Environment Canada is warning of “significant” rainfall this weekend for most of southern Ontario. In a lot of areas, including the Collingwood and Blue Mountains area, the rain will continue through Sunday afternoon and may be heavy at times.
A low pressure system arriving Saturday from the American Midwest will spread rain across Southern Ontario from west to east through the day. In many areas the rain will continue through Sunday afternoon and may be heavy at times. An isolated thunderstorm may accompany the rain on Saturday over Southwestern Ontario.
This unseasonably strong low pressure is expected to track just south of the Lower Great Lakes into the Northeastern United States by Sunday. This is a track that is quite uncommon during the summer.
Regions from Windsor to the Golden Horseshoe will likely receive copious amounts of rain totalling 30 to 60 millimetres. Rainfall warnings may be required. Lesser amounts, in the 20 to 40 millimetre range, are expected over Central and Eastern Ontario. Areas farther north, to the northeast of Georgian Bay, should receive even less with the rain arriving Saturday night.
Additionally, strong northeasterly winds are expected to develop Saturday with gusts generally in the 50 to 70 km/h range with the strongest winds along the Lower Great Lakes.