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Thunderstorms, blizzards, high winds and heavy rain can develop quickly and hit hard, threatening life and property. Severe weather can occur any time of the year. Make it a habit to listen to the local radio or television stations for severe weather warnings and advice. Make sure you have a battery-powered or hand-crank radio on hand; electricity frequently fails during a severe storm.

Severe thunderstorms

A thunderstorm develops in an unstable atmosphere when warm, moist air near the earth's surface rises quickly and cools. The moisture condenses to form rain droplets and dark thunderclouds called cumulonimbus clouds. These storms are often accompanied by high winds, hail, lightning, heavy rain and tornadoes. Thunderstorms are usually over within an hour, although a series of thunderstorms can last for several hours.


The air is charged with electricity during a thunderstorm. The most striking sign of this is lightning. Bolts of lightning hit the ground at about 40,000 kilometres per second — so fast that the lightning appears to be a single main bolt with a few forks, when actually the opposite is true. The main bolt is a whole series of lightning strikes, all taking the same path but at such a pace that the eye cannot distinguish between them.

To estimate how far away the lightning is, count the seconds between the flash of lightning and the thunderclap. Each second is about 300 metres. If you count fewer than 30 seconds, look around for shelter; if fewer than five seconds, take shelter immediately. Lightning is near and you do not want to be the tallest object in the area. It is recommended to wait 30 minutes after the last lightning strike in a severe storm before venturing outside again.

Heavy rain

A heavy rainfall can result in flooding. This is particularly true when the ground is still frozen or already saturated from previous storms. Floods (link to Floods section) may also result if heavy rain coincides with the spring thaw.

Winter storms

On average, the storms and cold of winter kill more than 100 Canadians every year, more than the total number of people killed by hurricanes, tornadoes, floods, lightning and extreme heat combined. The most common types of winter storms cause freezing rain, heavy snow, blowing snow and blizzards.

Blizzards bring snow, bitter cold, high winds and poor visibility in blowing snow. Although snowfall may not be heavy, the poor visibility, low temperatures and high winds are a significant hazard.

Freezing rain occurs when an upper air layer has an above-freezing temperature while the temperature at the surface is below freezing. The snow that falls melts in the warmer layer and as a result, it is rain — not snow — that lands on the surface. But since the temperature is below 0°C, raindrops freeze on contact and turn into a smooth layer of ice spreading on the ground or any other object like trees or power lines. More slippery than snow, freezing rain is tough and clings to everything it touches. A little freezing rain is dangerous; a lot can be catastrophic.


Preparing for a severe storm

If you live in an area where blizzards or heavy snow falls are frequent, consider stocking up on heating fuel and ready-to-eat food, as well as battery-powered flashlights and radios — and extra batteries. See the Build a kit section for more information.

It’s a good idea to get in the habit of trimming dead branches and cutting down dead trees to reduce the danger of these falling onto your house during a storm. You may also want to consider checking the drainage around the house to reduce the possibility of basement flooding after a heavy rain.

When a severe storm is on the horizon, the Meteorological Service of Canada issues watches, warnings and advisories through radio and television stations, the WeatherOffice Website, automated telephone information lines and Environment Canada's Weatheradio.

If a severe storm is forecast, secure everything that might be blown around or torn loose — indoors and outdoors. Flying objects such as garbage cans and lawn furniture can injure people and damage property. If hail is forecast, you may want to protect your vehicle by putting it in the garage. Before a severe thunderstorm, unplug radios and televisions — listen for weather updates on your battery-powered or hand-crank radio.

During a severe storm

If you are indoors, stay away from windows, doors and fireplaces. During thunderstorms, you should also stay away from items that conduct electricity, such as telephones, appliances, sinks, bathtubs, radiators and metal pipes. Do not go out to rescue the laundry on the clothesline because it may conduct electricity.

*You can use a cellphone during a severe storm but it’s not safe to use a land-line telephone.


If you are outdoors when a thunderstorm hits, take shelter immediately, preferably in a building but, failing this, in a depressed area such as a ditch, culvert or cave. Never go under a tree.

If you are caught in the open, do not lie flat but crouch down with your feet close together and your head down (the "leap-frog" position). By minimizing your contact with the ground, you reduce the risk of being electrocuted by a ground charge.

Do not ride bicycles, motorcycles, tractors, golf carts or use metal shovels or golf clubs because they may conduct electricity.

Never go out in a boat during a storm. If you are on the water and you see bad weather approaching, head for shore immediately. Always check the marine forecast before leaving for a day of boating and listen to weather reports during your cruise.

Take cover if hail begins to fall. Do not attempt to cover plants, cars or garden furniture or to rescue animals. Hail comes down at great speed, especially when accompanied by high winds.

When a winter storm hits, stay indoors. If you must go outside, dress for the weather. Outer clothing should be tightly woven and water-repellent. The jacket should have a hood. Wear mittens — they are warmer than gloves — and a hat, as most body heat is lost through the head.

In wide-open areas, visibility can be virtually zero during heavy blowing snow or a blizzard. You can easily lose your way. If a blizzard strikes, do not try to walk to another building unless there is a rope to guide you or something you can follow.

Ice from freezing rain accumulates on branches, power lines and buildings. If you must go outside when a significant amount of ice has accumulated, pay attention to branches or wires that could break due to the weight of the ice and fall on you. Ice sheets could also do the same.

Never touch power lines: a hanging power line could be charged (live) and you would run the risk of electrocution. Remember also that ice, branches or power lines can continue to break and fall for several hours after the end of the precipitation.

In a car

If you are in a car, stop the car away from trees or power lines that might fall on you and stay there.

If you must travel during a winter storm, do so during the day and let someone know your route and arrival time.

When freezing rain is forecast, avoid driving. Even a small amount of freezing rain can make roads extremely slippery. Wait several hours after freezing rain ends so that road maintenance crews have enough time to spread sand or salt on icy roads.

If your car gets stuck in a blizzard or snowstorm, remain calm and stay in your car. Allow fresh air in your car by opening the window slightly on the sheltered side, away from the wind. You can run the car engine about 10 minutes every half-hour if the exhaust system is working well. Beware of exhaust fumes and check the exhaust pipe periodically to make sure it is not blocked with snow. Remember: you can't smell potentially fatal carbon monoxide fumes.

To keep your hands and feet warm, exercise them periodically. In general, it is a good idea to keep moving to avoid falling asleep. If you do try to shovel the snow from around your car, avoid overexerting yourself; shovelling and bitter cold can kill. Keep watch for traffic or searchers.

Emergency kits