Weather Impact Guides

We use our Impact Guides to help us decide the colour of our weather alerts.

These guides replace the former criteria for public weather alerts. They give you details to help you know what to expect from the weather.

Remember: All weather can have serious results. It can be life-threatening at any impact level. Important safety information when using our Impact Guides.

Example Impact Guide

Every impact level for each of the weather hazards has a similar structure. The example Impact Guide will show you what you can expect in each guide.

For each weather hazard, you will see three levels of impact (moderate, high, or extreme).

At each level of impact, we describe how the weather will affect general daily life, travel, utilities and services, land and structures, human health, and societal recovery.

You will see how the severity of the impacts increase, progressing from moderate to high to extreme.

Moderate

• General: limited disruption to daily life
• Travel: travel delays possible
• Utilities and services: disruption to utilities and services may occur
• Land and structures: minor damage to property
• Human health: increased risk of injury, illness, or death
• Societal recovery: relatively quick recovery

High

• General: considerable disruption to daily life
• Travel: major travel disruption
• Utilities and services: utilities and services likely impacted
• Land and structures: substantial property damage
• Human health: higher risk of injury, illness, or death
• Societal recovery: a few days for recovery

Extreme

• General: lengthy disruption to many aspects of daily life
• Travel: prolonged travel disruption
• Utilities and services: significant impact to utilities and services
• Land and structures: extensive property damage
• Human health: highest risk of injury, illness, or death
• Societal recovery: long duration recovery

Coastal flooding/storm surge

Adverse impacts are expected due to elevated water levels in coastal regions.

Moderate

• Travel routes difficult or dangerous to navigate
• Local utility outages
• Some overland and basement flooding
• Coastal shoreline erosion in sensitive areas
• Water over banks and in yards or campgrounds
• Properties in coastal locations affected by spray, wave overtopping or sewage backup
• Damage to shoreline adjacent buildings/structures/boats
• People close to the shore are at risk of injury due to strong currents or the rapid approach of unexpectedly larger waves

High

• Widespread travel disruptions
• Dangerous route conditions
• Widespread utility outages
• Coastal water well contamination from sea water
• Main floor flooding affecting properties and parts of communities
• Erosion and/or damage to shoreline and riverbanks
• Infrastructure including docks, breakwaters, retaining walls, dikes damaged or destroyed
• Major damage to buildings and structures
• Essential services delays; significant delays for emergency responders
• Increased risk of injury/fatalities from landslide or drowning

Extreme

• Travel routes very dangerous and/or impassable, including nearshore roads and evacuation routes
• Widespread flooding
• Prolonged, widespread utility outages
• Vehicles destroyed or washed away
• Widespread building and structural damage or destruction
• High risk of injury/fatalities from landslide or drowning
• Critical infrastructure including dams, dikes and pumping infrastructure compromised/destroyed
• Essential service disruption

Cold (including Arctic outflow)

Adverse impacts are expected due to extreme cold temperatures or wind chill.

Moderate

• Risk of cold injury, such as frostnip, frostbite or hypothermia, without adequate protection
• Higher risk of illness or death from being exposed to cold
• Road de-icing may be less effective
• Vehicle charging, battery levels, tire performance may be affected
• Water pipes freeze or burst
• Minor tree and vegetation damage
• Outdoor work adjusted
• Outdoor events postponed or cancelled

High

• Very high risk of cold injury, such as frostbite and hypothermia, without adequate protection
• Road de-icing less effective
• Vehicle charging, battery levels, tire performance affected
• Impacts to critical infrastructure, such as water mains
• Tree and vegetation damage
• Outdoor work suspended

Extreme

• Severe risk of cold injury, such as frostbite or hypothermia, without adequate protection
• Travel or outdoor activities not safe
• Widespread tree and vegetation damage
• Risk of widespread impacts to utilities and critical infrastructure

Frost

Adverse impacts are expected from cold temperatures that have the potential to damage plants.

Moderate

• Widespread damage to plants or crops

Heat

Adverse impacts are expected due to significant heat and/or Humidex values.

Note: Extreme heat can create favorable conditions for wildfires and poor air quality.

Moderate

• Increased risk of illness or death
• Brownouts and/or power outages
• Animals at risk
• Outdoor events delayed and/or adjusted
• Workforce impacts due to higher temperatures indoors and outdoors

High

• Higher risk of illness or death
• Localized travel disruption
• Risk of localized water shortages
• Brownouts and power outages
• Animals at higher risk
• Crops, plants, and gardens at risk of damage
• Items, vehicles or materials left in direct sunlight at risk of damage
• Some damage to critical infrastructure
• Outdoor events delayed and/or cancelled
• High impacts on essential services

Extreme

• Extreme risk of illness or death
• Widespread travel disruption due to route damage and/or aircraft, train, or vehicle performance
• Excess demand and potential damage to utilities, including energy and water
• Power outages and water shortages
• Animals at extreme risk
• Crops, plants, and gardens at risk of extreme damage
• Items, like vehicles or materials left in direct sunlight at risk of damage or destruction
• Damage to critical infrastructure
• Outdoor events delayed and/or cancelled for multiple days
• Prolonged, widespread impacts on essential services

Hurricanes and tropical storms

Adverse impacts are expected from:

• a hurricane (producing coastal winds of ≥ 118 km/h)
• a tropical storm (producing winds of 63–117 km/h)
• coastal flooding (storm surge)
• high waves with an implied threat of local flooding from heavy rains

Visit the Canadian Hurricane Centre for forecasts, warnings, and watches.

Moderate

• Travel delays due to road closures, flooding, debris, power outages
• Utility outages
• Some damage to buildings and structures including siding and roofing

High

• Widespread travel disruption
• Flash flooding
• Widespread utility outages
• Major damage to buildings and structures
• Risk of injury from blown debris and storm cleanup-related accidents
• Some critical infrastructure damage
• Essential services delays; significant delays for emergency responders

Extreme

• Widespread, prolonged travel disruption
• Widespread, prolonged utility outages
• Widespread building and structural damage or destruction
• Risk of life-threatening injury
• Critical infrastructure compromised/destroyed
• Prolonged, widespread essential services disruption

Ice (freezing rain, freezing drizzle, flash freeze)

Adverse impacts are expected due to icy surfaces and ice buildup.

Moderate

• Travel delays due to icy routes and vehicle collisions
• Ice accumulation on powerlines, bridges and other infrastructure
• Some utility outages
• Some property damage, broken branches
• Risk of injury due to slips and falls or falling ice or debris

High

• Significant travel delays, multiple vehicle collisions
• Damage to powerlines, bridges, and other infrastructure
• Widespread utility outages
• Major property damage, treefall
• Increased risk of injury due to slips and falls or falling ice or debris

Extreme

• Widespread, dangerous travel conditions, including vehicle pileups
• Utility poles and towers collapse
• Long duration, widespread utility outages
• Widespread property damage, trees destroyed
• Critical infrastructure compromised

Rain

Adverse impacts are expected due to significant rainfall amounts.

Moderate

• Travel delays due to overland flooding, water pooling on routes, traffic rerouting
• Some utility outages
• Basement flooding
• Outdoor events postponed or cancelled

High

• Widespread overland flooding, roads covered by water
• Some washouts, landslides; some communities inaccessible
• Widespread travel delays
• Utility outages likely, power loss can lead to pump failures
• Widespread residential and business flooding
• Injuries or fatalities from drowning, landslides
• Vehicles damaged
• Outdoor events cancelled

Extreme

• Major roads/highways/bridges washed out or blocked by landslides
• Travel unsafe
• Widespread outages
• Dams, levies and dikes, and/or pumps, compromised
• Major destruction and inundation of buildings
• Sewer backups and wastewater contamination
• Shoreline and riverbank erosion and damage
• Agriculture and livestock loss
• Vehicles damaged and/or washed away
• Multiple injuries and/or fatalities from drowning, landslides

Snow

Adverse impacts are expected due to significant snowfall accumulations.

Moderate

• Travel disruptions due to route closures, vehicle collisions, and conditions
• Injuries due to exertion, falls

High

• Travel dangerous due to accumulated snow, route closures, and multiple vehicle collisions
• Long travel delays
• Property and/or tree damage
• Roofs at increased risk of collapsing under the weight of snow

Extreme

• Travel extremely unsafe or impossible
• Significant property and/or tree damage
• Damage to some critical infrastructure
• Snowed-in residents, numerous injuries due to exertion and/or collapsing structures/trees
• Essential services delays; significant delays for emergency responders

Snow squall

Adverse impacts are expected due to localized, intense bands of snow, generated by open water or a front.

Moderate

• Travel disruptions due to route closures, vehicle collisions, and conditions
• Injuries due to exertion, falls

High

• Travel dangerous due to accumulated snow, route closures, and multiple vehicle collisions
• Long travel delays expected
• Stranded vehicles and passengers
• Property and/or tree damage
• Some utility outages
• Roofs at increased risk of collapsing under the weight of snow
• Significant delays for emergency responders

Extreme

• Very dangerous and/or impassable routes
• Prolonged, widespread travel delays
• Vehicles and passengers stranded for long periods
• Utility outages
• Significant impact on delivery of essential goods and services

Thunderstorms

Adverse impacts are expected due to hail and/or wind and/or rain associated with thunderstorms.

Note: Lightning can occur with any thunderstorm. Learn more about lightning safety.

Moderate

• Some travel delays
• Driving conditions difficult
• Local utility outages
• Damage to roofs, fences, soft shelters and trees
• Potential for flooding
• Risk of injury

High

• Travel delays and/or cancellations
• Utility outages
• Significant damage to buildings, structures and trees
• Potential for dangerous flooding; fast moving water can sweep vehicles away and damage infrastructure
• Risk of serious injury
• Some critical infrastructure damage
• Essential services disruption

Extreme

• Prolonged or widespread travel delays or cancellations
• Prolonged or widespread utility outages
• Buildings and many trees destroyed
• Potential for extreme flooding; fast moving water will sweep vehicles away and damage infrastructure
• Risk of life-threatening injury
• Critical infrastructure compromised/destroyed
• Prolonged essential services disruption

Tornadoes

Adverse impacts are expected from violently rotating, damaging winds associated with thunderstorms.

Moderate

• Travel routes difficult or dangerous to navigate
• Travel delays due to road closures, debris, power outages
• High-sided vehicles pushed around
• Local utility interruptions or outages
• Outdoor events postponed or cancelled
• Damage to trees
• Minor damage to property including buildings, vehicles, signs, fences, loose items
• Risk of injury from flying or falling debris

High

• Travel routes dangerous to navigate
• Widespread travel disruption
• Widespread utility outages
• Significant, widespread tree damage
• Essential services delays; significant delays for emergency responders
• Significant damage to buildings and property including boats, sheds, RVs, small planes
• Increased risk of serious injury from flying or falling debris or collapsing structures/trees
• Some critical infrastructure damage

Extreme

• Very dangerous and/or impassable travel routes
• Prolonged, widespread travel disruption including vehicles blown around or destroyed
• Prolonged, widespread utility outages
• Transmission/utility tower collapse
• Stands of trees (forests, orchards, parks) flattened/destroyed
• Prolonged essential services disruption
• Homes/buildings destroyed
• High risk of serious injury from flying/falling debris or collapsing structures/trees
• Major agriculture/livestock losses
• Critical infrastructure compromised/destroyed; supply chain impacted

Visibility (including blizzards, blowing snow, dust, fog)

Adverse impacts are expected due to widespread poor visibility.

Moderate

• Routes difficult to navigate
• Travel delays and disruptions due to route closures, collisions, gridlock

High

• Travel dangerous to impossible
• Widespread travel disruption, multiple collisions
• Increased risk of disorientation or becoming lost over short distances
• Some vehicles and passengers stranded
• Major delays for emergency response

Extreme

• Travel extremely dangerous and/or impossible
• Prolonged, widespread travel disruption
• Vehicles and passengers stranded for long periods
• Significant impact on delivery of essential goods and services
• High risk for mass casualty incidents affecting emergency responders and hospitals

Wind

Adverse impacts are expected from damaging winds.

Moderate

• Minor travel delays due to debris and outages
• Some short term utility outages
• Larger tree branches broken; some yard items blown about
• Risk of injury from flying or falling debris
• Outdoor events postponed or cancelled

High

• Major travel delays due to debris and outages
• High-sided vehicles pushed around
• Widespread utility outages
• Some roof damage
• Small to medium trees snapped
• Some damage to critical infrastructure
• Increased risk of injury from flying or falling debris
• Outdoor events cancelled
• Essential services disruption

Extreme

• Widespread, prolonged travel delays due to road closures, debris, downed power lines
• High-sided vehicles tipped or flipped
• Long duration, widespread utility outages
• Structural damage to homes and buildings
• Significant damage to trees including orchards, parks
• Critical infrastructure compromised
• High likelihood of injury due to flying or falling debris
• Prolonged essential services disruption

Winter storm

Adverse impacts are expected from multiple types of severe winter weather.

Moderate

• Travel disruptions due to route closures, vehicle collisions, and winter conditions
• Local utility interruptions or outages
• Larger tree branches broken

High

• Dangerous travel conditions; widespread travel delays and road closures
• Vehicles and passengers stranded, numerous vehicle collisions
• Utility outages
• Structural damage to roofs/buildings
• Significant tree damage
• Essential services delays; significant delays for emergency responders

Extreme

• Travel unsafe; prolonged, widespread travel delays
• Vehicles and passengers stranded for long periods
• Prolonged, widespread utility outages
• Major damage and destruction to homes and buildings
• Stands of trees flattened or destroyed
• Prolonged essential services disruption

Glossary

Useful terms to understand the impact guides:

Critical infrastructure

• Physical systems and facilities—like power grids, water treatment plants, hospitals, and transportation networks—that support the functioning of society

Essential services

• Activities or functions provided by people or organizations—like health care, emergency response, and public transit—that rely on critical infrastructure to operate

Prolonged

• Impacts will continue for a long time or longer than usual

Utilities

• Services that include electricity, internet, cellular and landline telephone, water, and gas supply

Widespread

• Impacts will be found or distributed across a wide area