Freeze Warning vs Frost Advisory: what each one means

A Freeze Warning means temperatures of 32°F (0°C) or lower are expected over a wide area for long enough to kill sensitive vegetation, typically several hours in the pre-dawn. A Frost Advisory covers the milder case: air temperatures of about 33 to 36°F on a clear, calm night, when frost forms on surfaces even though the thermometer never reaches freezing. A Hard Freeze Warning is the severe case, usually 28°F or lower, cold enough to kill hardy plants and damage exposed pipes. Roughly 248,000 Americans a month search "freeze warning", concentrated in October and April. Every US city page here shows the live NWS alerts next to the 10-day lows, so you can see how many cold nights are coming, not just tonight's.

Why it says frost at 36 degrees

Official temperature is measured about 5 feet above the ground, in a ventilated shelter. On a clear, windless night the ground radiates heat to space and the air in the bottom few inches gets several degrees colder than the thermometer. Grass, windshields and tomato leaves sit in that layer. So a forecast low of 35°F can produce a white lawn and a scraped windshield, and a Frost Advisory is the office telling you that the surface will freeze even if the air does not. Cloud cover or wind spoils the effect, which is why frost nights are the still, starry ones.

The three products, side by side

• Frost Advisory: 33 to 36°F with clear skies and light wind. Tender plants (tomatoes, peppers, basil, annual flowers) are at risk. Cover them or bring them in.
• Freeze Watch: a freeze is possible in the next 24 to 48 hours. This is the product that gives you a full day to act.
• Freeze Warning: 32°F or lower expected. Unprotected tender plants die; semi-hardy plants are damaged. Drain and disconnect garden hoses, cover outdoor faucets, bring pets in.
• Hard Freeze Warning: about 28°F or lower for several hours. Hardy plants and most unharvested produce are lost, and exposed pipes in unheated spaces can burst. Criteria vary by office; some use 27°F.

Only during the growing season

This is the part that confuses people every year. Freeze and frost products are issued only between the last freeze of spring and the first freeze of autumn, because their purpose is to protect crops and gardens. Once the local growing season is declared over, usually after the first widespread hard freeze, the office stops issuing them until spring, even if it drops to 20°F in January. Winter cold gets a different set of products: since October 2024 the Cold Weather Advisory and the Extreme Cold Warning, which replaced the old wind chill advisory and warning. Wind chill vs feels like explains how those are measured.

In the Deep South, Florida, coastal California and the desert Southwest, where citrus, avocados and winter vegetables grow through the winter, the growing season never closes and freeze warnings run all year.

What to do the evening before

• Plants: water the soil in the afternoon (moist soil holds heat), then cover with fabric sheets or frost cloth that reaches the ground, not plastic touching the leaves. Remove covers in the morning. Potted plants go inside or against a south-facing wall.
• Pipes and hoses: disconnect hoses, cover hose bibs, and on a Hard Freeze Warning let a faucet drip in unheated areas and open cabinet doors under sinks on exterior walls.
• Pets and people: bring animals in. Check on neighbors who heat with space heaters.
• Cars: a Freeze Warning is a scraped windshield in the morning. Ten minutes matters if you have an early commute.

Reading the low temperature forecast

Overnight lows are where forecast models split the most in autumn, because the difference between 31°F and 35°F is a cloud deck arriving an hour earlier or a breeze that never dies. On our city pages, Minneapolis or Atlanta for example, the NWS blend, the American GFS and the European model show their lows side by side for the next 14 days, and our accuracy scoreboard shows which one has been closest in your city. When two models say 34 and one says 30, cover the tomatoes.

Advisories, watches and warnings share one grammar across every hazard; watch vs warning, and what the difference means is the starting point, and how to get weather alerts on your phone explains why freeze warnings never arrive as a push alert unless you set one up.