When it comes to severe weather advisories, a warning is more severe than a watch. Each is issued by a different branch of the U.S. National Oceanic and Atmospheric Administration.
According to Dan Kottlowski, a senior meteorologist for AccuWeather, the Storm Predictor Center issues watches when current conditions are favorable for severe weather – often a thunderstorm or a tornado – but watches don't necessarily mean that the weather is imminent. Watches also tend to cover much broader geographical areas, often up to 25,000 square miles.
Warnings are issued by local offices of the National Weather Service and occur when severe weather is imminent. Officials issue a warning when specific criteria, such 1-inch hail and 55-mph winds, have been confirmed in an area.