A Severe Thunderstorm Warning in Canada means a severe thunderstorm is occurring or expected to occur and may produce hazardous conditions such as damaging winds, large hail or heavy rainfall.
Environment and Climate Change Canada issues Severe Thunderstorm Warnings when severe weather is happening or expected to happen. Under Canada’s colour-coded weather alert system, Severe Thunderstorm Warnings can appear as Yellow, Orange or Red alerts depending on the potential risk.
The seriousness of a severe thunderstorm depends on factors such as wind speed, hail size, rainfall, storm duration, location and the expected impacts.
This guide explains what a Severe Thunderstorm Warning means in Canada, why one may be issued, how serious thunderstorms can become, what Yellow, Orange and Red alerts mean and what to do when a Severe Thunderstorm Warning affects your area.
What Is a Severe Thunderstorm Warning?
A Severe Thunderstorm Warning is a weather alert issued when a severe thunderstorm is occurring or expected to occur.
Severe thunderstorms can produce hazardous weather, including damaging winds, large hail and heavy rainfall.
Thunderstorms also produce lightning, which can create a serious hazard even when other severe weather conditions do not develop.
Environment and Climate Change Canada issues warnings when severe weather is happening or expected to happen. Warnings provide information about expected conditions, potential impacts, timing and actions people can take to reduce their risk.
A Severe Thunderstorm Warning is different from a Severe Thunderstorm Watch. A Watch means conditions are favourable for severe thunderstorms to develop, while a Warning means severe weather is happening or expected to happen.
You can learn more about Severe Thunderstorm Warnings and other weather alerts in Canada.
Why Is a Severe Thunderstorm Warning Issued?
A Severe Thunderstorm Warning is issued to alert people when a severe thunderstorm is happening or expected to happen.
The warning gives people time to move to a safe location, monitor changing weather conditions and take precautions against the hazards associated with the storm.
Several weather hazards can contribute to the seriousness of a severe thunderstorm.
Damaging Winds
Severe thunderstorms can produce powerful wind gusts.
Strong winds may damage trees, buildings, power lines and other structures.
Falling trees and branches can block roads, damage vehicles and contribute to power outages.
Large Hail
Some severe thunderstorms produce large hail.
Hail can damage vehicles, roofs, windows, crops and other property.
Large hailstones can also cause injuries to people and animals caught outdoors without adequate shelter.
Heavy Rainfall
Severe thunderstorms can produce intense rainfall over a relatively short period.
Heavy rain may cause water to accumulate quickly on roads and in low-lying areas.
Depending on the intensity and duration of the storm, localized or flash flooding may occur.
Lightning
All thunderstorms produce lightning.
Lightning can cause serious injuries and death, start fires and damage electrical systems.
Environment and Climate Change Canada advises that if you can hear thunder, you are within striking distance of lightning.
The Government of Canada provides additional information about lightning safety and severe thunderstorms, including precautions people can take when thunderstorms approach.
Tornadoes
Some severe thunderstorms can produce tornadoes.
Tornadoes can develop rapidly and create extremely dangerous conditions.
When a tornado is occurring or expected, Environment and Climate Change Canada may issue a separate Tornado Warning for the affected area.
How Serious Is a Severe Thunderstorm Warning?
A Severe Thunderstorm Warning should be taken seriously because severe thunderstorms can produce dangerous and potentially life-threatening weather.
Possible impacts may include:
- Damaging wind gusts
- Large hail
- Heavy rainfall
- Flash flooding
- Frequent lightning
- Falling trees and branches
- Power outages
- Property damage
- Dangerous driving conditions
- Road closures
- Transportation disruptions
- Damage to crops
- Injuries to people and animals
- Tornadoes
The seriousness of a severe thunderstorm depends on the hazards produced by the storm, its duration, location and the vulnerability of the affected area.
Some severe thunderstorms may produce localized impacts, while particularly dangerous storms can cause widespread damage and significant disruptions.
Environment and Climate Change Canada uses Weather Impact Guides to assess how hazardous weather may affect daily life, travel, utilities and services, land and structures, human health and societal recovery.
Severe Thunderstorm Warning Colours in Canada
Severe Thunderstorm Warnings in Canada can appear as Yellow, Orange or Red alerts.
The colours move from Yellow to Orange to Red as the potential risk increases.
The colour assigned to a Severe Thunderstorm Warning is not determined solely by wind speed, hail size or rainfall amounts.
Environment and Climate Change Canada considers both the expected impacts of the weather event and confidence in the forecast when selecting an alert colour.
Yellow Warning – Severe Thunderstorm
A Yellow Warning – Severe Thunderstorm indicates hazardous weather that may cause damage, disruption or health impacts.
Environment and Climate Change Canada describes the expected impacts of Yellow alerts as generally moderate, localized and/or short-term.
During a Yellow Warning – Severe Thunderstorm, possible impacts may include strong winds, hail, heavy rainfall, localized flooding, power outages and property damage.
Thunderstorms can develop and change quickly, so conditions may deteriorate over a relatively short period.
Although Yellow represents the lowest of Canada’s three alert colours, severe thunderstorms can still create dangerous conditions.
People in affected areas should monitor current weather information and move to a safe location when severe weather approaches.
Orange Warning – Severe Thunderstorm
An Orange Warning – Severe Thunderstorm indicates a greater level of potential risk than a Yellow alert.
Orange alerts indicate severe weather that is likely to cause significant damage, disruption or health impacts.
The expected impacts may be major, widespread and/or last for several days.
During an Orange Warning – Severe Thunderstorm, possible impacts may include significant wind damage, large hail, flooding, widespread power outages and major transportation disruptions.
Severe weather may damage buildings, trees, power lines and other infrastructure.
People in affected areas should closely monitor official information, move to a safe location and follow instructions from local authorities and emergency officials.
Red Warning – Severe Thunderstorm
A Red Warning – Severe Thunderstorm represents the highest level of potential risk within Canada’s colour-coded weather alert system.
Red alerts indicate very dangerous and possibly life-threatening weather that is expected to cause extreme damage and disruption.
The expected impacts may be extensive, widespread and prolonged.
During a Red Warning – Severe Thunderstorm, exceptionally dangerous conditions may cause extensive property and infrastructure damage, widespread power outages, major transportation disruptions and serious risks to life and safety.
Red alerts are rare and communicate the most serious potential weather risk within Canada’s alert system.
People in affected areas should immediately follow the safety information included in the warning and instructions from local authorities and emergency officials.
Environment and Climate Change Canada provides additional information about Yellow, Orange and Red weather alerts and how the colours communicate increasing levels of potential risk.
Yellow vs Orange vs Red Severe Thunderstorm Warnings
The main difference between Yellow, Orange and Red Severe Thunderstorm Warnings is the level of potential risk communicated by the alert colour.
A Yellow warning indicates hazardous weather that may cause moderate, localized or short-term impacts.
An Orange warning indicates severe weather that is likely to cause significant impacts that may be major, widespread or last for several days.
A Red warning indicates very dangerous and potentially life-threatening weather that is expected to cause extreme impacts that may be extensive, widespread and prolonged.
The warning colour is selected using both expected impacts and forecast confidence.
Environment and Climate Change Canada’s Alert Colour Matrix explains how forecasters combine expected impacts and forecast confidence when selecting Yellow, Orange or Red.
Can the Colour of a Severe Thunderstorm Warning Change?
The colour assigned to a Severe Thunderstorm Warning reflects the potential risk associated with the expected weather event.
Environment and Climate Change Canada considers expected weather impacts and forecast confidence when selecting alert colours.
Thunderstorm conditions, expected impacts and forecast confidence may change as a storm develops and new information becomes available.
For this reason, people should continue monitoring the latest Severe Thunderstorm Warning rather than relying only on an earlier alert.
Always read the complete warning because it may include additional information about expected hazards, timing, affected locations, potential impacts and recommended actions.
Severe Thunderstorm Warning vs Severe Thunderstorm Watch
A Severe Thunderstorm Warning and Severe Thunderstorm Watch communicate different levels of certainty about severe weather.
A Severe Thunderstorm Watch means conditions are favourable for severe thunderstorms to develop.
A Severe Thunderstorm Warning means severe weather is happening or expected to happen.
A Watch gives people advance notice that they should monitor changing conditions and be prepared to take action.
A Warning indicates a more immediate threat and means people in the affected area should take appropriate precautions.
A Severe Thunderstorm Watch may be upgraded to a Warning when confidence increases that severe weather will occur.
Severe Thunderstorm Warning vs Tornado Warning
A Severe Thunderstorm Warning and Tornado Warning are both urgent weather alerts, but they communicate different hazards.
A Severe Thunderstorm Warning indicates that a severe thunderstorm is happening or expected and may produce hazards such as damaging winds, large hail and heavy rainfall.
A Tornado Warning indicates that a tornado is occurring or expected to occur.
Some severe thunderstorms can produce tornadoes.
When a tornado threat develops, Environment and Climate Change Canada may issue a Tornado Warning for the affected area.
Severe Thunderstorm Warning vs Rainfall Warning
A Severe Thunderstorm Warning may include heavy rainfall as one of several hazards associated with a thunderstorm.
A Rainfall Warning specifically focuses on heavy or prolonged rainfall and the impacts it may produce.
Severe thunderstorms can produce intense rain over a short period, while a Rainfall Warning may be issued for rainfall events that last for many hours or longer.
Both alerts may sometimes be issued when severe thunderstorms and significant rainfall are expected to affect the same area.
What Can Happen During a Severe Thunderstorm Warning?
The impacts of a Severe Thunderstorm Warning depend on the severity, duration and location of the storm.
Damaging Wind Gusts
Strong thunderstorm winds can damage trees, power lines, buildings and other structures.
Loose objects may also be blown through the air and create additional hazards.
Large Hail
Large hail can damage roofs, windows, vehicles, crops and other property.
People and animals caught outdoors may also be injured.
Heavy Rain and Flooding
Intense rainfall may overwhelm drainage systems and cause water to accumulate quickly.
Roads, underpasses, basements and other low-lying areas may flood.
Frequent Lightning
Lightning can cause injuries, deaths, fires and damage to electrical systems.
People should move to a safe location when thunder is heard.
Power Outages
Damaging winds, lightning and falling trees may affect electrical infrastructure.
Power outages may continue after the storm ends while damage is repaired.
Property Damage
Severe thunderstorms can damage homes, vehicles, businesses and infrastructure.
The extent of the damage depends on the hazards produced by the storm and the vulnerability of the affected area.
Transportation Disruptions
Heavy rain, flooding, fallen trees and damaged infrastructure may affect roads and transportation services.
Disruptions can continue after the storm has moved away.
What Should You Do During a Severe Thunderstorm Warning?
The appropriate response to a Severe Thunderstorm Warning depends on the alert colour, location, expected hazards and information included in the warning.
Move Indoors
Move to a sturdy building when severe weather approaches.
Avoid remaining outdoors, in open areas or near tall isolated objects during a thunderstorm.
Stay Away From Windows
Strong winds and hail may break windows.
Move away from windows, skylights and glass doors when dangerous conditions are expected.
Monitor Current Conditions
Check current weather alerts, radar and forecasts.
Severe thunderstorms can develop and change rapidly.
Environment and Climate Change Canada provides official weather radar and satellite services that can help people monitor approaching storms.
Avoid Water
Lightning can create serious hazards near lakes, rivers, pools and other bodies of water.
Leave the water and move to a safe location when thunderstorms approach.
Avoid Flooded Roads
Heavy rainfall may cause roads to flood.
Never attempt to drive through floodwater because the depth, current and condition of the road may be difficult to determine.
Follow Official Information
Continue monitoring weather information and follow instructions from Environment and Climate Change Canada and local authorities.
Can You Drive During a Severe Thunderstorm Warning?
Driving during a Severe Thunderstorm Warning may be dangerous depending on the hazards produced by the storm.
Heavy rainfall can reduce visibility and cause water to accumulate on roads.
Strong winds may make vehicles more difficult to control, while hail can reduce visibility and damage vehicles.
Fallen trees, power lines and flooding may block roads.
If severe weather is approaching, consider delaying unnecessary travel and move to a safe location when possible.
Never drive through flooded roads or around road closures and barriers.
How Long Does a Severe Thunderstorm Warning Last?
There is no standard duration for a Severe Thunderstorm Warning.
The length of the warning depends on the development, movement and duration of the storm.
Some severe thunderstorms may move through an area relatively quickly, while larger storm systems may produce hazardous conditions for longer periods.
Conditions can also change rapidly.
Continue monitoring current weather information until the warning ends and the storm has moved away from your area.
How Can You Check Current Severe Thunderstorm Warnings?
Current Severe Thunderstorm Warnings and other weather alerts can be checked through Environment and Climate Change Canada’s official weather services.
The Weather Information map allows users to view current Yellow, Orange and Red alert areas and read complete alert information.
You can use Environment and Climate Change Canada’s official Weather Information map to check current forecasts and alerts across Canada.
The WeatherCAN application also provides official forecasts, weather alerts and customizable notifications.
Frequently Asked Questions About Severe Thunderstorm Warnings
A Severe Thunderstorm Warning means a severe thunderstorm is happening or expected to happen and may produce hazardous weather such as damaging winds, large hail or heavy rainfall.
A Severe Thunderstorm Warning should be taken seriously. Severe thunderstorms can produce damaging winds, large hail, flooding, frequent lightning, power outages and potentially life-threatening conditions.
A Yellow Warning – Severe Thunderstorm indicates hazardous weather that may cause moderate, localized or short-term impacts.
An Orange Warning – Severe Thunderstorm indicates severe weather that is likely to cause significant impacts that may be major, widespread or last for several days.
A Red Warning – Severe Thunderstorm represents the highest alert colour and indicates very dangerous and potentially life-threatening weather that is expected to cause extreme impacts.
A Severe Thunderstorm Watch means conditions are favourable for severe thunderstorms to develop. A Severe Thunderstorm Warning means severe weather is happening or expected to happen.
A severe thunderstorm can produce a tornado. If a tornado threat develops, Environment and Climate Change Canada may issue a Tornado Warning for the affected area.
People should move to a safe location when severe weather approaches. Thunderstorms can produce lightning, damaging winds, hail and heavy rainfall.
Sources
- https://www.canada.ca/en/services/environment/weather/severeweather/weather-alerts.html
- https://www.canada.ca/en/environment-climate-change/services/lightning/safety.html
- https://www.canada.ca/en/services/environment/weather/severeweather/weather-alerts/weather-impact-guides.html
- https://www.canada.ca/en/services/environment/weather/severeweather/weather-alerts/colour-coded-alerts.html
- https://www.canada.ca/en/services/environment/weather/severeweather/weather-alerts/choose-alert-colours.html
- https://www.canada.ca/en/services/environment/weather/radar-satellites.html
- https://www.canada.ca/en/environment-climate-change/services/weather-general-tools-resources/weather-webmapping.html
- https://www.canada.ca/en/environment-climate-change/services/weather-general-tools-resources/weathercan.html