When weather becomes dangerous
Most days, weather is just something we dress for. But sometimes it becomes severe weather, dangerous enough to damage property, injure people or even take lives. Canada experiences almost every kind of severe weather, from blizzards to tornadoes to heat waves.
Thunderstorms
A thunderstorm forms when warm, moist air rises quickly into cooler air, building towering cumulonimbus clouds.
Lightning
Lightning is a giant electric spark. Inside storm clouds, ice and water particles collide and build up electric charges. When the charge is big enough, it jumps between clouds or to the ground.
- A lightning bolt can heat the air to about 30 000 °C, five times hotter than the Sun’s surface.
- The heated air expands so fast it creates the boom of thunder.
- Canada gets about 2.3 million lightning flashes a year.
Safety: "When thunder roars, go indoors." If you can hear thunder, you’re close enough to be struck. Wait 30 minutes after the last thunder before going outside. Avoid open fields, tall trees, water and metal fences.
Hail
Hail forms when strong updrafts carry raindrops up into freezing parts of a cloud again and again, adding layers of ice. Canada’s largest recorded hailstone fell in Didsbury, Alberta, in 2022: about 12.5 cm across, roughly the size of a grapefruit. Alberta’s "Hailstorm Alley" between Calgary and Red Deer is one of the most hail-prone areas in the world.
Tornadoes
A tornado is a violently spinning column of air reaching from a thunderstorm to the ground. Canada averages about 60 confirmed tornadoes a year, more than any country except the United States. (See the Tornadoes lesson for more.)
Hurricanes
Hurricanes are huge spinning storms that form over warm oceans. They can bring damaging winds, flooding rain and storm surges to Atlantic Canada. In 2022, post-tropical storm Fiona became one of the most costly storms in Atlantic Canada’s history.
Winter storms
| Storm | What happens |
|---|---|
| Blizzard | Strong winds (at least 40 km/h) with blowing snow, making visibility less than 400 m for several hours |
| Ice storm | Freezing rain coats everything in ice, snapping trees and power lines |
| Extreme cold | Very low temperatures with wind chill can cause frostbite in minutes |
The 1998 ice storm left millions of people in Ontario, Quebec and New Brunswick without power, some for weeks.
Wind chill
Wind makes cold air feel colder by carrying heat away from your skin. At a temperature of −20 °C with a 30 km/h wind, it feels like about −33 °C. Exposed skin can freeze in 10–30 minutes.
Heat waves
A heat wave is a period of unusually hot weather lasting several days. They can be deadly, especially for older adults, babies and people with health conditions.
In late June 2021, a "heat dome" brought record temperatures to Western Canada. Lytton, BC, reached 49.6 °C, Canada’s highest temperature ever recorded. Hundreds of people died in BC, and the next day a wildfire destroyed most of the village.
Safety: drink lots of water, stay in the shade or air conditioning, and check on neighbours.
Floods
A flood happens when water overflows onto normally dry land.
| Cause | Example |
|---|---|
| Heavy rain | 2013 Calgary flood |
| Spring snowmelt | Red River floods in Manitoba |
| Ice jams on rivers | Many northern rivers in spring |
| Storm surges | Coastal flooding during hurricanes |
| Atmospheric rivers | 2021 BC floods that cut off Vancouver by road |
Never walk or drive through floodwater. Just 15 cm of moving water can knock you down, and 60 cm can float a car.
Drought and wildfires
A drought is a long period with little rain. Dry conditions increase the risk of wildfires. In 2023, Canada had its worst wildfire season on record, burning more than 15 million hectares and filling skies with smoke across North America.
Weather warnings
Environment and Climate Change Canada issues alerts:
| Alert | Meaning |
|---|---|
| Special weather statement | Unusual weather that may be a concern |
| Advisory | Weather that may cause inconvenience |
| Watch | Conditions are favourable for severe weather; be prepared |
| Weather warning | Severe weather is happening or about to happen; take action |
Alerts are sent through the WeatherCAN app, radio, TV and the Alert Ready system on cell phones.
Be prepared
Every household should have an emergency kit with:
- water (about 4 L per person per day for at least 3 days)
- non-perishable food
- flashlight and batteries
- first-aid kit
- medications
- a battery-powered or crank radio
- warm clothing and blankets
Common mistakes
- Thinking lightning never strikes the same place twice. Tall buildings are struck many times a year.
- Thinking it’s safe to shelter under a tree in a storm.
- Thinking a "watch" means the same as a "warning."
Try it yourself
- Count the seconds between lightning and thunder and divide by 3 to estimate the distance in kilometres.
- Make a family emergency kit checklist.
- Research a severe weather event that affected your province. What caused it and how did people respond?
Quick recap
- Severe weather includes thunderstorms, tornadoes, hurricanes, blizzards, heat waves and floods.
- Lightning is a giant electric spark; go indoors when thunder roars.
- Canada experiences extreme cold, heat, hail, floods and wildfires.
- Watches mean be prepared; warnings mean take action.
- Emergency kits and plans help keep families safe.