Grand Valley, ON F1 Tornado of July 1, 1999

Dufferin - Innisfil

This tornado touched down at 5:55 pm, tearing the roofs and siding off of two barns. Debris was scattered throughout farm fields and a cattle truck was flipped over. Witnesses described the tornado as a white cone that was fully condensed to the ground.

This was one of two tornadoes to touch down in Southern Ontario on July 1; the other was an F1 near Wingham.

Figure 1 depicts the surface observations at 2:00 pm, which depicts a low pressure system in Michigan with a warm front extending into southern Ontario. As this front lifted north, it became the focus for intense thunderstorms, which led to this F1 tornado.

Figure 1. Surface analysis at 18Z on July 1, 1999 showing mean sea-level pressure (MSLP) contours, surface observations, fronts and pressure centres (WPC, 2017)

According to Environment and Climate Change Canada (2018), an F1 tornado touched down at 5:55 pm EDT near Grand Valley, ON. The path 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 Thu Jul 1 1999. Retrieved from:

Environment and Climate Change Canada Data. (2018). Canadian National Tornado Database: Verified Events (1980-2009) – Public. Retrieved from: