What Is a Frost Advisory?
A Frost Advisory is issued by Environment and Climate Change Canada (ECCC) when temperatures are expected to fall low enough during the growing season for frost to form and potentially damage frost-sensitive plants and crops.
Frost can develop even when the forecast air temperature remains slightly above 0°C because surfaces near the ground can cool more quickly than the surrounding air.
When Is a Frost Advisory Issued in Canada?
A Frost Advisory may be issued during the growing season when temperatures are expected to approach freezing and conditions are favourable for frost formation.
Meteorologists look at forecast temperatures, humidity, cloud cover, wind and how quickly temperatures are expected to fall overnight. Clear skies and light winds can increase the risk because they allow heat near the ground to escape more efficiently.
The growing season varies considerably across Canada, so the timing of Frost Advisories also differs by region. They are generally most common around the beginning and end of the local growing season.
Read More: How Do Meteorologists Predict Frost?
What to Expect During a Frost Advisory
Temperatures near the ground may fall to around the freezing point, allowing frost to form on exposed surfaces.
Frost is most likely overnight and around sunrise, when temperatures are typically at or near their lowest. Low-lying and sheltered areas can sometimes become colder than surrounding locations, so frost may develop unevenly across a region.
A Frost Advisory does not necessarily mean every location within the advisory area will experience frost.
How Frost Can Affect Plants and Crops
Frost can damage sensitive vegetation when ice forms on or within plant tissue. The amount of damage depends on the temperature, how long cold conditions last and the type and growth stage of the plant.
Young plants, flowers, vegetable gardens and some fruit crops can be particularly vulnerable. A brief light frost may cause limited damage, while colder or longer-lasting conditions can result in more significant losses.
What to Do When a Frost Advisory Is Issued
Bring potted plants indoors when possible and cover frost-sensitive outdoor plants before temperatures fall. Covers can help retain some of the heat stored in the ground around the plant.
Gardeners and growers should pay attention to the expected overnight low and local conditions, since temperatures can vary over relatively short distances.
Check the latest forecast for your area to see when the coldest temperatures are expected and when conditions should begin to improve.
Learn More
- Frost: A layer of ice crystals that forms on surfaces when conditions near the ground become cold enough.
- Freezing Temperature: Temperatures at or below the freezing point of water.
Frequently Asked Questions
Frost commonly becomes a concern as temperatures approach 0°C, but frost can sometimes form when the official air temperature is slightly above freezing because surfaces near the ground may be colder.
No. A Frost Advisory means conditions are favourable for frost that could damage sensitive plants and crops. Frost formation can vary within the advisory area.
Frost-sensitive flowers, vegetables, young plants and other tender vegetation should be protected. Potted plants can be moved indoors when possible.
Frost is most likely overnight and around sunrise, particularly when skies are clear, winds are light and temperatures are near freezing.
Frost Advisories are generally issued during the local growing season when temperatures are expected to become cold enough for frost to pose a risk to plants and crops.
