Tornadoes occur over a wide spectrum of strengths, sizes, and lifetimes. On the other end of the tornado spectrum are strong and violent tornadoes. Such tornadoes may last for as little as 10 min to over 2 h in extreme cases and may be produced in cyclic fashion from the same thunderstorm. Watches serve to fine-tune forecast areas already identified in severe weather outlooks. Tornado warnings are issued for storms that are known to include or are thought highly likely to include a tornado.
Warnings indicate a high probability of imminent danger.
Both products are accompanied by discussions describing the type, coverage, and intensity of the severe weather expected. On days when the threat of tornadoes is particularly high and the activity may cover a significant portion of the country, the SPC also issues a special Public Severe Weather Outlook. Tornado watches are issued by the NWS when conditions are favorable for the development of tornadoes. Watches are an important part of the tornado alert system as they set into motion the necessary procedures to deal adequately with detection, tracking, warning, and response. Tornado watches are issued in advance of expected storm development to alert the public to the potential of severe weather so that they will be ready to seek shelter if a warning is subsequently issued.