During times of severe weather, the National Weather Service uses a variety of notifications to alert residents to potentially hazardous conditions, but the two main tools that they use are watches and warnings.
There is some confusion about what those terms mean, but here is how the NWS uses those two alerts.
Watches
A watch is issued when conditions are such that a severe weather event, such as a severe thunderstorm, a tornado or a winter event like a blizzard, is possible.
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Watches tend to be widespread over large areas, as the NWS uses them when the forecasted movement and location of a storm system is still uncertain.
When watches are issued, residents are urged to keep an eye on the forecast, and to prepare for the possibility of severe weather, taking extra precautions as needed.
Warnings
Local
A warning is issued when a severe weather event is actively taking place. That can include a severe thunderstorm or a tornado, whether that tornado has been observed by trained weather spotters or has appeared as rotation on Doppler radar.
In the event of a warning, residents are urged to take shelter immediately, preferably in an interior room of a structure or in the basement if possible.
