Saturday night: clear skies will be caused by a big high pressure ridge and clear, dry air over southern Ontario.

Will skies be clear over southern Ontario Friday night?

Clearing skies are expected over some regions, after moisture moves eastward with a low pressure region (illustrated below for low-level moisture during late evening), but regions near Lake Ontario and the GTHA are likely to remain cloudy until after midnight and then clouds are likely to persist over regions south of Lake Huron and Georgian Bay overnight.

Will skies be clear over southern Ontario Thursday night?
Mostly clear skies are expected, except for some low and mid-level clouds that may appear occasionally.

Will skies be clear over southern Ontario Wednesday night?
Mostly clear skies are likely except for some low and mid-level clouds that may be visible during early evening.

Will skies be clear Tuesday night over southern Ontario?
Mostly clear skies are expected, except for some patches of mid-level clouds that may occasionally appear over most regions.

Saturday night: clear skies are expected.

Will skies be clear over southern Ontario Friday?
Clear skies are expected, except for some thin high cloud that is spreading northward over regions north of Lakes Erie and Ontario.

Will skies be clear over southern Ontario Thursday night?
Partly clear skies are expected, with some clouds likely to be in the sky over most regions, caused by a region of mid-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?
Mostly clear skies are likely and some clouds are likely to appear over some regions, due to some mid-level moisture which is forecast to be over southern Ontario overnight (illustrated below for late evening). Fog is also likely to develop over many areas.

Will skies be clear over southern Ontario Tuesday night?
Mostly cloudy skies are likely, due to lots of moisture in the atmosphere over southern Ontario, but some areas of less cloudiness may allow the brighter stars to become visible and give the impression of partly clear skies. The high humidity is likely to contribute to fog formation overnight.

Note: no posts will be updated until Tuesday, September 19.
Clear skies!

Will skies be clear over southern Ontario Thursday night?

Mostly clear skies are expected over most regions, except for some low-level cloudiness in regions near the GTA during the evening, until low-level moisture (illustrated below for late evening) is forecast to diminish and allow skies to become clear. Fog is likely to form before morning in many regions and the high humidity will cause significant dew during the night.

Will skies be clear over southern Ontario Wednesday night?
Mostly cloudy skies are expected, due to moisture from the storm south of Ontario that was Hurricane Irma, but gaps in the moisture may allow occasional periods of partly clear skies over some regions (especially northern regions closer to Georgian Bay than Lake Erie) overnight that may be clear enough to allow aurora to be seen if the aurora becomes active.

Will skies be clear over southern Ontario Tuesday night?

Mostly cloudy skies are likely over southwestern regions, due to high-level clouds moving north ahead of post-tropical storm Irma, while mostly clear skies are likely further north over northern regions of southern Ontario (approximately north of Lake Ontario, depending on how far north the high clouds remain visible during the night).

Will skies be clear over southern Ontario Monday night?

Partly clear skies are expected, due to dry air associated with a strong high pressure ridge over Ontario, except for high-level clouds that will likely be spreading northward from Tropical Storm Irma and will probably be visible over southern regions during most of the night and over most other regions during at least part of the night.

Note, no more posts will be updated until Monday September 11 (due to vacation).

Will skies be clear over southern Ontario Friday night?
Mostly cloudy skies are expected over most southern regions, due to high-level cloudiness spreading northward over southern Ontario ahead of the remnant of Hurricane Harvey, illustrated below. The high cloudiness may occasionally be thin enough to allow the moon and brighter stars to give the impression of clear skies over some regions. Some northern regions are likely to remain mostly clear, depending on how far northward the high cloud can spread before getting dispersed in the high pressure ridge over northern Ontario.