Alonsa, MB EF4 Tornado of August 3, 2018

Ste. Rose - McCreary - Alonsa - Gladstone

According to the Northern Tornado Project (2020), a violent EF4 tornado occurred around 8:00 pm local time and impacted the small community of Alonsa in Manitoba, leaving one fatality behind. Cars, large trucks and debris were tossed into Lake Manitoba. The damage was substantial and almost earned the rating of EF5, if it were not for the poor construction quality of the buildings impacted by this tornado.

This was the highest rated tornado in North America for the year 2018. Consenquently, it was also the first tornado rated at EF4 under the new Canadian EF-scale and the first EF4+ tornado since Elie, MB in 2007.

Post from NZP Chasers on Facebook, used with permission

The Forecast

Figure 1 depicts the surface observations at 4:00 pm CDT, which shows an occluding low pressure on the Saskatchewan/Manitoba border and a low pressure over Minot, ND. The occluded front became the focus for intense supercells in Western Manitoba, enhanced by terrain interactions and differential surface heating, which ultimately led to rapid supercellular development in the evening hours of August 3rd and resulted in an intense EF4 tornado near Alonsa.

Figure 1. Surface analysis at 21Z on August 3, 2018 showing mean sea-level pressure (MSLP) contours, surface observations, fronts and pressure centres (WPC, 2017)

According to the Northern Tornado Project (2020), an EF4 tornado touched down at 8:15 pm CDT near Alonsa, MB with maximum sustained wind speeds of 275 km/h. The tornado travelled for 15.7 km and had a maximum width of 1.2 km. One fatality and five injuries occurred as a result of this tornado. Property damage was estimated at $2 million dollars.

Figure 2. The Northern Tornado Project annual 2018-2019 report [PDF]


NWS Weather Prediction Center Surface Analysis Archive. (2017). Surface analysis 21Z Fri Aug 3 2018. Retrieved from:

Western University. (2020). The Northern Tornado Project. Retrieved from