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.
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.
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