According to Environment and Climate Change Canada, “fourteen tornadoes struck several Ontario communities, namely Barrie, Grand Valley, Orangeville and Tottenham. The Barrie tornado killed eight people. In all, the family of tornadoes injured hundreds of people, destroyed or damaged over 1,000 buildings and killed 12 people, tying it with the Pine Lake, AB tornado in 2000 as the fourth deadliest tornadic day in Canada. The Grand Valley tornado that began near Arthur and moved east to Campbellford is considered one of the longest tracked tornadoes in Canada, travelling over 115 km” (ECCC, 2017).
As the Corbertoon F3 tornado was roping out, it’s respective supercell cycled up again producing another tornado just east and south of where the latter ended. This new tornado tracked almost due east for seven kilometres through a heavily wooded area. Here, it cut a swath of immense tree damage as it approached the Dufferin-Simcoe County line. Once in Simcoe County, the tornado turned slightly to the NE, uprooting more trees through the sparsely populated hamlet of Airlie. The tornado was headed straight for CFB Borden, but first passed just south of a town of Lisle, where it destroyed 2 barns and damaged a house. Luckily, the tornado lifted off as it entered the grounds of CFB Borden, where little to no damage was found.
On the morning of May 31, 1985, warm air was advecting northward across Ontario. Figure 1 depicts the surface analysis on the morning of May 31st. In Figure 1, we can see a warm front advecting northward across Ontario and a cold front moving eastward (entering Michigan). The cold front would later provide the trigger for explosive supercell thunderstorm development. According to M. Leduc, O. Jacobsen and B. Greer (1986), “the morning analysis at Environment Canada’s Ontario Weather Centre (OWC) indicated that the thermodynamic and dynamic features necessary for the possible development of severe thunderstorms were present”. As a result, severe weather watches were issued at 2:40 am local time for Southern Ontario and extended for all of Southern Ontario at 7:00 am, 9:20 am and 1:50 pm, advising the population of potential severe thunderstorm development later in the day (Leduc et al., 1986).
At 18Z (2:00 pm EDT), the cold front was entering Ontario (Figure 2). According to Leduc et al. (1986), an unseasonably strong low pressure centre tracked across Northern Michigan during the morning hours to just north of Sudbury by evening. The visible satellite loop below shows the development and explosive growth of thunderstorms across Southern Ontario, Ohio, Western Pennsylvania and Western New York on the afternoon of May 31st.
At 21Z (5:00 pm EDT), the cold front was in Western Ontario (Figure 4).
Leduc et al. (1986) notes that the dynamics in place were strong since a sharp cold front (Figure 1, 2 and 4) and an upper trough was crossing Michigan, bringing with it strong westerlies in the upper-levels of the atmosphere.
Figure 5 and 6 depict the radar imagery from the King City radar (north of Toronto). At 1:40 pm (local time), radar showed the first thunderstorms developing west and north of the Bruce Peninsula. By 2:20 pm, a line of severe storms was indicated by radar (Figure 5). The first severe thunderstorm warning was issued at 2:25 pm for the Bruce County and Parry Sound District. At 3:15 pm, severe thunderstorm warnings were issued for Huron, Perth, Grey, Northern Wellington and Northern Waterloo Counties, with the most intense storms being seen from Meaford to Perth County (Leduc et al., 1986). At 4:00 pm, reports of 2 cm hail and very high winds were received at the OWC for the Meaford and Dundalk area. Around 4:00 pm, radar showed a line of severe storms extending from Collingwood to Eastern Perth County moving east at 60-70 km/h (Figure 6).
Between 4:20 pm and 4:40 pm, radar showed signs that the southern storms off the squall line were intensifying and therefore warnings were issued at 4:53 pm from Hamilton-Wentworth to Durham and Victoria counties. A tornado warning was issued at 5:00 pm for Southern Simcoe, Northern Peel and York counties after OWC received reports of a tornado at 5:00 pm and 5:20 pm. At 5:50 pm severe thunderstorm warnings were issued for the Niagara Peninsula. Tornado warnings were extended for Southern Durham and Peterborough counties at 6:05 pm and Haliburton, Northumberland, Prince Edward and Hastings counties at 6:25 pm. At 7:00 pm, warnings/watches were cancelled for all regions, except for Haliburton County and east of Oshawa where tornado reports southwest of Peterborough and Rawden Township were received between 6:40 pm and 7:20 pm. A timeline of tornado occurrence, severe thunderstorm warnings and tornado warnings are presented in Table 1 below.
According to ECCC (2018), the Lisle F2 tornado touched down at 4:50 pm local time near Lisle, ON and tracked for 12.1 km, moving in a east-northeasterly direction and ending just east of the town of Lisle. The maximum width of the tornado was not documented. ECCC (2018) did not catalogue any injuries, fatalities or damage associated with this tornado.
Environment and Climate Change Canada (2017). Top Weather Events of the 20th Century. Retrieved from: https://ec.gc.ca/meteo-weather/default.asp?lang=En&n=6A4A3AC5-1#tab5
NWS Weather Prediction Center (2017). North American Surface Analysis: Surface Analysis 12Z Friday May 31, 1985. Retrieved from: https://www.wpc.ncep.noaa.gov/html/sfc2.shtml
National Weather Service (2019). May 31, 1985 Tornado Outbreak: 34th Anniversary. Retrieved from: https://www.weather.gov/ctp/TornadoOutbreak_May311985#Meteorology
M. Leduc, O. Jacobsen and B. Greer (Winter 1986). The “Black Friday” Tornado Outbreak in Ontario. Chinook, 8, 13-18. Retrieved from: cmosarchives.ca/Chinook/ch0801.pdf
The Weather Network (2019). Massive Ontario tornado outbreak marks anniversary. Retrieved from: https://www.theweathernetwork.com/ca/news/article/anniversary-of-the-barrie-tornado-grand-valley-tottenham-may-31-1985-tornado-outbreak
Environment and Climate Change Canada (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/?lang=en