Editing National Weather Service (section)

== Field offices ==

===Weather Forecast Offices===
{{see also|List of National Weather Service Weather Forecast Offices}}
[[File:NWS Weather Forecast Offices.svg|thumb|center|Map of NWS Weather Forecast Offices. Colors indicate area of responsibility, letters indicate each office's call sign. Alaska, Pacific and Puerto Rico offices are only indicated with call sign letters in the corners.|upright=3]]

The National Weather Service operates 122 local offices, known as Weather Forecast Offices (WFOs), to issue products specific to those areas. Each WFO maintains a specific area of responsibility spanning multiple counties, parishes or other jurisdictions within the United States – which, in some areas, cover multiple states – or individual possessions; the local offices handle responsibility of composing and disseminating forecasts and weather alerts to areas within their region of service. Some of the products that are only issued by the WFOs are [[severe thunderstorm warning|severe thunderstorm]] and [[Tornado Warning|tornado]] warnings, flood, [[flash flood warning|flash flood]], and winter weather watches and warnings, some aviation products, and local forecast grids. The forecasts issued by a WFO are available on their individual pages within the Weather.gov website, which can be accessed through either forecast landing pages (which identify the office that disseminates the weather data) or via the alert map featured on the main page of the National Weather Service website.
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=== River Forecast Centers ===
Daily river forecasts are issued by the thirteen River Forecast Centers (RFCs) using hydrologic models based on rainfall, soil characteristics, precipitation forecasts, and several other variables. The first such center was founded on September 23, 1946.<ref name="ERHhist">{{cite web |title=History of OHRFC |url=http://www.erh.noaa.gov/ohrfc/history.html |url-status=dead |archive-url=https://web.archive.org/web/20030124181255/http://www.erh.noaa.gov/ohrfc/history.html |archive-date=January 24, 2003 |access-date=February 26, 2012 |publisher=National Weather Service}}</ref> 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]], [[hydroelectricity|hydroelectric dam]] operation, and [[Water resources|water supply]] resources.

=== Center Weather Service Units ===
Twenty-one NWS Center Weather Service Units (CWSUs) are collocated with the [[Federal Aviation Administration|Federal Aviation Administration (FAA)]] [[Area Control Center|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 could be hazardous to aviation or impede the flow of air traffic in the [[National Airspace System]]. Besides 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 [[ceiling (cloud)|cloud ceilings]] and visibilities. The Meteorological Impact Statement (MIS) is a two- to 12-hour forecast that outlines weather conditions expected to impact ARTCC operations.<ref name="awccwsus">{{cite web |title=AWC – Center Weather Service Unit Products (CWA, MIS) |url=http://aviationweather.gov/products/cwsu/ |url-status=dead |archive-url=https://web.archive.org/web/20121226092742/http://aviationweather.gov/products/cwsu |archive-date=December 26, 2012 |access-date=December 11, 2012 |website=Aviation Weather Center |publisher=National Weather Service}}</ref>

===National Centers for Environmental Prediction===
{{main|National Centers for Environmental Prediction}}

====Aviation Weather Center====
[[Image:Wea01302 - Flickr - NOAA Photo Library.jpg|thumb|Meteorologists preparing a forecast, early 20th century.]]

The Aviation Weather Center (AWC), located in [[Kansas City, Missouri]], is a central aviation support facility operated by the National Weather Service, which issues two primary products:
* [[AIRMET]] (Airmen's Meteorological Information) – Information on [[Icing conditions|icing]], [[turbulence]], mountain obscuration, low-level wind shear, [[instrument meteorological conditions]], and strong surface winds.
* [[SIGMET]]s (Significant Meteorological Information) – Issued for significant weather that may affect an airport of flight path in an area:
** Convective – Issued for an area of thunderstorms affecting an area of {{convert|3000|sqmi|km2}} or greater, a line of thunderstorms at least {{convert|60|nmi|km|abbr=on}} long, or severe or embedded thunderstorms affecting any area that are expected to last 30 minutes or longer.
** Non-convective – Issued for severe turbulence over a {{convert|3000|sqmi|km2}} area, severe icing over a {{convert|3000|sqmi|km2}}, or instrument meteorological conditions over a {{convert|3000|sqmi|km2}} area due to dust, sand, or volcanic ash.

====Storm Prediction Center====
{{main|Storm Prediction Center}}

The Storm Prediction Center (SPC) in [[Norman, Oklahoma]] issues severe thunderstorm and tornado watches in cooperation with local WFOs which are responsible for delineating jurisdictions affected by the issued watch, and SPC also issues mesoscale discussions focused upon possible convective activity. SPC compiles reports of severe hail, wind, or tornadoes issued by local WFOs each day when thunderstorms producing such phenomena occur in a given area, and formats the data into text and graphical products. It also provides forecasts on convective activity through day eight of the forecast period (most prominently, the threat of severe thunderstorms, the risk of which is assessed through a tiered system conveyed among six categories – general thunderstorms, marginal, slight, enhanced, moderate, or high – based mainly on the expected number of storm reports and regional coverage of thunderstorm activity over a given forecast day), and is responsible for issuing fire weather outlooks, which support local WFOs in the determination of the need for Red Flag Warnings.

====Weather Prediction Center====
{{main|Weather Prediction Center}}

The [[Weather Prediction Center]] in [[College Park, Maryland]] provides guidance for future precipitation amounts and areas where excessive rainfall is likely,<ref name="AboutHPC">{{cite web|title=About the HPC|url=http://www.wpc.ncep.noaa.gov/html/about2.shtml|website=[[Hydrometeorological Prediction Center]] |access-date=September 3, 2008}}</ref> while 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, as well as the official rainfall forecast for areas within their warning area of responsibility. 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).

[[File:2008-06-14 NOAA flooding overview.png|thumb|National AHPS map.]]

In recent years, the NWS has enhanced its dissemination of hydrologic information through the Advanced Hydrologic Prediction Service (AHPS).<ref name="AHPShome">{{cite web|title=About AHPS|url=http://www.weather.gov/ahps/about/about.php |publisher=National Weather Service|access-date=December 19, 2008}}</ref> The AHPS allows anyone to view near real-time observation and forecast data for rivers, lakes and streams. The service also enables the NWS to provide long-range probabilistic information which can be used for long-range planning decisions.

====Ocean Prediction Center====
[[File:NWSmarinezones.gif|thumb|The National Weather Service areas of marine weather forecasting responsibility.]]
{{main|Ocean Prediction Center}}

The National Weather Service [[Ocean Prediction Center]] (OPC) in [[College Park, Maryland]]<ref name="OPChome">{{cite web|title=Ocean Prediction Center|url=http://www.opc.ncep.noaa.gov/|website=[[National Centers for Environmental Prediction]]|publisher=National Weather Service|access-date=December 15, 2012|archive-url=https://web.archive.org/web/20071006170925/http://www.opc.ncep.noaa.gov/|archive-date=October 6, 2007|url-status=dead}}</ref> issues [[marine weather forecasting|marine products]] for areas that are within the national waters of the United States. NWS national centers or Weather Forecast Offices 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 five; it also addresses expected wave heights.
* Offshore Waters Forecast (OFF) – a text product issued by the OPC that provides forecast and warning information to mariners who travel on the oceanic waters adjacent to the U.S. coastal waters through day five. 
* NAVTEX forecast – a text forecast issued by the OPC (combining data from the Coastal Waters and Offshore Waters Forecasts) designed to accommodate broadcast restrictions of [[United States Coast Guard|U.S. Coast Guard]] [[NAVTEX]] transmitters. 
* 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.

====National Hurricane Center====
{{main|National Hurricane Center}}

The [[National Hurricane Center]] (NHC) and the [[Central Pacific Hurricane Center]] (CPHC), respectively based in [[Miami, Florida]] and [[Honolulu, Hawaii]], are responsible for monitoring tropical weather in the [[Atlantic Ocean|Atlantic]], and central and eastern [[Pacific Ocean]]s. In addition to releasing routine outlooks and discussions, the guidance center initiates 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 effects within their local area of responsibility. The NHC and CPHC issue products including tropical cyclone advisories, forecasts, and formation predictions, and warnings for the areas in the Atlantic and parts of the Pacific.

[[File:NOAA-CPC-seasonal-temp-outlook.gif|right|125px|thumb|Sample CPC 3.5-month temperature outlook.]]

====Climate Prediction Center====
{{main|Climate Prediction Center}}

The [[Climate Prediction Center]] (CPC) in [[College Park, Maryland]] 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 the products issued by the center cover the [[Contiguous United States|Contiguous U.S.]] and [[Alaska]].

Additionally, Weather Forecast Offices issue daily and monthly climate reports for official climate stations within their area of responsibility. These generally include recorded highs, lows and other information (including historical temperature extremes, fifty-year temperature and precipitation averages, and [[degree day]]s). This information is considered preliminary until certified by the [[National Climatic Data Center]].

==== Space Weather Prediction Center ====
{{main|Space Weather Prediction Center}}
The [[Space Weather Prediction Center]] (SWPC), located in Boulder, Colorado, is responsible for monitoring and issuing forecasts, alerts, and warnings related to solar activity that may affect terrestrial activities. In particular, SWPC is concerned with how events such as [[Coronal mass ejection|coronal mass ejections]] (CMEs), [[Geomagnetic storm|geomagnetic storms]], [[Solar flare|solar flares]], and other phenomena can impact [[electric power transmission]], [[Global Positioning System|GPS]] systems, [[High frequency|HF]] radio and [[satellite]] communications, as well as other potential impacts.

SWPC also issues [[aurora]] forecasts for both the [[Northern Hemisphere]] and [[Southern Hemisphere]].