The agency first became a civilian enterprise in 1890, when it became part of the Department of Agriculture; it would later be moved to the Department of Commerce in 1940. The first Weather Bureau radiosonde was launched in Massachusetts in 1937, which went on to replace all routine aircraft observation within two years. The Bureau was renamed the National Weather Service in 1967, as part of the Environmental Science Services Administration, which became the National Oceanic and Atmospheric Administration (NOAA) three years later with the enactment of the National Environmental Policy Act.
The NWS issues a comprehensive package of forecast products to support a variety of users, including the general public. Although text forecasts have been the primary means of product dissemination, the NWS has been converting its forecast products to a digital, gridded format. Each of the 122 Weather Forecast Offices (WFOs) send their graphical forecasts to a national server to be compiled in the National Digital Forecast Database (NDFD). This is a collection of sensible weather elements such as: maximum and minimum temperature, humidity, cloud cover, probability of precipitation, amount of precipitation and wintry precipitation, weather type, and wind direction and speed. In addition to viewing () gridded weather data via the internet, more advanced users can decode the individual grids using a "GRIB2 decoder" which can output data as shapefiles, netCDF, GrADS, float files, and comma separated variable files. Specific points in the digital database can be accessed using an XML SOAP service (). These capabilities have greatly increased the audience of NDFD data. The NWS has received some criticism from commercial weather vendors for providing graphical forecast data free of charge. They argue that such tailored forecast information compete with their own products. However, a large majority of private weather firms quickly realized its potential benefits and have flourished by using the NDFD as a tool for composing their products.
The NWS supports the aviation community through the production of several specific forecast products. Each WFO has responsibility for the issuance of Terminal Aerodrome Forecasts (TAF) for one or more airports in their jurisdiction. TAFs are concise, coded 24-hour forecasts for a specific airport, issued every six hours with amendments as needed. As opposed to a public weather forecast, a TAF only addresses weather elements critical to aviation. These are: wind, visibility, weather, sky condition (clouds), and optional data such as wind shear. The following is an example of a TAF for Will Rogers World Airport in Oklahoma City:
KOKC 212350Z 220024 10006KT P6SM SCT040 BKN120
TEMPO 0001 VRB15G25KT 2SM +TSRA BKN040CB OVC070
FM0100 10007KT P6SM SCT040CB BKN060 BKN120
TEMPO 0105 2SM +TSRA BKN030CB OVC050
FM0500 07006KT 5SM SHRA BKN030CB OVC050
TEMPO 0508 3SM +TSRA OVC030CB
FM1200 03006KT P6SM -SHRA BKN025 OVC070
FM1600 05007KT P6SM BKN035 OVC100
21 NWS Center Weather Service Units (CWSU) are collocated with the Federal Aviation Administration (FAA) Air Route Traffic Control Centers (ARTCC). Their main responsibility is to provide up-to-the-minute weather information and briefings to the Traffic Management Units and control room supervisors. Special emphasis is given to weather conditions that would be hazardous to aviation or would impede the flow of air traffic in the National Airspace System. Beside scheduled and unscheduled briefings for decision-makers in the ARTCC and other FAA facilities, CWSU meteorologists also issue two unscheduled products. The Center Weather Advisory (CWA) is an aviation weather warning for thunderstorms, icing, turbulence, and low cloud ceilings and visibilities. The Meteorological Impact Statement (MIS) is a 2-12 hour forecast for weather conditions which are expected to impact ARTCC operations.
The local weather office also, under a prescribed set of criteria, will determine if a Fire Weather Watch or a Red Flag Warning needs to be issued. These products alert not only the public, but other agencies that conditions are creating the potential for extreme fire behavior.
On the national level, the NWS Storm Prediction Center issues fire weather analyses for days one and two. These include large-scale areas that may experience critical fire weather conditions including the occurrence of "dry thunderstorms." These are thunderstorms, usually occurring in the western U.S., that are not accompanied by any rain due to it evaporating before reaching the surface.
State and Federal forestry officials sometimes request a forecast from a WFO for a specific location called a "spot forecast." Spot forecasts are used to determine whether it will be safe to ignite a prescribed burn and how to situate crews during the controlling phase. Officials send in a request, usually during the early morning, containing the position coordinates of the proposed burn, the ignition time, and other pertinent information. The WFO composes a short-term fire weather forecast for the location and sends it back to the officials, usually within an hour of receiving the request.
The NWS assists officials at large wildfires or other disasters, including HAZMAT incidents, by providing on-ground support through Incident Meteorologists (IMET). IMETs are NWS forecasters specially trained to work with Incident Management Teams during severe wildfire outbreaks or other disasters requiring onsite weather support. IMETs travel quickly to the incident site and then assemble a mobile weather center capable of providing continuous meteorological support for the duration of the incident. The kit includes a cell phone, a laptop computer and communications equipment, used for gathering and displaying weather data such as satellite imagery or numerical forecast model output. Remote weather stations are also used to gather specific data for the point of interest. They often receive direct support from the local WFO during such crises. IMETS can be deployed anywhere a disaster strikes and must be capable of working long hours for weeks at a time in remote locations under rough conditions. There are approximately 60 to 70 IMETs nationally.
A significant portion of NWS forecasting is directed toward the general public. Because coded products are very difficult to understand by someone not familiar with the coding, most NWS public products are written using basic meteorological terminology in a sentence format. The main public forecasts products are:
NWS forecasts are available from their website. Previously, upon clicking a location on the map, the zone forecast for that county would appear. Now that the National Digital Forecast Database is operational, the internet forecasts have become "point-and-click," with the web server instantly composing a narrative text forecast for a particular point on the grid. This capability greatly reduces discontinuities in the forecast and takes full advantage of the detail put into the forecast by NWS meteorologists.
The NWS is the primary source for hydrologic watches, warnings, and advisories for the United States of America. Local NWS offices are responsible for issuing: Flood Watches, Flash Flood Watches, Flood Warnings, Flash Flood Warnings and Flood Advisories for their local County Warning Area. These products can and do emphasize different hydrologic issues depending on geographic area, land use, time of year, as well as other meteorological and non-meteorological factors. For example, during the early spring or late winter a Flood Warning can be issued for an ice jam that occurs on a river, while in the summer a Flood Warning will most likely be issued for excessive rainfall. For the official definition of all the NWS hydrology products, see the NWS glossary
In recent years the NWS has enhanced its dissemination of hydrologic information through the Advanced Hydrologic Prediction Service, more commonly referred to by the acronym (AHPS). AHPS allows anyone to view near real time observation and forecast data for rivers, lakes and streams. AHPS also enables the NWS to provide long-range probabilistic information which can be used for long-range planning decisions.
Daily river forecasts are issued by the 13 River Forecast Centers (RFC) using hydrologic models based on rainfall, soil characteristics, precipitation forecasts, and several other variables. Some RFCs, especially those in mountainous regions, also provide seasonal snow pack and peak flow forecasts. These forecasts are used by a wide range of users, including those in agriculture, hydroelectric dam operation, and water supply resources.
The NWS's mission to protect life and property and to enhance the national economy includes a suite of products for the water bodies adjacent to the U.S.. The marine forecasting program is aimed at promoting safe and efficient transportation, both commercial and recreational. NWS national centers or WFOs issue several marine products:
The National Hurricane Center (NHC) and the Central Pacific Hurricane Center (CPHC) are responsible for monitoring tropical weather in the Atlantic, and central and eastern Pacific Ocean. In addition to routine outlooks and discussions, they initiate advisories and discussions on individual tropical cyclones, as needed. If a tropical cyclone threatens the United States or its territories, individual WFOs begin issuing statements detailing the expected local effects. The following tropical weather products are issued by the NWS:
Additionally, Weather Forecast Offices issue daily and monthly climate reports for their area of responsibility. These generally include recorded highs, lows and other information. Since this data is not official until it has been quality controlled by NCDC, when these products are made available from Forecast Offices () they are considered to be unofficial and preliminary and cannot be used in a court of law.
METAR KNXX 121155Z 03018G29KT 1/4SM +TSSN FG VV002 M05/M07 A2957 RMK PK WND 01029/1143 SLP026
SNINCR 2/10 RCRNR T2 SET 6///// 7//// 4/010 T10561067 11022 21056 55001 PWINO PNO FZRANO
Getting more information on the atmosphere, more frequently, and from more locations is the key to improving forecasts and warnings. Due to the large installation and operating costs associated with ASOS, the stations are widely spaced. Before aviation weather observing began, the Cooperative Observer Program (COOP) was the only means for acquiring daily weather information. This network of approximately 11,000 mostly volunteer weather observers still flourishes today, providing much of the meteorological and climatological data to the country. The program which was established in 1890 under the Organic Act, currently has a twofold mission:
NWS forecasters need frequent, high-quality marine observations to examine conditions for forecast preparation and to verify their forecasts after they are produced. These observations are especially critical to the output of numerical weather models because large water bodies have a profound impact on the weather. Other users rely on the observations and forecasts for commercial and recreational activities. To help meet these needs, the NWS's National Data Buoy Center (NDBC) operates a network of about 90 buoys and 60 land-based coastal observing systems (C-MAN). All stations measure wind speed, direction, and gust; barometric pressure; and air temperature. In addition, all buoy stations, and some C-MAN stations, measure sea surface temperature and wave height and period. Conductivity and water current are measured at selected stations. All stations report hourly.
Supplemental weather observations are acquired through the United States Voluntary Observing Ship (VOS) program. It is organized for the purpose of obtaining weather and oceanographic observations from transiting ships. An international program under World Meteorological Organization (WMO) marine auspices, the VOS has forty-nine countries as participants. The United States program is the largest in the world, with nearly 1,000 vessels. Observations are taken by deck officers, coded in a special format known as the "ships synoptic code", and transmitted in realtime to the NWS. They are then distributed on national and international circuits for use by meteorologists in weather forecasting, by oceanographers, ship routing services, fishermen, and many others. The observations are then forwarded for use by the National Climatic Data Center (NCDC) in Asheville, North Carolina.
Upper air weather data is essential for weather forecasting and research. The NWS operates 92 radiosonde locations in North America and 10 sites in the Caribbean. A small, expendable instrument package is suspended below a 2 meter (6 ft) wide balloon filled with hydrogen or helium, then released daily at or shortly after 11 UTC and 23 UTC. As the radiosonde rises at about 300 meters/minute (1,000 ft/min), sensors on the radiosonde measure profiles of pressure, temperature, and relative humidity. These sensors are linked to a battery powered radio transmitter that sends the sensor measurements to a ground receiver. By tracking the position of the radiosonde in flight, information on wind speed and direction aloft is also obtained. The flight can last longer than two hours, and during this time the radiosonde can ascend above 35 km (115,000 ft) and drift more than 200 km (125 mi) from the release point. When the balloon has expanded beyond its elastic limit and bursts (about 6 m or 20 ft in diameter), a small parachute slows the descent of the radiosonde, minimizing the danger to lives and property.
Data obtained during the flights is coded and disseminated, at which point it can be plotted on a Skew-T or Stuve diagram for analysis.
In recent years, the National Weather Service has begun incorporating data from AMDAR in its numerical models (however, the raw data is not available to the public).
The National Weather Service has developed a multi-tier concept for forecasting or alerting the public to all types of hazardous weather. These are:
Outlook - A hazardous weather outlook is issued daily addressing potentially hazardous weather or hydrologic events that may occur in the next seven days. The outlook will include information about potential severe thunderstorms, heavy rain or flooding, winter weather, extremes of heat or cold, etc. It is intended to provide information to those who need considerable lead time to prepare for the event. Other outlooks are issued on an event-driven basis, such as the Flood Potential Outlook and Severe Weather Outlook.
Watch - A watch is used when the risk of a hazardous weather or hydrologic event has increased significantly, but its occurrence, location or timing is still uncertain. It is intended to provide enough lead time so those who need to set their plans in motion can do so. A watch means that hazardous weather is possible, but not imminent. People should have a plan of action in case a storm threatens and they should listen for later information and possible warnings especially when planning travel or outdoor activities.
Warning - A warning is issued when a hazardous weather or hydrologic event is occurring, imminent or likely. A warning means weather conditions pose a threat to life or property. People in the path of the storm need to take protective action.
Advisory - An advisory is issued when a hazardous weather or hydrologic event is occurring, imminent or likely. Advisories are for less serious conditions than warnings, that cause significant inconvenience and if caution is not exercised, could lead to situations that may threaten life or property.
Special Weather Statement - A special weather statement is issued when something rare or unusual is occurring. These are usually triggered by sudden changes in meteorological conditions. The statements are to be taken as warnings for residents of a specific area. The warning generally states that an area might be at risk for a slight weather danger. Not all weather statements are warnings, though. Other times, statements describe informative facts about a weather system; such as local snowfall.
NOAA Weather Radio All-Hazards (NWR), sometimes called Weatheradio (though this is actually a trademark of receiver manufacturer Tandy), is a special radio system that transmits weather warnings and forecasts 24 hours a day across most of the United States. The system, owned and operated by the NWS, consists of more than 900 transmitters, covering all 50 states, adjacent coastal waters, Puerto Rico, the U.S. Virgin Islands, and the U.S. Pacific Territories. NWR requires a special radio receiver or scanner capable of picking up the signal. It is broadcast on seven frequencies centered around 162 MHz in the VHF frequency band. In recent years, national emergency response agencies such as FEMA and the Department of Homeland Security have begun to take advantage of NWR's ability to efficiently reach a large portion of the population. The system is now used to broadcast civil and natural emergency information in addition to that relating to weather.
NOAA Weather Wire Service (NWWS) is a satellite data collection and dissemination system operated by the National Weather Service. Its purpose is to provide state and federal government, commercial users, media, and private citizens with timely delivery of meteorological, hydrological, climatological, and geophysical information. All products in the NWWS datastream are prioritized, with weather and hydrologic warnings receiving the highest priority (watches are next in priority). NWWS delivers severe weather and storm warnings to users in 10 seconds or less from the time they are issued, making it the fastest delivery system available. Products are broadcast to users via the AMC-4 satellite.
EMWIN is the Emergency Managers Weather Information Network, a system designed to provide the emergency management community with access to a set of NWS warnings, watches, forecasts, and other products at no recurring cost. Its can receive data via radio, internet, or a dedicated satellite dish, depending on the needs and capabilities of the user.
The NOAAPORT broadcast system provides a one-way broadcast communication of NOAA environmental data and information in near real time to NOAA and external users. This broadcast service is implemented by a commercial provider of satellite communications utilizing C-band.
The Weather.gov website is a data rich website operated by NWS that serves as a portal to hundreds of thousands of webpages and more than 300 different NWS websites. From the homepage, it is possible to enter a city and state to get a local forecast page, view a rapidly updated map of active watch and warnings, and select areas related to graphical forecasts, national maps, radar displays, rivers, air quality, satellite images and climate. Also offered are xml data feeds of active watch and warnings, ASOS observations and digital forecasts for 5x5 kilometer grids.
The Interactive Weather Information Network (IWIN) is an internet site operated by the NWS that has been superseded by the weather.gov and has recently been proposed for termination.
Since 1983, the NWS has provided external user access to U.S. Government obtained or derived weather information through a collection of data communication line services called the Family of Services (FOS). FOS is accessible via dedicated telecommunications access lines in the Washington, D.C., area. All FOS data services are driven by the NWS Telecommunication Gateway computer systems located at NWS headquarters in Silver Spring, MD. Users may obtain any of the individual services from NWS for a one-time connection charge and an annual user fee.
Every NWS office operates its own web page with access to current products and other information specific to the local area.
NWS meteorologists use an advanced information processing, display, and telecommunications system called AWIPS to complete their work. These workstations allow them to easily view a multitude of weather and hydrologic information, as well as compose and disseminate products.
While generally respected as one of the premier weather organizations in the United States, the National Weather Service has been perceived by some, particularly libertarians and commercial weather services such as AccuWeather, as competing unfairly with the private sector. In 2005, Senator Rick Santorum (R-PA) introduced the National Weather Service Duties Act of 2005, a bill intended to limit the NWS's ability to provide data that could be given just as easily by commercial outlets, but at a cost. The bill was widely criticized by users of the NWS's services. The bill died in committee during the 2005 session.