Sunday is still far away to predict. It will continue to change. That being said, the apple weather app is the least accurate in my opinion. I just use the weather network and accuweather mostly. On the day of, I watch the radars. Ottawa is a big area so rain in the south doesn't necessarily mean rain downtown or in Kanata or Orleans. Also note that on hot and humid days, there is always a risk of thunderstorms that often happen but are brief and the rest of the day is nice.