Thunderstorms

Thunderstorms develop in warm, humid, and unstable air, most often between May and September. Storms usually only last up to an hour or so, however a line of thunderstorms can last for several hours.

Hail, frequent lightning, damaging winds, heavy winds, and possibly tornadoes are the indicators of severe thunderstorms.

Tornadoes are often difficult to predict, which is why some Severe Thunderstorm Warnings include statements about the potential for tornadoes, even if a Tornado Watch or Warning hasn't been issued.

During very strong thunderstorms with high winds, you should take shelter for safety, just as you should during Tornado Warnings.

Severe Thunderstorms Watches and Warnings

Environment Canada is the federal agency responsible for issuing weather “Watches” and “Warnings“, which are terms that can be confused.

Watches

A severe thunderstorm "Watch" is sent out when weather conditions are right for thunderstorms to develop later in the day. In these circumstances, keep an eye on weather conditions where you are and listen for weather reports on the radio, a weather radio, or a reputable website such or app as Environment Canada.

Warnings

A severe thunderstorm "Warning" is issued for areas in the path of a storm that is causing heavy rain, hail or damaging winds. Severe Thunderstorm Warnings sometimes include the risk of tornadoes, so be prepared to take shelter if threatening conditions exist.

When the sky looks threatening, turn on your radio and monitor weather reports, or go to the Environment Canada app or website for more information. Consider purchasing a weather radio or subscribing to one of the weather alerting services available to the public. If residents in your area are advised to take cover, do so immediately.

Lightning Safety

In Canada, lightning typically kills 10 people and injures 100 each year. Lightning is extremely common and causes more deaths and injuries to Canadians than tornadoes.

During thunderstorms, the air is charged with electricity and this is seen as lightning. Not all lightning reaches the ground, but when it does, electricity can flow to trees, water, rocks, buildings and people.

When there is thunder, there is always lightning (and vice versa). Sometimes, especially at night when lightning flashes are visible for long distances, you can see lightning, but not hear thunder. This is often called “heat lightning“, but it's really just lightning from a storm that is so far away that you can't hear the thunder.

Taking Shelter

If you hear thunder, it means that lightning is close enough to strike you. If you are indoors, stay there, but away from windows, doors, fireplaces, radiators, stoves and appliances. Do not use telephones or computers unless they are wireless. Do not take baths or showers. Metal plumbing, wires and cables can conduct electricity from near-by lightning strikes.

There are no safe spots outdoors during a thunderstorm. Quickly get inside a substantial building or a vehicle with a metal top. If that isn't possible, you need to find the best of the poor options available – try to find a low area such as a ditch, a valley, or a very dense grove of trees, but never take shelter under a solitary tree.

Tents, picnic shelters, gazebos, barns and drive sheds do not provide adequate protection from lightning – get inside a more substantial building or a vehicle. If you are swimming or boating (especially in a boat without lightning protection), get to shore immediately.

If you are in a vehicle, pull away from trees and hydro poles that might fall on you. Do not touch any metal parts inside the vehicle (it's the metal body surrounding you that protects you from lightning, not the rubber tires).

Environment Canada recommends, “If you can hear thunder, seek your best shelter immediately and remain in that shelter for a full 30 minutes after the last thunder to ensure the storm has moved off. Or more simply put, “When the sky roars, get indoors” – and remain there for a full 30 minutes after the last rumble of thunder.”