National Weather Service
The National Weather Service
(NWS) is an agency of the United States federal government that is tasked with
providing weather forecasts, warnings of hazardous weather, and other
weather-related products to organizations and the public for the purposes of
protection, safety, and general information. It is a part of the National
Oceanic and Atmospheric Administration (NOAA) branch of the Department of
Commerce, and is headquartered in Silver Spring, Maryland, within the
Washington metropolitan area. The agency was known as the United States Weather
Bureau from 1890 until it adopted its current name in 1970. The NWS performs
its primary task through a collection of national and regional centers, and 122
local Weather Forecast Offices (WFOs). As the NWS is an agency of the U.S.
federal government, most of its products are in the public domain and available
free of charge.
History: In 1870, the
Weather Bureau of the United States was established through a joint resolution
of Congress signed by President Ulysses S. Grant with a mission 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 as Congress felt "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 Service under Brigadier General Albert J. Myer. General
Myer gave the National Weather Service its first name: The Division of
Telegrams and Reports for the Benefit of Commerce.
Cleveland Abbe – who began
developing probabilistic forecasts using daily weather data sent by the
Cincinnati Chamber of Commerce and Western Union, which he convinced to back
the collection of such information in 1869 – was appointed as the Bureau's
first chief meteorologist. In his earlier role as the civilian assistant to the
chief of the Signal Service, Abbe urged the Department of War to research
weather conditions to provide a scientific basis behind the forecasts; he would
continue to urge the study of meteorology as a science after becoming Weather
Bureau chief. While a debate went on between the Signal Service and Congress
over whether the forecasting of weather conditions should be handled by
civilian agencies or the Signal Service's existing forecast office, a
Congressional committee was formed to oversee the matter, recommending that the
office's operations be transferred to the Department of War following a
two-year investigation.
The agency first became a
civilian enterprise in 1890, when it became part of the Department of
Agriculture. Under the oversight of that branch, the Bureau began issuing flood
warnings and fire weather forecasts, and issued the first daily national
surface weather maps; it also established a network to distribute warnings for
tropical cyclones as well as a data exchange service that relayed European
weather analysis to the Bureau and vice versa. The first Weather Bureau
radiosonde was launched in Massachusetts in 1937, which prompted a switch from
routine aircraft observation to radiosondes within two years. The Bureau
prohibited the word "tornado" from being used in any of its weather
products out of concern for inciting panic (a move contradicted in its
intentions by the high death tolls in past tornado outbreaks due to the lack of
advanced warning) until 1938, when it began disseminating tornado warnings
exclusively to emergency management personnel. The Bureau would later be moved
to the Department of Commerce in 1940. On July 12, 1950, Bureau chief Francis W.
Reichelderfer officially lifted the agency's ban on public tornado alerts in a
Circular Letter, noting to all first order stations that "Weather Bureau
employees should avoid statements that can be interpreted as a negation of the
Bureau's willingness or ability to make tornado forecasts", and that a
"good probability of verification" exist when issuing such forecasts
due to the difficulty in accurately predicting tornadic activity. However, it
would not be until it faced criticism for continuing to refuse to provide
public tornado warnings and preventing the release of the USAF Severe Weather
Warning Center's tornado forecasts (pioneered in 1948 by Air Force Capt. Robert
C. Miller and Major Ernest Fawbush) beyond military personnel that the Bureau
issued its first experimental public tornado forecasts in March 1952. In 1957, the Bureau began using radars for
short-term forecasting of local storms and hydrological events, using modified
versions of those used by Navy aircraft to create the WSR-57 (Weather
Surveillance Radar, 1957), with a network of WSR systems being deployed
nationwide through the early 1960s; some of the radars were upgraded to WSR-74
models beginning in 1974.
The Weather Bureau became part of
the Environmental Science Services Administration when that agency was formed
in August 1966. The Environmental Science Services Administration was renamed
the National Oceanic and Atmospheric Administration (NOAA) on October 1, 1970,
with the enactment of the National Environmental Policy Act. At this time, the
Weather Bureau became the National Weather Service. NEXRAD (Next Generation
Radar), a system of Doppler radars deployed to improve the detection and
warning time of severe local storms, replaced the WSR-57 and WSR-74 systems
between 1988 and 1997.
Forecast sub-organizations: The
NWS, through a variety of sub-organizations, issues different forecasts to
users, including the general public. Although, throughout history, text
forecasts have been the means of product dissemination, the NWS has been using
more forecast products of a digital, gridded, image or other modern 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). The NDFD is a collection of common weather observations used by
organizations and the public, including precipitation amount, temperature, and
cloud cover among other parameters. In addition to viewing gridded weather data
via the internet, users can download and use 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.
Weather Forecast Offices: The
National Weather Service uses local branches, 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 Continental 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 and tornado warnings, flood, 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.
Aviation: The NWS supports
the aviation community through the production of several forecasts. Each area's
WFO has responsibility for the issuance of Terminal Aerodrome Forecasts (TAFs)
for airports in their jurisdiction. TAFs are concise, coded 24-hour forecasts
(30-hour forecasts for certain airports) for a specific airport, which are
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 include wind, visibility, cloud cover and wind shear. Twenty-one 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 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
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. The Aviation Weather Center (AWC), located in Kansas City,
Missouri, is a central aviation support facility operated by the National
Weather Service.
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:
The Weather Prediction Center in College Park, Maryland provides guidance for
future precipitation amounts and areas where excessive rainfall is likely,[28]
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).
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, and central and
eastern Pacific Oceans. 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.
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