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The National Weather Service (NWS) is one of the six scientific agencies that make up the National Oceanic and Atmospheric Administration (NOAA) of the United States government. It is tasked with providing "weather, hydrologic, and climate forecasts and warnings for the United States, its territories, adjacent waters and ocean areas, for the protection of life and property and the enhancement of the national economy." This is done through a collection of national and regional centers, and more than 122 local weather forecast offices (WFOs). Since the NWS is a government agency, most of its products are available free of charge.

History

The NWS was founded on February 9th, 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."*

Forecasting

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, 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 ([http://www.weather.gov/xml/). 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

The NWS supports the general aviation community through several specific forecasts. The primary aviation product is the Terminal Aerodrome Forecast (TAF), a concise, coded 24-hour forecast for a specific airport. 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

Transcribed Weather Enroute Broadcasts (TWEBs) are composed by some WFOs. These contain similar information to a TAF but are for a 50 mile wide corridor between two or three frequently connected airports. Some TWEB routes are accompanied by a short weather synopsis. This is a sample TWEB for the route Wilmington, NC - New Bern, NC - Norfolk, VA:

041 TWEB 242008 KILM-KEWN-KORF. ALL HGTS AGL EXC TOPS. KILM-KEWN P6SM SCT025 BKN050 WDLY SCT 5SM -SHRA BKN025...22Z P6SM SCT050 SCT-BKN120...02Z P6SM SCT150. KEWN-KORF P6SM SCT030 SCT-BKN080 LCL BKN030...22Z P6SM SCT030...01Z P6SM SKC.=

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. CWSU meteorologists also issue two unscheduled products. The Center Weather Advisory (CWA) is an aviation weather warning for thunderstorms, icing, turbulence, and low ceilings and visibilities. The Meteorological Impact Statement (MIS) is a 2-12 hour forecast for weather conditions which are expected to impact ARTCC operations.

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.

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 , as it evaporates in the very dry air before reaching the ground. State and Federal forestry officials sometimes request a forecast from a WFO for a specific location called a "spot forecast." Spot forecasts are mostly used to plan for a controlled burn, to determine whether it will be safe to ignite it 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 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 a two-way portable satellite dish 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.

Public

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:

  • Zone Forecast Product (ZFP) - text product issued by all WFOs to explicitly state expected weather conditions within each zone in their area of forecast responsibility through day seven.
  • Surf Zone Forecast (SRF) - a text forecast for local beaches issued by coastal WFOs, including coastal hazard information such as that pertaining to rip currents. These products are issued year-round at the Los Angeles, San Diego, and New York City offices, and seasonally at most other coastal offices.
  • Short Term Forecast (NOW) - a localized, event-driven product used to provide the public with detailed weather information during significant and/or fast-changing hydrometeorological conditions during the next six hours.
  • Area Forecast Matrices (AFM) - displays various weather parameters at 3, 6 and 12 hour intervals for areas specified in the current ZFP.
  • Point Forecast Matrices (PFM) - displays various weather parameters at 3, 6 and 12 hour intervals for significant cities in the WFO area of responsibility.
  • Tabular State Forecast Product (SFT) - general seven-day public forecast of hydrometeorological conditions at specific locations over a WFO's area of responsibility.
  • Area Forecast Discussion (AFD) - a semi-technical product primarily for explaining the scientific rationale behind a forecast and to summarize current watches/warnings/advisories in effect.

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.

Hydrologic

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.

Marine

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:

  • Coastal Waters Forecast (CWF) - a text product issued by all coastal WFOs to explicitly state expected weather conditions within their marine forecast area of responsibility through day 5. Also addresses expect wave heights.
  • Offshore Waters Forecast (OFF) - a text product that provides forecast and warning information to mariners who travel on the oceanic waters adjacent to the U.S. coastal waters through day 5. Issued by the Ocean Prediction Center (OPC).
  • NAVTEX forecast - a text forecast issued by OPC designed to accommodate broadcast restrictions of the U.S. Coast Guard NAVTEX transmitters. The product is a combination of the CWF and OFF.
  • High Seas Forecast (HSF) - routine text product issued every six hours by OPC to provide warning and forecast information to mariners who travel on the oceanic waters.

Tropical

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:

  • Routine Products
    • Tropical Weather Outlook (TWO)
      • Atlantic basin
      • Pacific basin
    • Tropical Weather Discussion (TWD)
      • Atlantic basin
      • Pacific basin
    • Tropical Weather Summary (TWS)
    • Satellite Interpretation Message (SIM)
  • Active Tropical Cyclone Products
    • Tropical/Subtropical Cyclone Public Advisory (TCP)
    • Tropical/Subtropical Cyclone Discussion (TCD)
    • Tropical Cyclone Forecast/Advisory (TCM)
    • Strike Probabilities of Tropical Cyclone Conditions (SPF)
  • Local WFO Products
    • Hurricane Local Statement (HLS)
    • Inland Tropical Storm/Hurricane Watches or Warnings (NPW)
    • Post-Tropical Cyclone Reports (PSH)

Climate

The Climate Prediction Center (CPC) is responsible for all of the NWS's climate-related forecasts. Their mission is to "serve the public by assessing and forecasting the impacts of short-term climate variability, emphasizing enhanced risks of weather-related extreme events, for use in mitigating losses and maximizing economic gains." Their products cover time scales from a week to seasons, extending into the future as far as technically feasible, and cover the land, the ocean, and the atmosphere, extending into the stratosphere. Most of their products cover the Contiguous U.S. and Alaska. Here is a list of the main CPC products:

  • 3-Month Temperature and Precipitation
    • Outlooks
    • Discussions
  • 1-Month Temperature and Precipitation
    • Outlooks
    • Discussions
  • 6 to 10-Day and 8 to 14-Day Products
    • Temperature and Precipitation Anomaly
    • Excessive Heat Outlook
    • Maximum Heat Index Prediction
  • 3-Month Probability of Exceedence
    • Temperature
    • Precipitation
    • Heating and Cooling Degree Days
  • Hurricane Season Outlook
    • Atlantic basin
    • Pacific basin
  • U.S. Drought
    • Outlook
    • Discussion

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.

Data Acquisition

Surface Observations

The Automated Surface Observing System (ASOS) is a joint effort of the National Weather Service (NWS), the Federal Aviation Administration (FAA), and the Department of Defense (DOD). The ASOS serves as the nation's primary surface weather observing network. It is designed to support weather forecast activities and aviation operations and, at the same time, support the needs of the meteorological, hydrological, and climatological research communities. ASOS was especially designed for the safety of the aviation community, therefore the sites are almost always located near airport runways. The system transmits routine hourly observations along with special observations when conditions exceed preselected weather element thresholds (e.g. the visibility decreases to less than 3 miles). The basic weather elements observed are: sky condition, visibility, present weather, obstructions to vision, pressure, temperature, dewpoint, wind direction and speed, precipitation accumulation, and selected significant remarks. The coded observations are issued as METARs and look similar to this: 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 two-fold mission:

  • Provide observational meteorological data, usually consisting of daily maximum and minimum temperatures, snowfall, and 24-hour precipitation totals, required to define the climate of the United States and to help measure long-term climate changes.
  • Provide observational meteorological data in near real-time to support forecast, warning and other public service programs of the NWS.

Marine Observations

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 Observations

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 00 UTC and 12 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.

Event-driven Products

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.

A detailed list defining NWS watches, warnings and advisories can be found on the Severe Weather Terminology page.

Product Dissemination

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 GE-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. A move is underway in the US Congress to severely limit these websites and other free access to NWS products, spearheaded by Senator Rick Santorum, whose Pennsylvania constituency includes major commercial weather provider Accuweather.

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.

Technology

The WSR-88D Doppler radar system, also called NEXRAD, was developed by the NWS during the mid 1980s and fully deployed by the early 1990s. There are 158 Doppler radar sites in the United States and selected overseas locations. This technology, because of its high resolution and ability to detect intra-cloud motions, is now the cornerstone of NWS severe weather warning operations.

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.

Organization

Controversy

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. The bill was widely criticized by users of the NWS's services; it was also noted that AccuWeather president Joel Myers was a Santorum campaign contributor. The bill did not become law in the 2005 session.

References

Internal Links

Other national weather services:

External links

National Weather Service | Meteorological institutions and stations

National Weather Service | National Weather Service

 

This article is licensed under the GNU Free Documentation License. It uses material from the "National Weather Service".

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