Spring and Summer Hazards
As a normal feature of the Canadian summer, severe weather can manifest itself as thunderstorms, tornadoes or excessive heat. In recent years, impacts from severe weather events have become costly as the numbers of floods and forest fires increase. But not all hazards in the summer months are a result of severe weather. Other hazards, from excessive heat to frost, can also have serious impacts on Canadians and their property.
Follow these links to find out more about Canada’s summer weather hazards:
You may also wish to visit Environment Canada’s archive of climate and historical weather on significant events and trends in summer severe weather.
Fog
Fog occurs when tiny water droplets suspended in the air reduce visibility to less than one kilometre. It is different from cloud only because fog touches the earth’s surface.
Driving any vehicle in low visibilities due to fog can be hazardous, therefore speeds should be reduced accordingly.
Frost
Frost is atmospheric moisture that crystallizes directly on the ground and on exposed objects, such as rooftops, when temperatures are below freezing. Frost forms under conditions that would normally create dew if the temperature were above freezing at the point of formation. Although it looks very pretty, frost can cause serious harm to flowers and plants if it occurs during the growing season. As such, care should be taken to protect frost-sensitive plants when such conditions are forecast.
Hail
Hail is formed when updrafts in thunderclouds carry raindrops upward into extremely cold areas of the atmosphere, where they freeze and merge into lumps of ice. When the lumps become too heavy to be supported by the updraft, they fall to the ground at speeds of up to 100 km/h or more.
Hailstones as large as grapefruit have been reported in Canada, but even smaller hail can be dangerous and can cause extensive damage in a matter of minutes. If a hailstorm is approaching, take steps to protect yourself and your property.
Heat and Humidity
Humidity is the amount of water vapour in the air. In forecasting, relative humidity describes the percentage of moisture in the air in comparison to how much there is when the air is saturated. The higher the reading, the greater the likelihood of precipitation, dew and fog. Relative humidity is normally highest at dawn, when the temperature is at its lowest point of the day.
High humidity makes people feel hotter than they would on a drier day. That’s because the perspiration that occurs to cool us down cannot evaporate as readily in moist, saturated air. To better describe how hot it feels in such circumstances, Canadian meteorologists developed the humidex, a parameter that combines temperature and humidity in order to reflect the perceived temperature.
When the humidex is high, people can experience serious health problems such as cramps, exhaustion and heat stroke. It is important that you are sure to take the appropriate steps to protect yourself during hot, humid weather.
Lightning
Lightning is an electrical discharge caused by a build up of static electricity between thunderclouds, or between thunderclouds and the ground. It can deliver as much as 100 million volts of electricity and strike a target up to 16 kilometres away, making it an extremely dangerous form of severe weather.
Thunder is the noise created when air suddenly expands from the heat of a lightning discharge. If you count the seconds between a flash of lightning and a thunder clap, you can tell approximately how close the lightning is to you: each second representing about 300 metres. Remember though, if you can hear thunder you are within striking distance, so head indoors or take other steps if you are caught out in the open.
For more interesting facts and tips about lightning, visit our Resource Centre.
Storm Surges
A storm surge is an abnormal rise in water level, that occurs when a high and forceful dome of wind-driven ocean water sweeps along the coastline near where the eye of a tropical or non-tropical storm makes landfall, or passes close to the coast.
Often accompanied by high waves, storm surges can cross the normal high-water mark defined by the tide, and cause damage to infrastructure along coastal areas. They can also cause coastal flooding as far inland as several kilometres. Make sure to take appropriate steps to protect yourself and your property if a storm surge warning is issued.
Thunderstorms
As its name implies, a thunderstorm is a localized storm that produces lightning and thunder. Caused by strong, rising air currents, thunderstorms are most likely to develop when the weather is hazy, hot and humid.
Thunderstorms are a common occurrence in many parts of Canada during the summer months. Often characterized by heavy rain and strong winds, they are sometimes accompanied by hail and tornadoes.
When a severe thunderstorm warning is in effect, know where you can take shelter when the threat becomes imminent.
Tornadoes
There are an average of 80 tornadoes reported in Canada each year, most between the months of May and September. Certain areas of the country are more prone to these violent storms, including southern Ontario, southwestern Quebec, Alberta, and a band stretching from southern Saskatchewan and Manitoba through to Thunder Bay. The interior of British Columbia and western New Brunswick are also tornado zones.
Warm, humid weather and the thunderstorms that develop when cool northern air masses collide with very warm, or even hot air set the stage for the formation of a tornado. What sets it in motion are updrafts and downdrafts in the atmosphere that cause the base of the thunder cloud to rotate.
Tornadoes often appear behind a shroud of heavy rain or hail in a sky that is green, yellow or black. They descend as roaring funnel clouds that can move at speeds of up to 90 km/h. Very large thunderstorms can spawn multiple tornadoes or a single tornado with a number of smaller but intense vortices within it.
Tornadoes typically snake erratically from southwest to northeast. They can last for a few minutes or a few hours, and usually leave a path of destruction in their wake. The strongest tornadoes, which rank as an F5 on the Fujita scale, boast winds of just over 500 km/h.
If a tornado is approaching your area, seek shelter immediately.
Wind
A strong wind does not only occur on a large scale from tropical storms or low pressure systems and fronts, but also on a small scale, from thunderstorms, Chinooks or the local geography.
Strong winds, and especially gusty winds, can cause property damage or turn any loose item into a dangerous projectile, and create unsafe travelling conditions that affect your ability to safely steer your car.
When there is a wind warning for your area, you should expect inland winds to be blowing steadily at 60-65 km/h or more, or winds that are gusting up to 90 km/h or more. Secure or put away loose objects such as outdoor furniture or garbage cans, put your car in the garage, and bring livestock to shelter.
Safety Tips: High wind in combination with heavy rain can increase the risk of tree limb breakage or trees uprooting. After heavy winds, check your property for dead branches and damage. With winds between 60 and 70 km/h, you will have difficulty with balance and walking against the wind. Twigs and small branches could also blow off trees and cause a hazard, so stay inside until it is safe.
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