Figure 1 depicts the surface analysis at 5:00 pm EDT, showing a significant occluding low pressure system over Wisconsin. A warm front is extending across the Great Lakes and through southern Ontario. This front became the focus for thunderstorm development in the late afternoon and evening hours. Lake-breeze interactions from Georgian Bay may have also played a roll in initiating storms and storm intensification for this F0 tornado to develop.
According to Environment and Climate Change Canada (2018), an F0 tornado touched down at 7:55 pm EDT near Underwood, ON. The track and width of the tornado was not documented by ECCC. The tornado caused no injuries, fatalities or property damage.
NWS Weather Prediction Center Surface Analysis Archive. (2017). Surface analysis 21Z Wed Jul 3 1991. Retrieved from: https://www.wpc.ncep.noaa.gov/archives/web_pages/sfc/sfc_archive.php
Environment and Climate Change Canada Data. (2018). Canadian National Tornado Database: Verified Events (1980-2009) – Public. Retrieved from: http://donnees.ec.gc.ca/data/weather/products/canadian-national-tornado-database-verified-events-1980-2009-public/