The next weather system will be quick to move in behind the last one, with rain showers moving into southern Ontario on Friday. This timing is agreed on by a few models, so I have the rain chance fairly high, at 60%. I'm not quite ready to pin down the timing more specifically than that at this point, but I will say that the afternoon hours will have a higher chance than the morning hours. That could change as we get closer to Friday. Thunderstorms will also be a possibility as the upper level jet will be positioned to aid lifting on top of some instability. While it is too early to forecast rain amounts this far out, it looks like the rain could be heavy at times.
The surface low will move to the east of CTMP by Saturday morning, taking most of the rain with it. However, the upper level trough will lag behind the surface low, which may keep a few showers around into Saturday. If there is rain Saturday, I expect that it will be light and short-lived. showers. There will be a pretty good pressure gradient that will produce some breezy conditions and gusty winds on Saturday.
A northwest flow develops through the atmosphere, bringing drier air and high pressure to CTMP on Sunday. The weather for the race should be really nice, with mostly sunny skies and highs in the upper 70s. Winds will be lighter than Saturday, but still around 10 mph.
Here's the forecast graphic in degrees C and KM/H for our Canadian followers: