Southern Ontario: Thunderstorm Outlook for Monday, July 5, 2021

Forecast Discussion

A very stormy start to the week is expected throughout Southern Ontario as hot, humid temperatures will lead to a fairly strong risk for thunderstorms with some of them reaching severe levels on Monday. The current target zone includes the shoreline around Georgian Bay and the northern parts of Lake Huron where we expect storms to develop sometime during the mid to late afternoon hours and track to the east or southeast.

This severe risk will also encompass the northern GTA and into parts of Central and Eastern Ontario with the main threat being damaging wind gusts over 100km/h as the line of mature storms sweeps across the region around the dinner hour. As for the tornado risk, it’s very questionable as the general storm mode favours more of a wind risk rather than tornadoes or large hail. Regardless, we’ve included a tornado risk on our map around Georgian Bay as there are some indications that a slight chance of a tornado or perhaps even a tornadic waterspout over Lake Huron or Georgian Bay that comes onshore is possible earlier in the lifespan of these storms.

The storm threat will continue late into the evening as the line of storms progresses into Eastern Ontario. It looks like the storms should weaken enough by midnight that they won’t pose a severe risk, but strong winds and heavy rainfall could continue to be an issue even into Extreme Eastern Ontario along the international border.