And it's no wonder, Environment Canada says — a full month of rain dumped on the area in one day. That's the most rain that's ever fallen on an April day since at least as far back as the records go, which is 1866. So "at the RBG site, there was a full month of rain in one day." Calls about the flooding began around 7:40 p.m. as flooding cut off the main thoroughfare between Dundas and Highway 6. As for why Dundas was pummeled so hard, McKinnon said that's simply how the rain fell.

Source: CBC News April 21, 2017 13:40 UTC