A Frost Advisory in Canada is issued when temperatures are expected to fall near or below freezing during the growing season, creating conditions that may damage or kill frost-sensitive plants and crops.
Frost can develop when surfaces cool enough for water vapour to form ice crystals. Plants, gardens and agricultural crops may be damaged when exposed to sufficiently cold temperatures.
Environment and Climate Change Canada issues Frost Advisories to alert gardeners, farmers and other people when frost may affect vulnerable plants and crops.
The seriousness of a frost event depends on several factors, including temperature, duration, local geography and the type of vegetation exposed to the cold.
This guide explains what a Frost Advisory means in Canada, why one is issued, how serious frost can be, potential impacts and what to do when an advisory affects your area.
What Is a Frost Advisory?
A Frost Advisory is a weather alert issued when frost is expected during the growing season and may damage or kill frost-sensitive plants and crops.
Frost develops when surfaces become cold enough for water vapour to form ice crystals.
Plants can be particularly vulnerable to frost because cold temperatures may damage plant tissues.
The severity of the damage depends on the temperature, length of exposure and sensitivity of the plant.
Frost Advisories are particularly important during the spring and fall when temperatures can fall significantly overnight while plants are actively growing.
Environment and Climate Change Canada includes Frost Advisories among the official types of weather alerts in Canada.
Why Is a Frost Advisory Issued?
A Frost Advisory is issued to alert people when frost is expected to create a risk to frost-sensitive plants and crops.
The advisory gives gardeners, farmers and other people time to protect vulnerable vegetation before temperatures fall.
Several factors contribute to the potential impacts of a frost event.
Cold Temperatures
Cold temperatures are the primary factor associated with frost development.
When temperatures near the ground fall sufficiently, frost may develop on plants and other surfaces.
Clear Skies
Clear skies can allow heat stored near the ground to escape more quickly overnight.
This process can cause surface temperatures to decrease and contribute to frost development.
Light Winds
Light winds can create favourable conditions for frost formation.
When winds are calm or light, colder air can remain near the ground.
Local Geography
Valleys and other low-lying areas may be particularly vulnerable to frost.
Cold air can move downhill and collect in lower elevations, creating colder conditions than nearby areas.
The Growing Season
Frost Advisories are particularly relevant during the growing season.
Plants and crops may be actively growing and vulnerable to damage when unexpected cold temperatures occur.
Environment and Climate Change Canada provides additional information about weather alerts in Canada and the advisories used to communicate potentially hazardous weather conditions.
How Serious Is a Frost Advisory?
A Frost Advisory should be taken seriously by gardeners, farmers and anyone responsible for frost-sensitive plants.
Possible impacts may include:
- Damage to garden plants
- Damage to agricultural crops
- Death of frost-sensitive vegetation
- Reduced crop yields
- Damage to flowers and buds
- Damage to young plants
- Delayed plant growth
- Financial losses for agricultural producers
- Damage to fruit trees and vineyards
- Disruptions to planting and harvesting activities
The seriousness of a frost event depends on temperature, duration, plant sensitivity, growing stage and local conditions.
Some plants may tolerate brief exposure to cold temperatures.
Others may be damaged or killed by a relatively short frost event.
Local conditions can also vary significantly.
A low-lying area may experience frost while nearby locations remain above freezing.
What Causes Frost?
Frost can form when surfaces cool to temperatures that allow water vapour to become ice crystals.
Several weather and environmental conditions can influence frost development.
Falling Temperatures
Frost becomes more likely when temperatures near the ground approach or fall below freezing.
Surface temperatures may sometimes be colder than the official air temperature measured at a weather station.
Radiational Cooling
After sunset, the ground begins releasing heat accumulated during the day.
Under favourable conditions, the ground and nearby surfaces can cool rapidly.
This process is known as radiational cooling.
Clear Skies
Clouds can help retain heat near the Earth’s surface.
When skies are clear, more heat can escape into the atmosphere.
This can allow surface temperatures to decrease more quickly.
Calm or Light Winds
Strong winds mix warmer and colder layers of air.
When winds are calm or light, colder air can settle near the ground and create favourable conditions for frost.
Local Terrain
Cold air is denser than warm air and can move into valleys and low-lying areas.
These locations may experience colder temperatures than nearby higher elevations.
What Are the Different Types of Frost?
Several types of frost can develop depending on temperature, moisture and weather conditions.
Radiation Frost
Radiation frost commonly develops on clear, calm nights.
The ground loses heat, causing surfaces and nearby air to cool.
This is one of the most common types of frost affecting gardens and crops.
Hoar Frost
Hoar frost forms when water vapour changes directly into ice crystals on cold surfaces.
It often creates a visible white coating on grass, plants, trees and other objects.
Advection Frost
Advection frost occurs when cold air moves into an area.
Unlike radiation frost, advection frost may be associated with stronger winds and a larger mass of cold air.
Ground Frost
Ground frost occurs when the surface temperature falls below freezing.
Frost may develop on grass and other surfaces even when the officially measured air temperature remains slightly above 0°C.
Frost Advisory vs Extreme Cold Warning
A Frost Advisory and Extreme Cold Warning communicate very different cold-weather hazards.
A Frost Advisory is primarily issued because of the potential for damage to frost-sensitive plants and crops during the growing season.
An Extreme Cold Warning is issued when dangerously cold temperatures or wind chills create a serious risk to human health.
An Extreme Cold Warning generally communicates a significantly greater threat to people than a Frost Advisory.
Learn more about what an Extreme Cold Warning means in Canada.
Frost Advisory vs Freezing Drizzle Advisory
A Frost Advisory and Freezing Drizzle Advisory involve different weather conditions and hazards.
A Frost Advisory indicates that cold temperatures may cause frost and damage sensitive plants and crops.
A Freezing Drizzle Advisory indicates that freezing drizzle may create icy surfaces and hazardous travel conditions.
Learn more about what a Freezing Drizzle Advisory means in Canada.
Frost Advisory vs Snowfall Warning
A Frost Advisory and Snowfall Warning communicate different weather hazards.
A Frost Advisory focuses on cold temperatures and the potential for frost damage to plants and crops.
A Snowfall Warning indicates significant falling snow that is expected to create hazardous conditions and potentially significant impacts.
Frost may occur without any precipitation.
Learn more about what a Snowfall Warning means in Canada.
Frost Advisory vs Winter Storm Warning
A Frost Advisory focuses specifically on the risk of frost damage to vulnerable vegetation.
A Winter Storm Warning may involve a combination of significant winter weather hazards, including snow, freezing rain, strong winds and blowing snow.
A Winter Storm Warning generally communicates a greater potential risk to transportation, infrastructure and daily activities.
Learn more about what a Winter Storm Warning means in Canada.
Can a Frost Advisory Become a Warning?
Canada does not use a separate Frost Warning as part of its standard public weather alert system.
If other hazardous cold-weather conditions develop, Environment and Climate Change Canada may issue the appropriate alert for that specific hazard.
For example, an Extreme Cold Warning may be issued when dangerously cold temperatures or wind chills create a serious health risk.
A Frost Advisory does not automatically become an Extreme Cold Warning because the two alerts communicate different hazards and are issued for different reasons.
People should continue monitoring current weather information when temperatures are expected to change.
What Can Happen During a Frost Advisory?
The impacts of a Frost Advisory depend on temperature, duration and the sensitivity of affected vegetation.
Garden Plants Can Be Damaged
Frost-sensitive garden plants may experience damage when exposed to sufficiently cold temperatures.
Leaves, flowers and stems may become damaged.
Crops Can Be Affected
Agricultural crops may experience frost damage.
The seriousness of the impact depends on the crop, stage of development, temperature and duration of exposure.
Flowers and Buds Can Be Damaged
Fruit trees and other flowering plants may be particularly vulnerable when frost occurs after buds or flowers have developed.
Damage during this stage may affect future fruit production.
Young Plants Can Be Killed
Seedlings and recently planted vegetation may be particularly vulnerable to frost.
Some young plants may not survive significant exposure to freezing temperatures.
Agricultural Losses Can Occur
Significant frost events may result in reduced crop yields and financial losses for agricultural producers.
What Should You Do During a Frost Advisory?
The appropriate response depends on the plants, crops and local conditions.
Read the Complete Advisory
Read the complete alert to understand the expected temperatures, timing, affected locations and recommended actions.
Protect Frost-Sensitive Plants
Cover vulnerable plants before temperatures fall.
Blankets, frost cloths and other appropriate coverings may help protect vegetation from cold conditions.
Move Potted Plants Indoors
When possible, move frost-sensitive potted plants into a garage, shed or indoor location.
Monitor Local Temperatures
Temperatures can vary significantly between locations.
Low-lying areas may become colder than surrounding locations.
Follow Agricultural Recommendations
Farmers and commercial growers should follow appropriate frost protection practices for their crops and region.
Monitor Current Weather Information
Continue checking current weather information while the advisory remains in effect.
Environment and Climate Change Canada provides official weather forecasts and alerts for communities across Canada.
How Do You Protect Plants From Frost?
Several methods may help protect vulnerable plants from frost.
Cover Vulnerable Plants
Covering plants can help reduce heat loss.
Frost cloths, blankets and other appropriate materials may provide protection.
Avoid placing heavy materials directly on delicate plants when they may cause damage.
Move Containers Indoors
Potted plants can often be moved into garages, sheds or other protected locations.
Water Plants Before Frost
Moist soil can retain more heat than very dry soil.
Depending on the plant and conditions, watering before a frost event may help moderate soil temperatures.
Use Mulch
Mulch can help insulate the soil and protect plant roots from temperature changes.
Choose Appropriate Planting Locations
Protected locations near buildings or other structures may sometimes experience warmer conditions than open and exposed areas.
What Temperature Causes Frost?
Frost can develop when surface temperatures fall to or below freezing.
However, frost may sometimes occur even when the officially measured air temperature remains slightly above 0°C.
This is because temperatures near the ground and on exposed surfaces can be colder than temperatures measured at standard weather station height.
The risk of plant damage depends on more than a single temperature.
The duration of the cold, plant species and stage of growth also influence the potential impacts.
What Is the Difference Between Frost and a Freeze?
Frost and a freeze are related but different.
Frost refers to ice crystals that develop on surfaces under appropriate temperature and moisture conditions.
A freeze occurs when air temperatures fall to or below 0°C.
Frost may sometimes develop even when officially measured air temperatures remain slightly above freezing because surfaces near the ground can become colder.
A freeze can also occur without visible frost when the air is sufficiently dry.
Can Frost Occur Above 0°C?
Yes.
Frost can sometimes develop when the officially measured air temperature is above 0°C.
Weather station temperatures are generally measured above the ground.
Grass, plants and other surfaces may become colder than the surrounding air, particularly on clear and calm nights.
This means surface temperatures can fall below freezing even when the reported air temperature remains slightly above 0°C.
How Long Does a Frost Advisory Last?
There is no standard duration for a Frost Advisory.
The length of the advisory depends on temperature, weather patterns, local conditions and the expected risk to plants and crops.
Some Frost Advisories may remain in effect overnight.
Others may continue through multiple nights when cold conditions persist.
The advisory generally ends when temperatures are no longer expected to create a significant frost risk.
When Are Frost Advisories Issued in Canada?
Frost Advisories are generally issued during the growing season when cold temperatures may damage vulnerable plants and crops.
The timing of the growing season varies significantly across Canada.
Southern regions may have longer growing seasons, while northern and higher-elevation areas may experience shorter periods between the last spring frost and first fall frost.
Frost Advisories may be particularly common during spring and fall when temperatures can change significantly.
How Can You Check Current Frost Advisories?
Current Frost Advisories and other weather alerts can be checked through Environment and Climate Change Canada’s official weather services.
The official Weather Information map allows users to check current forecasts and weather alerts across Canada.
The Government of Canada’s WeatherCAN application also provides official forecasts, alerts and customizable notifications.
Frequently Asked Questions About Frost Advisories
A Frost Advisory means frost is expected during the growing season and may damage or kill frost-sensitive plants and crops.
A Frost Advisory is primarily a concern for gardeners, farmers and people responsible for vulnerable plants. Significant frost may damage crops and vegetation.
There is no single temperature that applies to every situation. Frost risk depends on temperatures near the ground, weather conditions, location and the vulnerability of plants and crops.
Yes. Surfaces near the ground may fall below freezing even when the officially measured air temperature remains slightly above 0°C.
Frost refers to ice crystals that form on surfaces. A freeze occurs when air temperatures fall to or below 0°C.
Protecting frost-sensitive plants may reduce the risk of damage. Appropriate coverings or moving potted plants into protected locations may help.
A Frost Advisory does not automatically become an Extreme Cold Warning. The alerts communicate different hazards and are issued for different reasons.
Sources
- https://www.canada.ca/en/services/environment/weather/severeweather/weather-alerts.html
- https://www.canada.ca/en/services/environment/weather/severeweather/weather-alerts/weather-impact-guides.html
- https://weather.gc.ca/
- 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