What is the Difference Between a Weather Watch and Warning?

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Spring not only brings warmer weather, but it also brings on storm season which means the news will be filled with weather advisories, watches and warnings.

Although these terms all refer to active weather events, their meaning and severity are different.

What is a weather advisory?

Weather advisories can be used to cover a wide array of weather conditions.

These bulletins are often issued preceding watches and warnings, or they can be issued to indicate severe weather in a long-term forecast. 

What is a weather watch?

Watches are issued when there is the potential for severe weather.

When conditions favour that severe weather is forming, a watch will be released to make the public aware of what could happen. 

What is a weather warning?

A warning is the next step in the process.

Warnings are issued when that severe weather is actually occurring or is imminent.

For example, a thunderstorm watch means there is a good chance that a storm will occur in the affected area, whereas a thunderstorm warning would mean a storm is occurring or about to occur.

What are the criteria?

There are a specific set of criteria a storm must reach to require the issuance of a warning.

A severe thunderstorm watch will be issued if there is the potential for the development of a thunderstorm with either wind gusts of 90 km/h or greater, hail with a diameter of two centimetres or greater, or heavy rainfall (with 50 millimetres or more within one hour).

A warning is issued if a cell is spotted on radar with one or more of those weather conditions occurring. 

Visit the government of Canada’s webpage that lists public weather alerts for each province and territory to stay informed.