Warning Guide
What each official warning means, in plain words, with the service that defines it.
These are summaries for reading the live wall. The issuing service's own definition always wins; each section links to it.
Watch, warning, advisory
| Level | United States (NWS) | Canada (ECCC) |
|---|---|---|
| Watch | Conditions are favorable for the hazard to develop. Be ready. | Conditions are favorable. Stay alert. |
| Warning | The hazard is happening or about to, in the warned area. Act. | Hazardous weather is happening or about to. Take action. |
| Advisory | Less serious conditions that still cause trouble. | Specific conditions below warning level (for example frost). |
Europe: MeteoAlarm colours
| Colour | Meaning |
|---|---|
| Green | No particular awareness of the weather is required. |
| Yellow | Potentially dangerous weather. Be aware. |
| Orange | Dangerous weather. Be prepared. |
| Red | Very dangerous weather. Take action. |
Source: EUMETNET – MeteoAlarm, meteoalarm.org.
Thunderstorm
A Severe Thunderstorm Warning (US) is issued for storms producing hail one inch or larger or wind gusts of 58 mph or more. The warning text often states the expected hail size and gust. Live thunderstorm wall.
Hail
There is no separate US hail warning: hail is carried inside the Severe Thunderstorm Warning, which lists a hail size. PerilRadar shows hail in three layers: the warning as issued, the radar estimate, and the ground reports. Live hail wall.
Wind
A High Wind Warning (US) covers damaging winds not caused by a thunderstorm. Local offices set the thresholds. Live wind wall.
Tornado
A Tornado Watch covers a broad area where tornadoes are possible. A Tornado Warning means a tornado has been seen or indicated by radar. Go to shelter when a warning covers you. Live tornado wall.
Hard freeze
A Freeze Warning (US) is issued when temperatures are expected to fall low enough to kill crops and sensitive plants. The older Hard Freeze Warning name has been folded into it. A Frost Advisory is the milder step. Live freeze wall.
Lightning
Lightning has no warning product of its own in the US; it is part of every thunderstorm. The advice from the National Weather Service: when thunder roars, go indoors. Live lightning maps.
Sources: NOAA / National Weather Service product definitions; Environment and Climate Change Canada alert types; EUMETNET – MeteoAlarm.
Common questions
What is the difference between a watch and a warning?
In the United States and Canada, a watch means conditions are favorable for the hazard to develop. A warning means it is happening or about to happen in a specific area. Advisories cover less serious but still hazardous conditions.
What do the MeteoAlarm colours mean?
MeteoAlarm shows European warnings in four levels. Green means no particular awareness is needed, yellow means be aware, orange means be prepared, and red means take action.