Figure 1 shows the surface observations at 7:00 am CDT, which shows a cold front moving across southern Manitoba. We are unsure at this time how a storm could have developed from this setup. It is possible that a lake-breeze developed from Lake Manitoba behind the cold front, which combined with surface heating around Morden could have triggered thunderstorms.
According to Environment and Climate Change Canada (2018), an F0 tornado touched down at 5:00 pm CDT near Morden, MB. The track and width of this tornado was not documented by ECCC. The tornado caused no injuries, fatalities or property damage.
Sources
NOAA Central Library. (2020). U.S. Daily Weather Maps. Wednesday May 28, 1980 [PDF]. Retrieved from https://library.noaa.gov/Collections/Digital-Collections/US-Daily-Weather-Maps
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/