudiness if there are breaks in the low cloud cover. The high-level moisture is forecast to move south of southern Ontario overnight. So, cloudy skies are more likely during mid-evening and clear skies are more likely after midnight.

Will skies be clear over southern Ontario Sunday evening?
It looks like much of southern Ontario will be under a layer of high-level cloudiness that is forecast to move southward over southern Ontario during the evening. The charts below show the location of the high-level moisture and cloudiness during the early evening. The high clouds may disappear after midnight over most regions.

Will skies be clear over southern Ontario Saturday night?
It looks like skies are likely to be quite clear, with a high pressure ridge over the Great Lakes region. A dry northerly flow of dry air over southern Ontario, with subsidence ahead of the upper level ridge, ought to result in clear skies overnight.

Where will skies be clear over southern Ontario early Saturday morning?

It looks like skies will be mostly clear over most of southern Ontario during the period between midnight and morning twilight, with some possible cloudiness mainly east of a line between the GTA and Georgian Bay, due a region of mid-level moisture that could appear as scattered cloudiness.

Will skies be clear Thursday night over southern Ontario?

It looks like mostly clear skies are likely as a high pressure ridge builds over the western Great Lakes region and a low pressure trough moves slowly eastward over eastern Ontario. A northwesterly flow of dry air and subsidence between the ridge and trough will be the main cause of clearing skies, and daytime low-level cloudiness is likely to diminish by (or shortly after) sunset.