Newmarket, ON F1 Tornado of August 20, 2009

York - Durham

The F1 tornado at Newmarket, Ontario. This tornado formed just to the east of Newmarket at 5:50pm and had a path that was 2.5km long. Witnesses captured video of it, a slender elephant trunk with a plume of debris at its base, as it tore through a rural area just outside of town.

The Royal Canadian Riding Academy sustained considerable damage with the roofs partially torn from barns and stables, trailers tossed, fences knocked down and debris strewn across the property. Fortunately there were no injuries to people or horses at the Academy, although two riders were particularly fortunate to have escaped unharmed when they sought shelter in horse trailers which were tossed.

This was one of nineteen tornadoes that struck Southern and Central Ontario on August 20. Figure 1 depicts a line of severe thunderstorms entering southwestern Ontario from Michigan. These thunderstorms were responsible for the tornado outbreak on this day.

Figure 1. Doppler radar imagery at 3:38 pm EDT on August 20, 2009 (Source: Meteologix)

Figure 2 depicts the surface observations at 5:00 pm EDT, which shows a cold front moving through the Great Lakes and a warm front in central Ontario. The warm sector (southern Ontario), brought southerly winds moving across the open waters of Lake Ontario and Lake Erie. The advancing cold front and possible interactions with lake-breeze boundaries developed pre-frontal storms across southwestern Ontario, which moved east and brought one of the most significant tornado outbreak in Ontario’s history.

Figure 2. Surface analysis at 21Z on August 20, 2009 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 5:50 pm near Newmarket, ON. The tornado travelled for 2.47 km and had a maximum width of 300 metres. The tornado caused no fatalities, injuries or property damage.


NWS Weather Prediction Center Surface Analysis Archive. (2017). Surface analysis 21Z Thu Aug 20 2009. Retrieved from:

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