You hear the terms on the news or radio all the time – “Severe Thunderstorm Watch”, “Winter Storm Warning”, “Freeze Watch”. But what do these phrases actually mean, and what is the difference between them?
Watches, warnings, and advisories are all issued by the National Weather Service. Each individual NWS office issues its own weather statements.
A watch is the first type of weather statement to be issued before an upcoming weather event. A watch means that the weather is expected to occur in the given area. For example, a Winter Storm Watch means that wintry conditions are expected to occur. This can mean snow, freezing rain, sleet, or a combination, depending on the area of the country the watch is issued for. The criteria for a Winter Storm Watch, Freeze Watch, etc. is different in New York City as opposed to in Charlotte, NC. Watches are issued up to 48 hours in advance of the impending weather. They are generally upgraded to either warnings or advisories, depending on the severity of the weather event.
A warning means the weather is about to arrive or is already happening. A Severe Thunderstorm Warning or Tornado Warning is issued when an NWS office notices that a severe thunderstorm or tornado has formed, which they can detect by looking at Doppler radar. A Winter Storm Watch will be upgraded to a Winter Storm Warning once the storm is imminent. A Flood Watch may be issued before a heavy rainfall. A Flood Warning may then be issued as rivers and streams are flooding during the rain event.
An advisory also means the weather is about to arrive or is already happening. Watches are often upgraded to advisories rather than to warnings. An advisory is a milder statement compared to a warning. A Winter Weather Advisory means wintry weather will occur, but is used for a lesser event (less snowfall/ice) as compared to a Winter Storm Warning. An Excessive Heat Watch will be upgraded to a Heat Advisory if temperatures will be high, but upgraded to an Excessive Heat Warning if they will be very high.
Simply put, a watch means to be on the lookout for inclement weather that may be occurring in the next day or two. A warning or advisory means the weather is about to occur or is already here, so take any necessary precautions.