Weatherbee

Check your local conditions and know your weather definitions. Please take a moment to download this information. It may save your life..


TORNADO

If we lived in a perfect world we would all receive ample warning that a tornado was approaching. Even with all of today's technology in weather forecasting it is difficult to give much lead time when it comes to tornadoes.

Let us suppose Environment Canada issued a tornado warning with a lead time of two hours on a Monday afternoon at 2 o'clock. Most people would be at work and children at School. Even with such a lead time unless you were aware of the warning you would not be able to take the necessary safty precautions. Is therefore, the onus on the public, to be weatherwise and to be able to recognise the signs of impending weather?

The following information provided by Environment Canada, is to help you play and work safe over the summer months.

The typical tornado first appears as a rotation in a huge thunder cloud behind a shroud of heavy rain or hail. The sky turns green or yellow or black as night. Then it descends, a violently twisting funnel cloud. It rumbles like a freight train or screeches like a jet, Iouder and louder, until the sound is deafening. Snaking erratically from southwest to northeast, the twister topples buildings, scatters debris and tosses cars as though they were toys. Gone minutes later, the tornado leaves a wake of destruction. Hopefully, you had taken all neccessary precautions before all this occurred.

In Canada, during an average year, 80 tornadoes cause two deaths and 20 injuries, plus tens of millions of dollars in property damage. These are the reported numbers--who knows how many more tornadoes strike unpopulated areas undetected.

The picture was taken in Amaranth township by Darlene Frizzell and shows the 1996 tornado that struck Violet Hill.

The averages are also deceiving because the majority of twisters do little more than bend TVantennae, break windows, uproot trees, or damage weak structures such as barns and sheds. With wind speeds of less than 160 km/h, and a path 100 m wide by 2 km long, these small tornadoes cause less than three percent of deaths.

It's the strong tornadoes every few years in Canada that cause the most destruction. With winds of 300 km/h, and a path 15 km long by 200 m wide, these twisters cause 97 percent of all deaths.

The worst tornadoes are the most violent storms on earth. With winds approaching 500 km/h, they can level even the most solid structures. The path of destruction can reach 42 km long and 390 m wide. Fortunately, Canada has never seen such a storm.

Incidentally, the odds of dying from a tornado are 12 million to one.

Just as the Richter scale measures the intensity of earthquakes, the Fujita scale measures tornado strength. F0 is the least intense; F5, the most intense. The scale is named for Dr. T. Fujita, a pioneer in tornado research at the University of Chicago.

The tornado typically moves over the ground at speeds between 20 and 90 km/h. The path is usually southwest to northeast, although it can be erratic and may change direction suddenly.

If you see a tornado and it does not appear to be moving, it is either moving straight away or straight toward you.

Canada's "tornado alleys" are southern Ontario, Alberta, southeastern Quebec, and a band stretching from southern Saskatchewan and Manitoba through to Thunder Bay. The interior of British Columbia and western New Brunswick are also tornado zones.

May to September are the prime tornado months, with the peak season in June and early July. The afternoon and early evening are the peak times. Twisters are rare in winter.

Tornadoes' precursors are warm humid weather and thunderstorms that develop when cool northern air masses collide with hot air flowing north from the Gulf of Mexico. Throw in a complicated pattern of updrafts and downdrafts in the atmosphere, and part of the base of the thunder cloud starts to rotate. A tornado is born.

While most tornadoes look like a violently twisting funnel cloud, some may look more like a large, low-lying cloud, a large rain shaft or even smoke from a fire. The shape can change before your eyes!

Exceptionally large thunderstorms can spawn multiple tornadoes, or a single tornado made up of a number of smaller but intense vortices rotating about a common centre.

Experts aren't sure why the centre of one thunder cloud will spin and another one won't. To better understand the dynamics, researchers at Environment Canada are studying images of actual tornado clouds from radar, satellites and photographs. This research will lead to more accurate forecasts and more timely warnings.


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