On 18 April 2013, a short-lived tornado moved through the Shelburne area of Ontario, northwest of Toronto. It touched down about 6 km (3.8 miles) from town at approximately 5:45 pm EDT, bringing damage to a barn. Investigators from Environment Canada determined that the storm path was 10 km long (6.25 miles) and 75 m (246 ft) wide. Based on the damage done to the barn, the assessment team rated the tornado as a level 1 on the Canadian Enhanced Fujita Scale (EF-Scale).
This tornado was the first of the 2013 tornado season in both Ontario and Canada, and as such became a historic storm. Not for its damage, but for the fact that it was the first tornado every rated on the Enhanced Fujita Scale, denoted by Efx, where x is the rating level. Although the United States introduced the Enhanced Fujita Scale in 2007, Canada had continued using the older Fujita Scale over the last six years.
The reason for the delay according to Environment Canada was that they felt that the winds associated with the storm's damage weren’t very well correlated and needed more engineering studies of wind speed and damage. A study conducted in 2012 of assessments using the two scales, found the narrower ranges of the EF-Scale to be more indicative of the actual wind speeds, especially for strong and violent tornadoes.
An estimate of wind speeds present during a tornado of each particular Canadian EF-rating is:
Canada Enhanced Fujita Scale Ratings: (Rounded to nearest 5 km/h)
EF0 - Winds of 90-130 km/h
EF1 - Winds of 135-175 km/h
EF2 - Winds of 180-220 km/h
EF3 - Winds of 225-265 km/h
EF4 - Winds of 270-310 km/h
EF5 - Winds of 315 km/h or greater
Wind speed ranges for the old Fujita Scale and the enhanced scale are not strictly convertible as say, Fahrenheit to Celsius temperature scales would be. Therefore, the two will be distinguished in the historic record by the use of Fx and EFx for the old Fujita Scale and Enhanced Fujita Scale, respectively, where x denotes the scale level. Though F-scale and EF-scale wind speeds are different, both still have the same damage scales. Hence, ratings based on damage will be the same for older events rated with the F-scale and newer events rated with the EF-scale (Sills, 2013).
Written by Keith C. Heidorn, PhD, THE WEATHER DOCTOR,
May 1, 2013; revised 28 May 2013. My thanks to David Sills for his comments on the original essay.
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