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Tornadoes in Canada: Everything you need to know

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Dayna Vettese
Meteorologist

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). 

A maturing cumulonimbus cloud.

A maturing cumulonimbus cloud.

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.  

Tornado in Goderich, Ont., August 23, 2011

Tornado in Goderich, Ont., August 23, 2011

Tornado near Sundre, Alta., July 7, 2011

Tornado near Sundre, Alta., July 7, 2011

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.

Tornado near Elie, Man., on June 22, 2007, Canada's only verified F5 tornado.

Tornado near Elie, Man., on June 22, 2007, Canada's only verified F5 tornado.

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

Where Do Tornadoes Occur in Canada?

Tornado Alley: a region of the United States where we find the highest frequency of tornadoes. This is a widely known fact. When you mention Kansas you can’t help but remember the infamous scene from the Wizard of Oz. If you mention Oklahoma, you can’t help but recall the devastating tornadoes that have torn through Moore, Oklahoma on several occasions. 

But, generally speaking, when you mention tornadoes in Canada, we don’t get a clear cut image of where the tornado-prone zones are in our vast country. 

Dr. David Sills, a severe weather scientist and tornado guru, undertook a project to update the national tornado database for Canada with several colleagues and research assistants. Sills explains: “Environment Canada research on tornadoes is related to developing new climatological data based on verified tornadoes, and investigating statistical approaches that adjust observed tornado data in order to compensate for population bias.” 

They scoured through endless records, newspaper clippings, files, videos, pictures and firsthand accounts to reanalyze tornadoes that were in the database, update their ratings and add any missing tornadoes. There was no central tornado database across Canada as it was split amongst the various regions of Canada (Prairies, Ontario, etc). Upon building this database, Sills and his team were able to come up with a country-wide average of tornadoes each year as well as per province.

Tornadoes per year per province and nationally. Source: *Ongoing* research, Environment Canada (Sills et al).

As shown in the image above, on average, Canada gets 62 verified tornadoes per year. Saskatchewan has the highest per province with about 18 tornadoes, followed by Alberta with an average of 15 tornadoes then Ontario with an average of 12-13 tornadoes each year. 

Sills et al. also reviewed the seasonal variation of tornadoes across Canada and found that the months with the most number of tornadoes was July. There is a sharp rise in activity from April to May then a decline into October with July peaking in activity in the middle. In studying the tornadoes in the database, they were also able to determine that most tornadoes (but not all) occurred between 1:00pm and 8:00pm local time. 

The team was able to map every confirmed or probable tornado from 1980 through 2009 as shown below.

Confirmed and probable tornadoes across Canada from 1980-2009. Note Canada's only F5 tornado occurred in Manitoba. Source: Sills et al., 2012

Assessing where tornadoes occur in Canada is a lot more difficult than one may think and this has a lot to do with population density. 

We know, as meteorologists, that a great deal of thunderstorm activity occurs in northern regions of the Canadian Prairies, northern Ontario and western Quebec. Due to the lack of population in those areas there is an obvious data hole because there just aren’t people there to see or report tornadoes or tornado damage. Sometimes helicopters flying over the area may notice damage paths that would have otherwise gone unnoticed such as in the vast forested regions of northern Ontario. 

In the image above, there is a noticeable gap especially in parts of northern Ontario. Sills and his team applied a method to help fill in these data gaps to get a better outline of tornado prone areas in Canada. 

“There are some rural and/or remote areas of Canada where we get very little in the way of tornado reports, but we know that intense thunderstorms capable of producing tornadoes regularly occur there,” explains Sills. “A new dataset that we have at our disposal is lightning activity across Canada. We now have a ten year dataset with many millions of lightning flashes.” 

They used this dataset to help model tornado incidence. They combined this lightning flash density climatology with a population density mask. This helped them to correct for population bias. For example, a great number of people would report a tornado if it occurred near the Greater Toronto Area where maybe only a couple of people would report a tornado in a rural area north of Regina compared to no one reporting a tornado that occurred in the forests of northern Ontario. 

This modelling technique resulted in a preliminary value of 230 tornadoes across Canada each year! The team also has to apply some more algorithms to account for F-scales.

To outline tornado prone areas, first they needed to plot all the confirmed and probably tornadoes on record. Sills and his team had to define the outlining regions (Source: Sills et al. 2012)

Prone to Significant Tornadoes – Probability of an F2 – F5 tornado is estimated to exceed 10-5/km2/year. F0 – F1 tornadoes will be more frequent. 

Prone to Tornadoes – Probability of an F0 – F1 tornado is estimated to exceed 10-5/km2/year.

Tornadoes Observed – Rare – Tornadoes observed, but probability of a tornado is between 10-5/km2/year and 10-6/km2/year.

Based on these findings, a tornado-prone map was created and then published in the National Building Code – 2011. Below is the map outlining the tornado-prone areas in Canada.

Tornado prone areas in Canada as published to the National Building Code, 2011, based on research from Environment Canada.  Source: Adapted from Sills et al., 2012.

When asked what he would consider to be Canada’s “Tornado Alley” based on the findings of his research, Sills mentions two main areas: “One is the southern Prairie provinces, and the other is southern Ontario into southern Quebec. Within those areas, southern Saskatchewan and Manitoba – south of a line from roughly Saskatoon to Winnipeg – and the part of southern Ontario between the Great Lakes from roughly Windsor to Barrie are the two most active tornado corridors [in Canada].” 

Another interesting outcome of the research was that these results, the mapped tornado-prone areas, have activated certain measures in the National Building Code of Canada. What this means for Canadians is more tornado-resilient construction on new homes in the at-risk regions.

For the weather-savvy individual, this might not come as a huge surprise but it is clear that tornadoes are a real threat to many Canadians. When asked what one of the biggest revelations was upon working on this research, Sills mentions that it was interesting and impressive to him that 

“The number of tornadoes we verify each year (62 on overage) is only a fraction of what actually occurs – perhaps only about quarter," explains Sills.

Tornado-related research has also been undertaken in the science of structural engineering. 

“We also worked with wind engineers at Western University in London to increase our knowledge of the relationships between wind damage and wind speed, to be used to improve the Enhanced Fujita Scale for wind damage rating,” Sills describes. 

Tornado Safety

So as summer severe weather season approaches for Canadians, we want to keep you prepared. Tornadoes are not a guarantee but as the research shows, they are a clear threat to many Canadians and it is important to know your tornado safety tips. 

It is also important to have a plan in place and know where your safe spot is or what to do should you be faced with a tornado threat. 

I asked Dr. Sills to give me an important safety fact about tornadoes that many Canadians might not know. His response was: “If tornado winds get inside your home or garage, it becomes much easier for the tornado to remove the roof and even the walls. So when Environment Canada issues a tornado watch [or threatening weather approaches], make sure to close all windows and doors, including garage doors, and secure objects that could become missiles and break windows, such as lawn furniture [should you have time to do so].” 

The Weather Network tracks severe weather 24 hours a day, seven days a week. We will track the storms, forecast the risk of severe weather and broadcast all watches and warnings issued by Environment Canada. A great way to stay weather aware is to know your forecast for the day. If you’re heading out for a day trip or maybe planning a camping trick, know your forecast. 

For more tornado safety tips, please visit: http://www.theweathernetwork.com/news/articles/tornado-safety-tips/9366/

Tornadoes: Fact or Fiction

FICTION: Objects such as rivers, lakes or mountains can protect certain areas from tornadoes.

FACT: No geographical location is safe from tornadoes. Though there are areas more prone to tornadoes, they can occur almost anywhere.

FICTION: Opening up windows before a tornado approaches will equalize the pressure in your structure minimizing the damage.

FACT: Opening the windows can actually make your house more vulnerable during a tornado. Do not take the time to open windows but seek shelter immediately. Underground, basement or interior room will be the safest places with as many walls between yourself and the outside as possible (preferably windowless).

FICTION: Sheltering under a highway overpass will keep you safe from tornadoes.

FACT: Overpasses are particularly dangerous during tornadoes as debris can get caught in the area and wind speeds increase through the narrow openings. In you are in your vehicle when a tornado approaches, as a last resort, you can stay in your vehicle with your seatbelt on and your head down. If you see a noticeably lower area in terrain, get out of your vehicle and lie flat in that area with your arms protecting your head.

References

Sills, D., V. Cheng, P. McCarthy, B. Rousseau, J. Waller, L. Elliott, J. Klaassen and H. Auld, 2012: Using tornado, lightning and population data to identify tornado prone areas in Canada. Preprints, 26th AMS Conference on Severe Local Storms, Nashville, TN, Amer. Meteorol. Soc., Paper P59


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