Will skies be clear Monday evening over southern Ontario?

It looks like mostly clear skies are likely. Some patches of mid-level moisture and upward vertical motion are forecast to move across southern Ontario as a weak upper-level trough moves eastward from southern Ontario, but generally dry air and subsidence is forecast as a high pressure ridge builds eastward over the Great Lakes region overnight. The major exception is over regions east of Lake Huron, where lake-generated cloudiness may cause mostly cloudy skies.

So, in summary, mostly clear skies are likely over most regions of southern Ontario Monday evening.