Will skies be clear over southern Ontario Tuesday night?
Skies are likely to remain partly clear during the early evening, until moisture spreads northward (illustrated below) and causes increasing cloudiness over most regions by late evening. Southern regions, just north of Lakes Ontario and Erie, will probably become mostly cloudy by (or soon after) sunset and northern regions of southern Ontario may remain mostly clear until about mid-evening.

Will skies be clear over southern Ontario Monday night?

Mostly clear skies are likely, except for some high clouds that are more likely after midnight over northern regions of southern Ontario, caused by a region of mid-level moisture (illustrated below) associated with a weak upper-level weather disturbance that is forecast to move eastward across the Great Lakes region overnight.

Will skies be clear over southern Ontario Sunday night?
Skies will most likely become mostly clear before sunset, after the cloudiness that's over southern Ontario Sunday afternoon moves eastward and a high pressure ridge spreads eastward over Ontario during Sunday and Sunday night.
Then, skies are likely to become partly or mostly cloudy during mid-evening as mid-level moisture (illustrated below) and lift ahead of an upper-level trough spread southward over southern Ontario during the evening.
So, in summary, skies will most likely be mostly clear during the early evening and then become mostly cloudy.

Saturday: no updates will be posted for Saturday night.
Have a great weekend!

Will skies be clear over southern Ontario Friday night?
Cloudy skies are likely overnight, until skies become mostlyclear several hours before sunrise.
During the early morning, mid-level moisture is forecast to move eastward from southern Ontario (illustrated below for 4 am EST) and allow clearing skies to develop, except for some scattered low-level clouds that will likely form from low-level moisture that may be present.

Will skies be clear over southern Ontario Thursday night?
Skies will be mostly clear during the evening over eastern regions, near the GTHA, except for high jetstream-level cirrus that may be visible by sunset. Further west, in southwestern regions, the cirrus will most likely be covering the sky by sunset. The jetstream-level moisture (illustrated below) is forecast to increase during the evening, but mid-level moisture is forecast to move eastward during the evening and to cause mid-level cloudiness over southwestern regions early in the evening and over eastern regions of southern Ontario by late evening.

Will skies be clear over southern Ontario Wednesday night?

Clear skies are expected over all regions as a strong high pressure ridge builds eastward over southern Ontario later Wednesday and overnight. Some low-level moisture may cause some scattered low clouds to be visible during the evening until the moisture has moved east of southern Ontario by late evening.