Summary via EC:

 

Seaway Weather Blog

Weather summary
for Ontario and the National Capital Region
issued by Environment Canada
at 3:06 p.m. EDT Tuesday 11 July 2017.

Discussion.

On July 6th, a particularly dangerous thunderstorm that developed
over Quetico Provincial Park in Northwestern Ontario intensified as
it travelled southeastward. A tornado warning was issued at
approximately 3:40 PM EDT based on radar imagery. The next day,
aerial reconnaissance by the Provincial Ministry of Natural
Resources and Forestry showed a damage path about 100 metres wide
and up to 2 km in length across Ottertrack Lake in the extreme
southeastern part of the park which is located near the United
States border. Most trees were flattened along this damage path. As
a result of the length of the track and the dispersion in tree
damage orientation, Environment Canada has concluded that the damage
was the result of a tornado with peak winds up to 190 km/h. This…

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