The National Weather Service (NWS) is an agency of the United States government which is focused on providing weather forecasts and warnings to the government, industry, and individuals. It is part of a larger government agency, the National Oceanic and Atmospheric Administration (NOAA). The mission of the National Weather Services includes a focus on weather safety, monitoring of climate change, and protection of the American economy with accurate and timely forecasts about upcoming weather events which could threaten American industry.
The earliest version of the National Weather Service was founded in 1870, as the National Weather Bureau. In 1967, the NWS acquired its current name, as part of a general reorganization scheme in the government which led to the establishment of the NOAA. Thanks to the long history of the National Weather Service, it is possible to look at weather data dating back to 1870 in many parts of the United States, and for some regions, this data is much older.
As you might imagine, one of the major tasks of the National Weather Service is providing weather forecasts. The NWS also offers hydrological forecasts which include flood warnings, information about changing water levels, and so forth. A number of forecasts are customized for particular areas of concern. For example, the National Weather Service offers aviation forecasts, with data which would be relevant to pilots, along with marine forecasts and fire weather forecasts which look at conditions which might increase the risk of fire or make a fire difficult to fight.
For the Southern states, the National Weather Service maintains the National Hurricane Center, which monitors tropical weather systems and issues warnings as needed. With 122 regional weather centers, the National Weather Service can ensure that most of the United States is covered at any given time with observation equipment such as radiosondes, weather buoys, and satellites. Employees also conduct field observations and collect data about prevailing temperature, humidity, and wind speed from the ground.
Because the National Weather Service is a government agency, the services it provides are free. Citizens can listen to NOAA weather channels on the radio to get information about weather conditions, and they can also visit the National Weather Service's website, which has forecasts, warnings, and visual data such as satellite images. People can also participate in outreach and education programs which are designed to offer safety training for dealing with hazardous weather.