So far in our look at severe summer weather, and in particular thunderstorms, we have looked at how thunderstorms form, how they can grow into severe thunderstorms, and finally, how hail is produced. Next up on the severe thunderstorm list is tornadoes! Before we begin our look at tornadoes, though, I think we have to step back a little and discuss how you can know if a storm is capable of producing severe weather, and in particular, tornadoes.
The answer is actually not that easy. The first thing is to listen to Environment Canada for watches and warnings. If a watch is issued, it means the potential exists for severe thunderstorms, but they have not yet developed in your area. When you hear there is a watch, you should watch the sky for any development, and if any storms do develop, they have the potential to become severe. If Environment Canada issues a warning, this means a thunderstorm with some or all of the characteristics of a severe storm has developed and has been confirmed by an eyewitness or radar. This means you should take precautions immediately. When conditions are favourable for severe thunderstorms and the development of tornadoes, Environment Canada will issue a tornado watch. If a tornado is either spotted by a weather spotter or indicated on radar, it will issue a tornado warning. Often, by the time a warning is issued, you will have very little time to prepare and get yourself to safety.
With all of the technology we have at our disposal nowadays, it is pretty rare to get caught without access to some kind of weather service. But, as with most things in life, it is usually when you really need something that it doesn’t work or you don’t have it with you. So, if you are out in the field without access to technology, what can you watch out for?
Heat and humidity
First of all, recognize the conditions: how warm and humid is the air? Remember, a moist atmosphere means there is a lot of energy available. Look for a dark or threatening sky; look closely at the area between the storm and the ground. If you can see through it, the storm is likely not severe yet. A lot of lightning or nearly continuous thunder is a good indication of a severe storm. As the storm approaches, keep an eye out for things such as a green sky and mammatus clouds (clouds that look like bag-like sacks that hang beneath a cloud); these conditions usually indicate the storm contains huge amounts of water and has very strong up-and-down drafts.
Another indication of a severe storm is the roll cloud. These clouds are produced ahead of an approaching storm and are caused by the cooled air flowing out of the storm. They often form a line that quickly races toward you and arrives with a strong gust of wind. Behind these clouds the sky is often a uniform dark colour.
Finally, when you are close to a storm, watch out for any kind of rotation within the storm. This means the storm has become very strong and has the capability of producing a tornado.
The word tornado for most people brings about feelings of awe and a little fear. Unless you have already witnessed a tornado first hand, many who are interested in weather often secretly wish they could safely experience the awesome beauty and power of a tornado… so long as no one get hurts and no serious property damage takes place. Unfortunately, this is rarely the case with tornadoes.
Available cold air
Worldwide, Canada is second only to the U.S. in the number of tornadoes occurring each year, with an average of about 70 reported. Southern Ontario experiences the highest number of tornadoes, followed by southern Manitoba, Saskatchewan and central Alberta. While these areas report most of Canada’s tornadoes, they have occurred in nearly all regions of Canada.
Tornadoes can strike at almost any time of the year, but in Canada, tornado season typically runs from April to October, with the peak months being June, July and August. This differs from the U.S., where tornado season peaks in April and May. This is due to the amount of cold air that is available for severe storm development. In the spring, the southern and central U.S. have become quite hot, but cold air is still closely available to help develop thunderstorms. By midsummer, most of the cold air has retreated well into Canada, putting our region into warm conditions; however, we still have cold air fairly close by to our north to help spawn severe thunderstorms.
Unfortunately, I have run out of space before we really got going into the topic of tornadoes. Next article we’ll pick up where we left off and discuss just what tornadoes are and how they form; stay tuned!