The short answer
| Alert | What it means | What to do |
|---|---|---|
| Winter storm watch | A significant storm is possible, usually 12 to 48 hours away | Prepare. Check supplies and plans |
| Winter weather advisory | Snow, sleet or ice is expected and will be a nuisance | Take care. Allow extra travel time |
| Winter storm warning | A dangerous storm is happening or imminent | Act. Avoid travel and stay safe |
These are the terms used by the US National Weather Service (NWS). Canada, the UK and other countries use similar tiers with different names, covered below.
Watch: get ready
A winter storm watch is issued when the ingredients for a significant storm are in place, but the timing, track or amounts are still uncertain. It usually comes 12 to 48 hours ahead.
A watch is a heads-up, not a forecast of certainty. Use it to:
- Check your power-outage supplies: torches, batteries, charged power banks, food and water.
- Fill prescriptions and buy essentials before shops get busy.
- Protect plumbing that freezes easily. See how to prevent frozen pipes.
- Fuel the car and move it somewhere a snowplough will not bury it.
A watch is later upgraded to a warning or advisory, or cancelled.
Advisory: be careful
A winter weather advisory means winter weather is expected that is inconvenient and can be hazardous, but does not reach warning level. Typical triggers are a few inches of snow, some sleet, or a light glaze of freezing rain.
Advisories cause many accidents, because people treat them as minor. Slow down, leave more distance, and expect slippery pavements and roads, especially on bridges and in the early morning.
Warning: take action
A winter storm warning means heavy snow, sleet or ice is occurring or very likely, and conditions will be dangerous. Travel may become impossible, and power cuts are more likely.
- Stay off the roads unless it is an emergency.
- Keep devices charged and know where your torches are.
- Check on neighbours, especially older people and people who live alone.
- Never use generators, grills or camp stoves indoors, or in a garage, even with the door open. They produce carbon monoxide, a leading cause of death after winter storms.
Typical thresholds
Each local NWS office sets its own criteria, because 3 inches of snow paralyses Atlanta but barely registers in Buffalo. These are typical benchmarks in the snowier parts of the US:
| Alert | Snow | Ice |
|---|---|---|
| Advisory | A few inches, below the local warning level | Any freezing rain, under ¼ inch |
| Warning | About 4 to 6 inches or more in 12 hours, or 6 to 8 inches or more in 24 hours | ¼ inch or more of ice |
Southern states often use 2 inches for a warning, while mountain areas may use 12 inches or more. Your local NWS office publishes its criteria.
Other winter alerts
- Blizzard warning: sustained winds or frequent gusts of 35 mph or more, with falling or blowing snow that cuts visibility to under a quarter of a mile, for at least 3 hours. A blizzard is about wind and visibility, not the amount of snow.
- Ice storm warning: a damaging build-up of freezing rain, usually ¼ inch or more, which brings down trees and power lines.
- Extreme cold warning and cold weather advisory: dangerously cold temperatures or wind chills. These replaced the older "wind chill" warnings and advisories in the NWS system in 2024.
- Lake effect snow warning: heavy, localised bands of snow downwind of the Great Lakes.
Outside the US
- Canada: Environment Canada issues special weather statements, advisories, watches and warnings for snowfall, freezing rain, blizzards and extreme cold.
- UK: the Met Office uses yellow, amber and red warnings for snow and ice, based on both the likelihood and the impact.
- Europe: most national weather services feed the Meteoalarm system, with yellow, orange and red levels.
The principle is the same everywhere: the higher the level, the more you should change your plans.
Where to get alerts
- Your phone: government emergency alerts (Wireless Emergency Alerts in the US) are on by default. Check they are enabled in your notification settings.
- The NWS website, weather.gov, by entering your postcode or ZIP code.
- NOAA Weather Radio, which works when mobile networks are down.
For summer, the equivalent guide is our explainer on extreme heat watches and warnings.
Key takeaways
- Watch = possible, prepare. Advisory = expected and inconvenient, take care. Warning = dangerous, act.
- Thresholds vary by region, so a warning in the South may mean just 2 inches of snow.
- Blizzards are defined by wind and visibility, not snowfall.
- Never run a generator or grill indoors during a storm.