Travelling for 2 km and with a width of 300 metres, this F0 tornado destroyed a gazebo and tore branches off of trees just to the west of Grimsby.
Figure 1 depicts the surface observations at 2:00 pm EDT, which shows a cold front moving across Hamilton. This front triggered thunderstorms across southwestern Ontario, which ultimately led to this tornado.
Sources
NWS Weather Prediction Center Surface Analysis Archive. (2017). Surface analysis 18Z Sat Sep 3 2011. Retrieved from: https://www.wpc.ncep.noaa.gov/archives/web_pages/sfc/sfc_archive.php