We are currently watching the risk for some scattered severe thunderstorms across portions of Southern Ontario and portions of Far Northeastern Ontario.
Southern Ontario:
Widespread showers and thunderstorms are expected to develop across the region.
Mainly non-severe risk area (blue) or marked with a '1':
Areas north of a line which extends from Cornwall to Westport, Haladar, Haliburton, MacTier, Owen Sound and Saugeen Shores can expect some non-severe thunderstorms. The main threats in this region include gusty winds near 70-80km/h, small hail, and heavy rain is possible. Flooding is a concern. An isolated storm or two may become severe towards the 'green' or '2' region such as Owen Sound, Huntsville or Wiarton.
Low risk area (green) or marked with a '2':
Areas in the Extreme South near Windsor, Leamington, Chatham, and Sarnia have the potential to support severe thunderstorms, although, model guidance does not show development in this region, hence the low risk. Storms which develop in these regions may support an isolated tornado. Further north across portions of Northern Huron and Perth Counties (Goderich, Wingham, Listowel) region, the environment could locally support some isolated severe storms. This also includes portions of Southern Bruce County near Kincardine. There is some question about 'how severe' these storms could get and whether the main area of development will be further east than this region. Storms which develop in these regions may support an isolated tornado. Towards South-Central Ontario such as Mount Forest, Markdale, Midland, Barrie, Orangeville, Shelburne, Arthur and Meaford, isolated severe thunderstorms may develop or strengthen in this region. An isolated area of rotation can't be ruled out, although, it isn't expected in this region. Towards the GTA and Lake Simcoe, areas throughout the GTA such as Toronto, Oakville, Newmarket, and Uxbridge may see some isolated severe thunderstorms move through the region, although, development in this region may be limited due to Lake Ontario. Across portions of Central Ontario such as Gravenhurst, Washago, Minden, Peterborough, and Apsley, we are watching the risk for one or two isolated severe thunderstorms. Most storms should be non-severe although there is an elevated risk compared to areas further east. Finally, along the Ontario-New York border, there is a low risk of a few strengthening thunderstorms to briefly region the severe limit. The area to watch most extends from Kingston to Brockville, although areas further north and east may be possible. The severe storms will be capable of producing 100km/h+ winds gusts, ~2cm hail and an isolated tornado. Flooding is a concern.
Moderate risk area (yellow) or marked with a '3':
Areas across the Extreme South including portions of Southwestern Ontario and the Golden Horseshoe are most at risk of some scattered severe thunderstorm watches. This risk includes everything in between Bayfield, Milverton, Guelph, Burlington, Niagara Region, Long Poing, Rodney, Strathroy and Grand Bend. This includes London, Kitchener, Woodstock, Hamilton, Brantford and Niagara Falls. Everywhere in this region is at risk of an isolated tornado. Areas in the 'area of interest' is most at risk of an isolated tornado or two. The severe storms will be capable of producing 100km/h+ winds gusts, 2-3cm hail and an isolated tornado or two. Flooding is a concern.
Northern Ontario and Northern Quebec:
Widespread showers and thunderstorms are expected to develop across Northeastern Ontario with some scattered showers and thunderstorms extending across portions of North Central and Northwestern Ontario.
Mainly non-severe risk area (blue) or marked with a '1':
Areas south of a line which extends from Attawapiskat, Missisa Lake, Fort Hope, Pickle Lake, Slate Falls, and Red Lake can expect some non-severe thunderstorms, excluding a pocket in Northwestern Ontario around Kenora, Sioux Narrows, and Fort Frances. The main threats in this region include gusty winds near 70-80km/h, small hail, and heavy rain is possible. Flooding is a concern. An isolated storm or two may become severe towards the 'green' or '2' region, especially near Ruel and Hornepayne. Non-severe thunderstorms are expected into Northern Quebec near Fort-Rupert and Île des Sept Miles. The severe thunderstorm risk will end at the Quebec-Ontario border due to the ending daytime heating limiting the risks.
Low risk area (green) or marked with a '2':
Areas across portions of Northeastern Ontario can expect some mainly non-severe thunderstorms with a low risk of a severe thunderstorm. This low risk area extends from Fort Albany south towards Mammamattawa, Ameson, Hornepayne, Nicholson, Chapleau, Sultan, Gogama, Gowganda, Kirkland Lake and everything east towards the Quebec border and James Bay. This includes Hearst, Timmins, Cochrane, Kesagami Park, Matheson, and Peterbell. Most storms should remain non-severe although an isolated severe thunderstorm with gusty winds near 90km/h, small to moderate sized hail and some heavy rain may be possible. In the 'area of interest,' there is the best risk at seeing some severe thunderstorms. There is a non-zero tornado risk in the area, although the risk is still quite low.