A thin tornado was spotted by witnesses as trees were damaged and debris thrown short distances. This was one of three tornado that touched down in Southern Ontario on June 23.
Figure 1 depicts the surface observations at 5:00 pm EDT, which shows a warm front across Michigan and entering Ontario. This front moved into southwestern Ontario throughout the evening hours of June 23rd and with the help of an outflow boundary (observed at 15Z south of Midland), initiated intense thunderstorms, which ultimately led to a long-track F2 tornado in Midland and a long-track F1 tornado that ended in Washago.
Sources
NWS Weather Prediction Center Surface Analysis Archive. (2017). Surface analysis 21Z Wed Jun 23 2010. Retrieved from: https://www.wpc.ncep.noaa.gov/archives/web_pages/sfc/sfc_archive.php