Severe thunderstorms

A thunderstorm is an atmospheric disturbance that involves lightning and thunder. It may be accompanied by torrential rain, hail or high winds.

A severe thunderstorm can cause flooding, fires, power failures and electrocution, and result in serious damage.

You can limit the dangers during a severe thunderstorm:

Be prepared

Find out about weather alerts in effect in your region or the area where you are going. Take those alerts into account when planning your activities and travel.

Take shelter as soon as you hear thunder

Sheltering as soon as thunder roars remains the safest behavior.

To find out the distance separating you from the thunderstorm, count the seconds between the flash of lightning and the thunderclap. One second represents approximately 300 metres. For example, if five seconds elapse between the lightning and the thunder, the thunderstorm is about 1500 m (1.5 km) from where you are. You must take shelter if the thunderstorm is less than 10 km away.

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Follow safety rules

Follow the safety rules wherever you may be. In the case of severe thunderstorms forecast, follow the instructions provided by the authorities.


To stay safe when indoors, do as follows:

  • Disconnect electrical devices.
  • Close doors and windows securely.
  • Find shelter in a room at the centre of the building, as lightning can go through outside walls, windows and doors.
  • Stay away from objects that conduct electricity, such as household appliances, sinks, bathtubs, radiators and metal pipes.
  • Do not use televisions or computers because they can be seriously damaged by lighting surges.
  • Use battery-operated devices instead.
  • Avoid using phones connected to landlines because lightning travels along electrical wiring and cords. Use wireless or cell phones instead.
  • Wait about 30 minutes after the last rumble of thunder before going outside.

In a vehicle

A vehicle with a hard-topped roof (not a convertible) can serve as shelter and protect you from lightning. It is preferable not to drive during the thunderstorm and to stay far away from power lines. If a power line falls on your vehicle, remain inside the vehicle and wait for help.


If you are outdoors during a thunderstorm, the following advice will enable you to reduce the risks related to lightning:

  • Seek shelter in the lowest area that you can find, for example a ditch.
  • Squat down.
  • Put your head against your knees and cover it with your arms.
  • If possible, put insulating material such as a plastic bag between the ground and yourself.
  • Be ready to move in the event of flash flooding.

Stay away from:

  • Trees
  • Telephone poles
  • Power lines
  • Objects that conduct electricity, such as motorcycles, lawnmowers, golf clubs or umbrellas
  • Water
  • Hills or any elevated places in a open area

If you are in the woods, seek shelter under a thick growth of small trees or bushes.

If you are in a boat, head for shore immediately.

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Do not rely on inadequate shelter

Avoid barns with a sheet-metal roof that is supported by wooden beams. In addition, avoid open constructions, such as bus shelters.

Act immediately if a person is struck by lightning

If a person near you is struck by lightning, it is a medical emergency. Call 911 or go to the closest hospital centre. Be aware that:

  • You can touch or transport the person to a safe location without any danger, as he or she does not carry an electrical charge.
  • You can administer artificial respiration or CPR until help arrives.
  • Anyone who is struck by lightning must consult a physician, even if there is no apparent injury and the person feels well.

Make your environment safe and take note of the damage

If your home was damaged, you must inform:

  • Your fire department to verify that you can enter your home
  • Your insurer
  • The financial institution that gave you a mortgage

Below is advice to follow when you return to your home once you have obtained confirmation that it is safe:

  • Restore electricity, heating and water, unless the equipment is damaged.
  • Dry out the premises and clean the home.
  • Determine which personal items must be cleaned by experts.
  • Make sure that water, food and medications are fit for consumption.

Other recommendations apply if your home was damaged by a flood.

Know what to do after a disaster

Consult the After a disaster section to learn instructions and recommendations for getting back to normal in a safe manner.

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