We are currently watching the risk for scattered severe thunderstorms across a large portion of Northern Ontario, including portions of Far Northern Ontario. Overnight into Tuesday morning, we are also watching a small pocket of Extreme Southwestern Ontario for a patch of strong to isolated severe thunderstorms.
Areas in orange and marked with a '4' can expect a strong risk for severe thunderstorms. This extends from Lake of the Woods near Kenora through to Grassy Narrows and Ears Falls, including Savant Lake and Armstrong. This risk also extends in a line from Armstrong through to Gull Bay, Raith, and Shebandowan. Everything in between these lines are also included in this risk such as Fort Frances, Dryden, Savant Lake, and Atikokan. The main threats in this region are large hail between 2 and 4cm, heavy rain over 50mm and damaging winds over 100km/h. Isolated pockets of 3-6cm hail may also be possible. An isolated tornado or two is possible in this region.
Areas in yellow and marked with a '3' can expect a moderate risk for severe thunderstorms. This risk area extends from Lake of the Woods and the Manitoba border through to Deer Lake and MacDowell Lake extending into Ontario to include Summer Beaver and Missisa Lake as well. This risk also includes Ogoki and Fort Hope. Along the shores of Lake Superior such as Cloud Bay, Thunder Bay, and Nipigon are also included in this region. Severe thunderstorms are likely to develop scattered to widespread for areas south of MacDowell and Pickle Lake. The main threats are large hail between 1 and 3cm, damaging winds near and over 90km/h and heavy rain over 50mm. An isolated tornado is possible in this region. Further east towards Missisa Lake, Ogoki, Fort Hope and Summer Beaver, isolated to scattered thunderstorms, some severe are possible. The main threats are similar to risks mentioned before although the heavy rain threat increasing and hail threat decreasing towards 1-2cm hail. An isolated tornado remains possible in this region but with a lesser risk.
Areas in green and marked with a '2' can expect a low risk for severe thunderstorms. This risk extends from Opasquia through to Kingfisher Lake including Sandy Lake and Weagamow Lake. The main threats in this region are wind gusts near 90km/h, heavy rain over 50mm and moderate to large hail sized between 1 and 2cm. An isolated tornado may be possible in this region but it is questionable. Another area of a 'low' severe threat extends from Mammamattawa through to Pagwa and Schreiber, including Nakina and Jellicoe. A weakening line of thunderstorms will pass through this region and bring the threat for wind gusts near 90km/h and moderate-sized hail between 0.5 and 1.5cm. Isolated pockets of 2cm are possible. Heavy rain over 50mm is also possible. Another area of possible severe thunderstorms extends from Webequie through to Fort Albany and Moosonee, including Onakawana, Smoky Falls, Hearst, Hornepayne, Marathon and White River. A weakening line of thunderstorms, including scattered showers and thunderstorms, will pass through this region. Some of these storms may linger a severe threat, although, that is questionable. Either way, we have highlighted a low risk for severe thunderstorms over this region. The main threats would be wind gusts over 80km/h, small to moderate-sized hail and heavy rain over 30mm. An isolated tornado may be possible.
There is some question whether or not the severe thunderstorms will extend further north towards the Big Trout Lake region with non-severe further north towards Agusk Lake, although, we have went against this for our forecast. Alongside this region, areas along the shores of James Bay such as Attawapiskat may also see an isolated severe thunderstorm, but again, the risk is too low for us to include in the forecast. The main threats for any severe thunderstorm in these region include wind gusts over 80km/h, moderate-sized hail and heavy rain over 40mm. An isolated tornado may be possible.
The final risk for severe thunderstorms extends in Extreme Southern Ontario. A patch of strong to locally severe thunderstorms are expected to across portions of Michigan and move south of Lake Huron impact Sarnia, Chatham, Rodney, and Windsor. An isolated severe thunderstorm may be possible in this region. The timing of these storms will be late this evening into the early morning hours on Tuesday (1-3am).
Elsewhere, areas in blue and marked with a '1' can expect non-severe thunderstorms. There is some question whether or not a brief strong to sub-severe thunderstorm may be possible along the eastern shores of Lake Superior extending from Montreal River Harbour through to Spanish and Tobermory, including Manitoulin Island and Sault Ste. Marie. The main threats will be heavy rain from training thunderstorms and brief gusty winds.