The National Weather Service also staffs the Storms Prediction Center in Norman, Oklahoma, which forecasts and tracks severe weather -- as in tornadoes -- for the entire U.S. They are responsible for issuing tornado watches, although the local NWS offices issue severe thunderstorm and tornado warnings.
The SPC also does long range forecasting to model when and where the worst severe weather is likely to hit. Their convective outlooks help keep residents aware of the possibility of severe weather and keep them prepared for it.
Of all the government agencies in existence, the National Weather Service is certainly one of the most useful.