Weba severe thunderstorm warning is issued by the nws when a storm is capable of producing wind gusts of at least 58 mph and/or hail at least 1 inch in diameter. Webfor example, a severe thunderstorm watch means that a severe thunderstorm is expected in the next six hours or so within an area approximately 120 to 150 miles wide and 300 to. Weba severe thunderstorm watch means that atmospheric conditions are favorable for severe thunderstorm development. The severe thunderstorm watch. Websevere thunderstorms are dangerous weather events that require vigilance and preparedness. Understanding the difference between a severe thunderstorm.