We are watching the risk for some isolated to scattered severe thunderstorms across portions of Northeastern Ontario this evening and into the overnight.
Into the evening, a line of thunderstorms will move across Michigan and Lake Superior and pass through portions of Northeastern Ontario between Lake Huron and Lake Superior. Isolated thunderstorms may develop along and around the line of thunderstorms before the storms move into Northeastern/Central Ontario. The line of storms could begin to 'bow' creating a line of damaging wind. The storms will weaken into the early morning as the line of storms pass into Central and Eastern Ontario, including portions of Quebec.
Areas in orange and marked with a '4' can expect a strong risk for severe thunderstorms. This risk extends from Batchawana Bay through to Searchmont and Thessalon, including Sault Ste Marie. Damaging winds between 80 and 100km/h, locally 110km/h are possible. Heavy rain between 20 and 40mm are possible, locally over 50mm. Moderate sized hail between 0.5 and 1.5cm is also possible. An isolated tornado is possible in this region.
Areas in yellow and marked with a '3' can expect a moderate risk for severe thunderstorms. There are two different regions within this risk area. The first risk area extends from Wawa through to Ranger Lake including Lake Superior Park and Montreal River Harbour. Heavy rain between 30 and 50mm, moderate to large hail between 1 and 2cm and gusty winds between 70 and 100km/h are possible in this region. An isolated tornado is also possible in this region. The second risk area extends from Elliot Lake through to Espanola and much of Manitoulin Island. The main threats in this secondary region including damaging winds between 80 and 110km/h, heavy rain and moderate sized hail, similar to previously mentioned. An isolated tornado is possible west of Blind River towards Sault Ste. Marie.
Areas in green and marked with a '2' can expect a low risk for severe thunderstorms. This extends from Puskakwa Park through to White River, Nicholson and Sultan, including Chapleau. There is some question whether storms will develop in this region. If severe storms do, heavy rain and brief gusty winds will be the main threats. An isolated pocket of moderate to large hail is also possible. Further northeast towards Timmins, Cochrane and Matheson, there is even more question as to whether thunderstorms will develop. If thunderstorms develop in this region, there is an isolated severe risk. Further south extending from Sudbury through to North Bay, Britt, Parry Sound and the northern part of the Bruce Peninsula including Tobermory, damaging winds and heavy rain will be the main threat from a weakening line of thunderstorms.
Into the early morning hours on Thursday, an isolated strong to severe thunderstorm may be possible from the Simcoe/Muskoka region through to Algonquin from a weakening line of thunderstorms. Due to the expected location where the storms will become sub-severe, we have not included this region on the forecast map.
Elsewhere, areas in blue and marked with a '1' can expect some isolated to scattered non-severe thunderstorms. The main threats will be heavy rain and brief gusty winds. Small hail is possible.
Looking forward, we will be closely watching Thursday afternoon and evening across the Ottawa Valley for severe thunderstorms, including the risk for isolated tornado(s).