Figure 1 shows the surface observations at 10:00 pm CDT, which shows a cold front moving through the City of Winnipeg. This cold front triggered thunderstorms, which ultimately led to this brief tornado in Winnipeg.

According to Environment and Climate Change Canada (2018), an F0 tornado touched down at 10:23 pm CDT in the City of Winnipeg, MB. The track and width of the tornado was not documented by ECCC. The tornado caused no fatalities, injuries or property damage.
Sources
NWS Weather Prediction Center Surface Analysis Archive. (2017). Surface analysis 03Z Sun May 8 1988. 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/