Tornadoes in Canada: Everything you need to know
Thursday, September 4, 2014, 12:32 PM -
More and more, Canadians are becoming aware of tornadoes and we can attribute part of that increase in knowledge and consciousness to social media. With information about severe weather at our fingertips, it has become increasingly easy for Canadians to obtain and spread knowledge of severe weather.
We tend to know a lot about tornadoes in the United States and what areas are more prone to them but, when it comes to tornadoes in Canada, the knowledge isn’t as widespread.
The following will document several items: what tornadoes are, where tornadoes occur most in Canada, some of the research being done on tornadoes in Canada, and how we can stay safe.
What Are Tornadoes?
Let’s start off with what the definition of a tornado is. The Glossary of the American Meteorological Society defines a tornado as:
A rotating column of air, in contact with the surface, pendant from a cumuliform cloud, and often visible as a funnel cloud and/or circulating debris/dust at the ground. [Updated: October 8, 2013]
This definition includes waterspouts or tornadoes that form over water but this updated definition excludes dust devils and gustnadoes which develop via a different mechanism. Tornadoes generally form out of cumuliform clouds which are the puffy white clouds in the sky (but the more violent puffy clouds called cumulonimbus, not the soft wispy ones on a nice summer day).
Tornadoes can occur with different types of storms.
The stronger, more violent tornadoes form out of supercell thunderstorms which are intense thunderstorms with a rotating updraft (rising and rotating column of air). When looking at the number of supercells that occur each year across North America, the good majority of supercells do not produce tornadoes. However, the most significant and intense tornadoes occur with supercells.
Meteorologists know the ingredients necessary to create environments conducive to tornado formation but the exact trigger, the final ingredient that ultimately kicks off ‘tornadogenesis’, is not known but there are many theories as to what it might be.
Tornadoes come in all shapes and sizes. Some are wide and menacing looking like the image below of a tornado in Goderich, Ontario. Some appear thin and wispy like the image below of a tornado near Sundre, Alberta. Do not let the way a tornado “looks” dictate to you what kind of action to take. (At the end of this there is a section on tornado safety. Be sure to give it a read.) The look of a tornado does not always dictate its strength and the amount of damage it can do. Sometimes thin tornadoes can be more violent though in a narrower path than wide tornadoes.
How Strong is a Tornado?
Tornadoes are given a rating based on the amount of damage that is done. In 1971, severe storm researcher Tetsuya (Ted) Fujita, of the University of Chicago, and Allen Pearson, then head of the National Severe Storms Forecast Center, collaborated on developing a scale that would rate tornadoes based on the damage they did to structures and vegetation.
This Fujita Scale (or F-scale) rates tornadoes on a scale of 0, being the least destructive, to 5, being the most destructive. Wind speeds ranged from 60 km/h to over 500 km/h. Based on knowledge of structural engineering, and based on a damage assessment, scientists are able to estimate the range of winds that needed to be present at the time of the tornado to cause the damage observed.
This scale was used through its creation until early 2007 in the United States and until early 2013 in Canada. In 2007, the scale was updated to the Enhanced Fujita Scale (or EF-scale) and introduced first in the United States and was adopted in Canada as of April 2013. The new EF-scale is similar to the original F-scale but with more accurate matches between wind speeds and tornado-caused damage.
Below is a chart demonstrating the old F-scale versus the Canadian implementation of the EF-scale.
Notice the lower limit on wind speeds is higher now (90 km/h instead of 60 km/h) and there is no upper limit to the strongest winds (used to be 510 km/h but now it is anything greater than 315 km/h).
Fujita and Enhanced Fujita scales as implemented by Environment Canada. Source: Environment Canada.
The main reason damage indicators are needed to rate tornado strength is that it is very difficult to make measurements of wind speed inside of a tornado.
Recently, mobile radar trucks in the United Sates, termed DOWs for Doppler on Wheels, have been able to capture velocities of tornadoes by getting near tornadoes when they are on the ground. Of course there can’t be a DOW present for every tornado that occurs so only a very small fraction of tornadoes that occur in the United States get their wind speeds measured via this method.
At this time, the official rating of a tornado is still strongly based on damage indicators rather than the DOW measured wind speeds.
NEXT PAGE: So where are Canada's twister hotspots