Nature’s most violent winds
A tornado is a violently rotating column of air that stretches from a thunderstorm down to the ground. Tornadoes produce the fastest winds on Earth’s surface, sometimes over 300 km/h. Most last only a few minutes, but they can destroy everything in their path.
How tornadoes form
Most strong tornadoes come from supercells, powerful thunderstorms with a rotating updraft.
- Wind shear: winds near the ground blow from one direction, while winds higher up blow faster or from a different direction. This creates a horizontal rolling tube of air.
- Tilting: a strong thunderstorm updraft tilts the rolling air upright, creating a rotating column called a mesocyclone.
- Stretching: the rotation narrows and speeds up, like a figure skater pulling in her arms.
- Touchdown: a funnel cloud may lower from the storm. When it touches the ground, it becomes a tornado.
Scientists still don’t fully understand why some supercells make tornadoes and others don’t.
What tornadoes look like
- Many look like a funnel or rope; others are wide wedges.
- They’re often hidden by rain or darkness.
- Debris and dust swirl around the base.
- Some sound like a freight train or a loud roar.
Warning signs: a dark, greenish sky, large hail, a low, rotating wall cloud, and a loud roar.
Measuring tornadoes
Tornadoes are rated after they happen, by studying the damage, using the Enhanced Fujita scale. Canada adopted its own version in 2013.
| Rating | Estimated wind speed (km/h) | Damage |
|---|---|---|
| EF0 | 90–130 | Light: shingles and branches |
| EF1 | 135–175 | Moderate: roofs damaged, mobile homes overturned |
| EF2 | 180–220 | Considerable: roofs torn off, large trees snapped |
| EF3 | 225–265 | Severe: walls collapse, trains overturned |
| EF4 | 270–310 | Devastating: well-built houses levelled |
| EF5 | Over 315 | Incredible: homes swept away |
About 75% of tornadoes are weak (EF0 or EF1). Only a tiny fraction are EF4 or EF5, but they cause most of the deaths.
Where tornadoes happen
The United States has more tornadoes than any other country, more than 1000 a year, especially in "Tornado Alley" in the central plains.
Canada has the second most, averaging about 60 confirmed tornadoes each year, though many more likely go unreported in remote areas. The Northern Tornadoes Project, based at Western University in London, Ontario, has found many previously missed tornadoes by studying satellite images of forests.
| Region | Notes |
|---|---|
| Southern Ontario | Among the most tornadoes in Canada |
| Southern Quebec | Frequent tornadoes |
| Prairies (Alberta, Saskatchewan, Manitoba) | Many tornadoes in open land |
Tornado season in Canada is mainly June to August, though they can happen from spring to fall.
Notable Canadian tornadoes
| Tornado | Year | Rating |
|---|---|---|
| Regina, SK ("Regina Cyclone") | 1912 | Killed 28; Canada’s deadliest |
| Edmonton, AB ("Black Friday") | 1987 | F4; killed 27 |
| Elie, MB | 2007 | F5; Canada’s only officially confirmed F5 |
| Ottawa–Gatineau | 2018 | EF3; damaged hundreds of homes |
| Barrie, ON | 2021 | EF2 |
Tornado safety
Environment and Climate Change Canada issues alerts:
| Alert | Meaning | What to do |
|---|---|---|
| Tornado watch | Conditions are right for tornadoes | Stay alert; know where you’ll take shelter |
| Tornado warning | A tornado is happening or about to | Take shelter immediately |
Where to shelter
- Best: a basement or storm shelter. Get under a sturdy table or stairs.
- No basement: go to a small room on the lowest floor, in the middle of the building, away from windows (a bathroom, closet or hallway).
- Cover your head and neck with your arms, a mattress or blankets.
- Mobile homes and cars are not safe. Go to a sturdy building.
- If caught outside, lie flat in a ditch or low area and protect your head. Don’t shelter under an overpass.
Common mistakes
- Thinking you should open windows to "equalize pressure." It wastes time and doesn’t help.
- Thinking tornadoes don’t happen in Canada.
- Thinking big cities or rivers protect against tornadoes. They don’t.
Try it yourself
- Make a "tornado in a bottle": connect two plastic bottles (one with water) neck-to-neck with tape or a connector. Swirl and flip.
- Plan the safest tornado shelter spot in your home and school.
- Compare tornadoes and hurricanes in a chart: size, duration, where they form and wind speeds.
Quick recap
- Tornadoes are rotating columns of air from thunderstorms to the ground.
- Most strong tornadoes come from supercells with rotating updrafts.
- They’re rated EF0 to EF5 by damage.
- Canada has the second-most tornadoes in the world.
- In a tornado warning, go to a basement or interior room on the lowest floor.