History
The NWS, formerly known as the Weather Bureau, was founded on February 9, 1870 through a joint congressional resolution signed by President Ulysses S. Grant. The mission of the NWS was "to provide for taking meteorological observations at the military stations in the interior of the continent and at other points in the States and Territories...and for giving notice on the northern (Great) Lakes and on the seacoast by magnetic telegraph and marine signals, of the approach and force of storms." The agency was placed under the Secretary of War because "military discipline would probably secure the greatest promptness, regularity, and accuracy in the required observations." Within the Department of War, it was assigned to the U.S. Army Signal Corps under Brigadier General Albert J. Myer. General Meyer gave the National Weather Service its first name: The Division of Telegrams and Reports for the Benefit of Commerce.
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.
Aviation
Meteorologists preparing a forecast, early 20th century.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 Aviation Weather Center (AWC), located in Kansas City, MO, is a central aviation-support facility operated by the National Weather Service. The AWC issues two primary products:
AIRMET (Airmen's Meteorological Information): Information on icing, turbulence, mountain obscuration, low-level wind shear, IMC conditions, and strong surface winds.
SIGMETs (Significant Meteorological Information)
Convective: Issued for an area of thunderstorms affecting an area of 3,000 square miles (7,800 km2) or greater, a line of thunderstorms at least 60 nmi (110 km) long, and/or severe or embedded thunderstorms affecting any area that are expected to last 30 minutes or longer.
Non-convective: Issued for severe or greater turbulence over a 3,000 square miles (7,800 km2) area, severe or greater icing over a 3,000 square miles (7,800 km2), or IMC conditions over a 3,000 square miles (7,800 km2) area due to dust, sand, or volcanic ash.
Fire weather
Catering to national, regional and local land management agencies such as the US Forest Service, the NWS issues a complete Fire Weather Forecast twice daily, with updates as needed. The forecast contains weather information relevant to fire control and smoke management for the next 36-48 hours. The appropriate crews use this information to plan for staffing and equipment levels, the ability to do prescribed burns, and assess the daily fire danger. Once per day, NWS meteorologists issue a coded fire weather forecast for specific USFS observation sites that are then input into the National Fire Danger Rating System (NFDRS). This computer model outputs the daily fire danger that is then conveyed to the public in one of four ratings: low, moderate, high, extreme.
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.
NWS IMET taking observations in the fieldState 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.
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