What Is a Frost Advisory? A Guide for Canadian Farmers

A frost advisory is a public weather alert warning that overnight temperatures are expected to fall low enough for frost to form and damage sensitive plants. In Canada, Environment and Climate Change Canada (ECCC) issues frost advisories mainly during the growing season, when a frost can hurt crops, gardens and orchards. The exact criteria vary by region, because what counts as a damaging frost depends on the local growing season, so always read the alert text for your area.

Frost, Freeze and What the Thermometer Misses

Frost is ice crystals forming on surfaces that have cooled to 0°C or below. Frost can form on crops even when the reported air temperature stays a degree or two above freezing, because official temperatures are measured above the ground, while leaves and low-lying ground cool faster than the air above them on clear, calm nights. A freeze usually refers to the air temperature itself falling below 0°C, which tends to damage a wider range of crops. Terminology differs between countries: in the United States, for example, forecasters use separate frost advisories and freeze warnings.

Why Some Fields Get Hit Harder

Which Crops Are Most at Risk

Frost damage depends on the crop, its growth stage, how cold it gets and for how long. As a general rule, crops are most vulnerable while emerging, flowering or filling seed, and warm-season crops such as corn, soybeans, dry beans and many vegetables are more sensitive than cool-season cereals. Provincial crop specialists publish stage-specific frost guidance for major crops, and it is worth keeping the guide for your province close during spring and fall.

What to Do When a Frost Advisory Is Issued

Regional Advisories vs Farm-Level Frost Alerts

Public advisories cover a forecast region, and a single region can include very different terrain. A farm-level alert looks at the forecast for your farm's coordinates instead. Both are useful, and neither replaces checking conditions in your own fields.

Advisory, Watch or Warning — and What the Colours Mean

Environment and Climate Change Canada updated the public alert system in February 2026, and every alert now carries a colour alongside its type. Yellow means hazardous weather may cause damage, disruption or health impacts that are moderate, localized or short-term — this is the level most frost alerts are issued at, and it is the most common alert level. Orange means severe weather is likely to cause significant, widespread damage, and is uncommon. Red means very dangerous and possibly life-threatening weather, and is rare. Warnings, advisories and watches all receive a colour when issued.

For a farm, the practical difference between the labels matters less than the timing and the location. An advisory issued for your forecast region at eight in the evening is a prompt to check your own low fields, not a measurement of them.

What Temperature Does Frost Form At?

Frost forms when a surface cools to 0°C or below and water vapour freezes onto it. The important word is surface. Official air temperatures are measured in a shelter roughly 1.25 to 2 metres above the ground, so on a clear, calm night the crop canopy and the soil surface can sit two to four degrees colder than the number in the forecast. This is why frost is regularly reported on mornings when the official low was 2°C or 3°C, and why a forecast of 2°C is not a safe margin for a sensitive crop.

Frequently Asked Questions

What temperature triggers a frost advisory in Canada?

There is no single national number. Environment and Climate Change Canada sets alert criteria by region, generally around temperatures near or below freezing during the growing season. Read the alert text for your area and check ECCC's public weather alerts for the current criteria.

Can frost form when the temperature is above 0°C?

Yes. Official temperatures are measured above the ground. On clear, calm nights, leaves and low spots can cool to freezing while the air above is still slightly warmer, so frost can form even when the reported low is a little above 0°C.

How soon can I see frost damage on crops?

Often not right away. Frost-damaged tissue can take several days to show wilting, discolouration or water-soaked patches, so it is usually worth waiting a few days before judging how much of a crop was affected.

What is the difference between a frost advisory and a frost warning?

Both mean frost is expected; the label reflects how severe the expected impact is. An advisory covers conditions worth acting on that fall short of warning-level severity, while a warning signals an event significant enough to cause real damage. Since February 2026 each alert also carries a colour — yellow, orange or red — showing the expected level of impact. Neither label tells you the temperature in a specific field.

What does a yellow frost alert mean?

Yellow is the lowest of the three colours in Canada's alert system. It means hazardous weather may cause damage, disruption or health impacts that are moderate, localized or short-term. Most frost alerts are issued at this level, and for a farm it is a prompt to check the most frost-prone fields rather than a signal to ignore.

Does AgriIntel replace Environment Canada alerts?

No. AgriIntel's frost alerts are based on a forecast for your farm's coordinates and are a planning aid. Keep following official ECCC weather alerts for your region.