NOAA Storm Prediction Center
The Storm Prediction Center is tasked with forecasting the risk of convective severe weather in the contiguous United States, and issues convective outlooks, mesoscale discussions, and watches as a part of this process. Convective outlooks are issued for day 1, day 2, day 3, and day 4-8, and detail the risk of severe thunderstorms and tornadoes during the given forecast period. Mesoscale discussions are issued to give information on a region that is becoming a severe weather threat and states whether a watch is likely and details thereof, as well as situations of isolated severe weather when watches are not necessary. Watches are issued when forecasters are confident that severe weather will occur, and usually precede the onset of severe weather by 1 hour.