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Watch versus a warning - what's the difference?

The NWS issues both watches and warnings when weather conditions/events

threaten life and/or property. This includes watches and/or warnings for winter storms, hurricanes and tropical storms, tornadoes and severe thunderstorms, flash floods, high wind, fire weather, freezing rain/drizzle, wind chill and blizzards just to name a few. Additionally, the NWS issues advisories for weather events that are less serious than a watch or warning, but may cause significant inconvenience. An example is a winter weather advisory. If caution is not exercised, it could lead to situations that may ultimately threaten life and/or property. When issuing watches or warnings the NWS generally uses a three-tiered approach as shown in the diagram below.

This approach is largely based on two variables, time until the event and certainty of the event. Outlooks are issued well in advance of the event when conditions are ordinarily uncertain. For example, the Storm Prediction Center (SPC) may issue a severe thunderstorm outlook three or more days in advance of the severe thunderstorm event. The outlook area will typically cover a large geographic region as shown by the purple line in the diagram below.