The outbreak spawned several long-lived, cyclic, tornado-producing supercells over portions of Eastern Canada and the Great Lakes region of the Midwestern and Northeastern United States, one of which eventually generated the Barrie tornado.

On the afternoon of May 31, 1985, atmospheric conditions were conducive to a large-scale severe weather event over portions of the Great Lakes region.

Severe thunderstorms and isolated tornadoes had already impacted portions of the Midwest, particularly Iowa and Wisconsin, the day previous, associated with this same cold front.

[1][2][3] Over Ontario two very severe thunderstorms had developed (that probably owe their inception, at least partially, to lake-breeze-related convergence): one to the east of Clinton and another further to the north, in the Walkerton area.

[5] It formed in southern Simcoe County (Essa Township), less than 10 kilometres (6.2 mi) southwest of Highway 400 and the Barrie city limits.

The situation was compounded by the presence of copious amounts of moisture, which would not only allow any storms that could form to become severe rather quickly, but also lead to the high-precipitation (HP) counterpart of the supercell thunderstorm, obscuring any tornado that could manage to develop.

Extensive F3 (although some localized F4) damage occurred to an entire square block of homes in the Crawford Street and Patterson Road subdivision.

[7] Most of the fatalities occurred in homes with no basements, where head and chest trauma resulted from an increased exposure to flying debris.

[7] Several vehicles traveling on Highway 400 were tossed hundreds of metres into the ditch, the drivers escaping with only minor injuries.

Despite the tornado's relatively short path length (under 10 kilometres (6.2 mi)), eight died in Barrie with 155 injured, and as many as 300 homes were damaged or destroyed.

[5] Hundreds of people were left out of work largely as a result of the massive damage sustained to the industrial complex in Barrie.