Figure 1 shows the surface observations at 1:00 pm CDT, which shows a trough of low pressure moving east across southern Saskatchewan. This trough likely triggered thunderstorms across southwestern Manitoba in the early afternoon hours of August 11th, which ultimately led to this tornado.
According to Environment and Climate Change Canada (2018), an F1 tornado touched down at 3:30 pm CDT in Souris, MB. The track and width of the tornado was not documented by ECCC. The tornado caused no fatalities, injuries or property damage.
NWS Weather Prediction Center Surface Analysis Archive. (2017). Surface analysis 18Z Fri Aug 11 1989. 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/