Frost Advisory vs Freeze Warning: What Each One Means

Direct answer: a Frost Advisory means the US National Weather Service expects overnight lows of about 33 to 36°F on a clear, calm night — cold enough for frost to form on plants even though the air stays just above freezing. A Freeze Warning means lows of 32°F or colder, cold enough to kill many crops and garden plants. A Freeze Watch comes first: a freeze is possible in the next 12 to 48 hours. All three are about plants, not people, and all three stop once your area’s growing season has ended.

Frost advisory, freeze watch, freeze warning

• Frost Advisory — be aware. Minimum temperatures forecast at 33 to 36°F on a night with light winds and clear skies. Frost is expected or occurring and threatens sensitive vegetation.
• Freeze Watch — be prepared. Conditions are favourable for a freeze that would meet warning criteria in the next 12 to 48 hours.
• Freeze Warning — take action. Minimum temperatures forecast at 32°F or lower. The NWS notes that below 32°F for a long period kills some commercial crops and garden plants, and below 28°F for an extended period can kill most of them. A warning for that colder case may be worded as a hard freeze.

How can there be frost when it is above freezing?

Because the official temperature is measured in a shelter about head height above the ground, not at the ground. On a clear night with little wind, the ground, grass and leaves lose heat straight to the sky and can drop below freezing while the air a couple of metres up is still at 34 or 35°F. That is why the frost advisory sits above 32°F, and why the NWS only issues it on nights with good radiational cooling: clouds or a breeze keep the surface from cooling that far.

Why the advisories stop later in the autumn

Every one of these products is issued only during the locally defined growing season. Each National Weather Service office defines when that season ends for its area. After that the office stops issuing frost advisories and freeze warnings, even on nights that are colder, because there is nothing left growing to protect. So if your neighbours further south are still getting freeze warnings and you are not, it usually means your season has already been called over, not that it is warm.

In spring the same products return at the start of the growing season, when a late frost can kill new growth and blossom.

What to do

1. Frost Advisory: cover tender plants overnight, or bring potted plants indoors.
2. Freeze Watch: plan to do the same and more — the following night may be colder.
3. Freeze Warning: protect or harvest what you can before evening. Plants left uncovered at 32°F or below for hours may not survive.

None of these is a warning about people. For dangerous cold — wind chill, extreme cold — the NWS issues separate cold weather advisories and extreme cold warnings. Our cold weather safety guide covers those.

Where to check

• weather.gov — enter your town; active frost and freeze products are listed at the top of the forecast.
• Your phone’s weather app usually shows them too. Tap through to the full text for the hours and counties it covers; our article on weather apps and official warnings explains why the summary can differ.

How this site shows them

Our US weather alerts by state list the National Weather Service warnings it rates severe or extreme. A freeze warning is rated severe, so it appears there; a frost advisory is rated minor, so it does not — check weather.gov for those. This site does not issue warnings; the National Weather Service does.

Related reading: alert levels and colour codes around the world and cold waves.

Frequently asked questions

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

A frost advisory means overnight lows of about 33 to 36 F on a clear, calm night, so frost forms on plants. A freeze warning means lows of 32 F or colder, cold enough to kill many crops and garden plants.

What temperature is a frost advisory?

The National Weather Service issues a frost advisory when minimum temperatures are forecast at 33 to 36 F on a night with light winds and clear skies, during the local growing season.

Why is there frost when the temperature is above freezing?

The official temperature is measured about head height above the ground. On clear, calm nights the ground and plants lose heat to the sky and can fall below freezing while the air above is still 34 or 35 F.

Why did frost advisories stop in my area?

Frost and freeze products are issued only during the locally defined growing season. Once your forecast office ends the season for your area, it stops issuing them even on colder nights.

Sources

• NWS Instruction 10-515 - Non-precipitation weather products (16 May 2025)
• US National Weather Service - Understanding cold weather watches, warnings and advisories

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