Severe Weather: Tornadoes

The Weather Vane is prepared by Daniel Bezte, a teacher by profession with a B. A. (Hon.) in geography, specializing in climatology, from the University of Winnipeg. Daniel has taught university-level classes in climate and weather and currently operates a computerized weather station at his home near Birds Hill Park, on 10 acres he plans to develop into a vegetable and fruit hobby farm.

Contact him with your questions and comments at [email protected]

While western Manitoba did see some thunderstorms earlier this month, overall, the start of the thunderstorm season across North America has been very quiet – at least until last weekend. The reason for this quiet start is the continuation of warm weather over Canada and colder-than-average temperatures over the southern states. This means the key ingredients for thunderstorms (i. e., a big difference in temperatures) just haven’t been there this year.

In fact, the outbreak of severe weather over the southern states last weekend was the latest the first outbreak of severe weather has ever occurred. Previously, the latest in the year a severe outbreak of thunderstorms occurred was around March 24, so this year was a full month later.

I did say a couple of weeks ago I would take a look this week at how hail is produced in thunderstorms, but I think with the killer tornadoes occurring in the southern U. S., that topic will have to wait a little bit. Instead we’ll go back to the original plan and look at tornadoes. Before we begin our look at tornadoes I think we have to step back a little bit and discuss: how can you know if a storm is producing severe weather?


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 by EC it means that the potential exists for severe thunderstorms, but they haven’t 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 EC issues a warning, this means that a thunderstorm with some or all of the characteristics of a severe storm has developed and has been confirmed by eyewitnesses or radar. This means you should take precautions immediately.

If you’re out in the field without access to a radio, what can you watch out for?

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. Lots of lightning or nearly continuous thunder is a good indication of a severe storm. As the storm approaches, keep an eye out for such things as a green sky and mammatus clouds (clouds that look like bag-like sacks that hang beneath a cloud); these conditions usually indicate that the storm contains huge amounts of water and has very strong up and down drafts. Finally, 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 a feeling of awe and even a little fear. Unless you have already witnessed a tornado first hand, many who are interested in weather secretly wish they could safely experience the awesome beauty and power of a tornado.

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 any time of the year, but in Canada, tornado season runs from April to October, with the peak months being June, July and August. This differs from the U. S., where tornadoes peak in April and May. This is due to the amount of cold air available for severe storm development. In the spring, the southern and central U. S. has 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.

Unfortunately I’m starting to run out of space before we really got going into the topic of tornadoes. Next week we will do our monthly look back at April’s weather and then look ahead to see if our above-average weather will continue, or will it be time to pay back Mother Nature for all the extra warm weather we have been experiencing? Then, barring any really unusual weather, we will pick up where we left off and discuss just what tornadoes are and how they form. Stay tuned!

About the author

Co-operator contributor

Daniel Bezte

Daniel Bezte is a teacher by profession with a BA (Hon.) in geography, specializing in climatology, from the U of W. He operates a computerized weather station near Birds Hill Park.



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