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Weather forecasting is the application of science and technology
to predict the conditions of the
atmosphere for a given location and time. People have attempted to predict the weather informally for
millennia
A millennium (plural millennia or millenniums) is a period of one thousand years, sometimes called a kiloannum (ka), or kiloyear (ky). Normally, the word is used specifically for periods of a thousand years that begin at the starting point (ini ...
and formally since the 19th century. Weather forecasts are made by collecting quantitative data about the current state of the atmosphere, land, and ocean and using
meteorology
Meteorology is a branch of the atmospheric sciences (which include atmospheric chemistry and physics) with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant progress in meteorology did no ...
to project how the atmosphere will change at a given place.
Once calculated manually based mainly upon changes in
barometric pressure, current weather conditions, and sky condition or cloud cover, weather forecasting now relies on
computer-based models that take many atmospheric factors into account. Human input is still required to pick the best possible forecast model to base the forecast upon, which involves pattern recognition skills,
teleconnections, knowledge of model performance, and knowledge of model biases. The inaccuracy of forecasting is due to the
chaotic nature of the atmosphere, the massive computational power required to solve the equations that describe the atmosphere, the land, and the ocean, the error involved in measuring the initial conditions, and an incomplete understanding of atmospheric and related processes. Hence, forecasts become less accurate as the difference between current time and the time for which the forecast is being made (the ''range'' of the forecast) increases. The use of ensembles and model consensus help narrow the error and provide confidence level in the forecast.
There is a vast variety of end uses to weather forecasts.
Weather warnings are important forecasts because they are used to protect life and property. Forecasts based on temperature and
precipitation
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...
are important to agriculture, and therefore to traders within commodity markets. Temperature forecasts are used by utility companies to estimate demand over coming days. On an everyday basis, many use weather forecasts to determine what to wear on a given day. Since outdoor activities are severely curtailed by heavy rain, snow and
wind chill, forecasts can be used to plan activities around these events, and to plan ahead and survive them.
Weather forecasting is a part of the economy, for example, in 2009, the US spent approximately $5.1 billion on weather forecasting, producing benefits estimated at six times as much.
History
Ancient forecasting
For millennia, people have tried to forecast the weather. In 650 BC, the
Babylonians predicted the weather from cloud patterns as well as
astrology
Astrology is a range of divinatory practices, recognized as pseudoscientific since the 18th century, that claim to discern information about human affairs and terrestrial events by studying the apparent positions of celestial objects. Di ...
. In about 350 BC,
Aristotle
Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of ph ...
described weather patterns in ''
Meteorologica''. Later,
Theophrastus
Theophrastus (; grc-gre, Θεόφραστος ; c. 371c. 287 BC), a Greek philosopher and the successor to Aristotle in the Peripatetic school. He was a native of Eresos in Lesbos.Gavin Hardy and Laurence Totelin, ''Ancient Botany'', Routle ...
compiled a book on weather forecasting, called the ''Book of Signs''. Chinese weather prediction lore extends at least as far back as 300 BC, which was also around the same time ancient
Indian astronomers developed weather-prediction methods. In
New Testament
The New Testament grc, Ἡ Καινὴ Διαθήκη, transl. ; la, Novum Testamentum. (NT) is the second division of the Christian biblical canon. It discusses the teachings and person of Jesus, as well as events in first-century Chri ...
times, Jesus himself referred to deciphering and understanding local weather patterns, by saying, "When evening comes, you say, 'It will be fair weather, for the sky is red', and in the morning, 'Today it will be stormy, for the sky is red and overcast.' You know how to interpret the appearance of the sky, but you cannot interpret the signs of the times."
In 904 AD,
Ibn Wahshiyya
( ar, ابن وحشية), died , was a Nabataean (Aramaic-speaking, rural Iraqi) agriculturalist, toxicologist, and alchemist born in Qussīn, near Kufa in Iraq. He is the author of the '' Nabataean Agriculture'' (), an influential Arabic work ...
's ''
Nabatean Agriculture
''The Nabataean Agriculture'' (), also written ''The Nabatean Agriculture'', is a 10th-century text on agronomy by Ibn Wahshiyya (died ), from Qussīn in present-day Iraq. It contains information on plants and agriculture, as well as on magic ...
'', translated into Arabic from an earlier
Aramaic
The Aramaic languages, short Aramaic ( syc, ܐܪܡܝܐ, Arāmāyā; oar, 𐤀𐤓𐤌𐤉𐤀; arc, 𐡀𐡓𐡌𐡉𐡀; tmr, אֲרָמִית), are a language family containing many varieties (languages and dialects) that originated in ...
work, discussed the weather forecasting of atmospheric changes and signs from the planetary astral alterations; signs of rain based on observation of the
lunar phases; and weather forecasts based on the movement of winds.
Ancient weather forecasting methods usually relied on observed patterns of events, also termed pattern recognition. For example, it was observed that if the sunset was particularly red, the following day often brought fair weather. This experience accumulated over the generations to produce
weather lore
Weather lore is the body of informal folklore related to the prediction of the weather and its greater meaning.
Much like regular folklore, weather lore is passed down through speech and writing from normal people without the use of external me ...
. However, not all of these predictions prove reliable, and many of them have since been found not to stand up to rigorous statistical testing.
Modern methods
It was not until the invention of the
electric telegraph
Electrical telegraphs were point-to-point text messaging systems, primarily used from the 1840s until the late 20th century. It was the first electrical telecommunications system and the most widely used of a number of early messaging systems ...
in 1835 that the modern age of weather forecasting began.
Before that, the fastest that distant weather reports could travel was around 160 kilometres per day (100 mi/d), but was more typically 60–120 kilometres per day (40–75 mi/day) (whether by land or by sea).
By the late 1840s, the telegraph allowed reports of weather conditions from a wide area to be received almost instantaneously, allowing forecasts to be made from knowledge of weather conditions further
upwind
Windward () and leeward () are terms used to describe the direction of the wind. Windward is ''upwind'' from the point of reference, i.e. towards the direction from which the wind is coming; leeward is ''downwind'' from the point of reference ...
.
The two men credited with the birth of forecasting as a science were an officer of the
Royal Navy
The Royal Navy (RN) is the United Kingdom's naval warfare force. Although warships were used by English and Scottish kings from the early medieval period, the first major maritime engagements were fought in the Hundred Years' War against ...
Francis Beaufort and his
protégé Robert FitzRoy
Vice-Admiral Robert FitzRoy (5 July 1805 – 30 April 1865) was an English officer of the Royal Navy and a scientist. He achieved lasting fame as the captain of during Charles Darwin's famous voyage, FitzRoy's second expedition to Tierra de ...
. Both were influential men in
British
British may refer to:
Peoples, culture, and language
* British people, nationals or natives of the United Kingdom, British Overseas Territories, and Crown Dependencies.
** Britishness, the British identity and common culture
* British English, ...
naval and governmental circles, and though ridiculed in the press at the time, their work gained scientific credence, was accepted by the Royal Navy, and formed the basis for all of today's weather forecasting knowledge.
Beaufort developed the
Wind Force Scale and Weather Notation coding, which he was to use in his journals for the remainder of his life. He also promoted the development of reliable tide tables around British shores, and with his friend
William Whewell, expanded weather record-keeping at 200 British
coast guard
A coast guard or coastguard is a maritime security organization of a particular country. The term embraces wide range of responsibilities in different countries, from being a heavily armed military force with customs and security duties to ...
stations.
Robert FitzRoy was appointed in 1854 as chief of a new department within the
Board of Trade to deal with the collection of weather data at sea as a service to
mariners. This was the forerunner of the modern
Meteorological Office
The Meteorological Office, abbreviated as the Met Office, is the United Kingdom's national weather service. It is an executive agency and trading fund of the Department for Business, Energy and Industrial Strategy and is led by CEO Penelope ...
.
All ship captains were tasked with collating data on the weather and computing it, with the use of tested instruments that were loaned for this purpose.
[Mellersh, H. E. L. (1968). FitzRoy of the Beagle. Hart-Davis. ]
A storm in October 1859 that caused the loss of the
''Royal Charter'' inspired FitzRoy to develop charts to allow predictions to be made, which he called ''"forecasting the weather"'', thus coining the term "weather forecast".
Fifteen land stations were established to use the
telegraph
Telegraphy is the long-distance transmission of messages where the sender uses symbolic codes, known to the recipient, rather than a physical exchange of an object bearing the message. Thus flag semaphore is a method of telegraphy, whereas p ...
to transmit to him daily reports of weather at set times leading to the first gale warning service. His warning service for shipping was initiated in February 1861, with the use of
telegraph communications. The first daily weather forecasts were published in ''
The Times
''The Times'' is a British daily national newspaper based in London. It began in 1785 under the title ''The Daily Universal Register'', adopting its current name on 1 January 1788. ''The Times'' and its sister paper '' The Sunday Times'' (f ...
'' in 1861.
In the following year a system was introduced of hoisting storm warning cones at the principal ports when a gale was expected.
The ''"Weather Book"'' which FitzRoy published in 1863 was far in advance of the scientific opinion of the time.
As the electric telegraph network expanded, allowing for the more rapid dissemination of warnings, a national observational network was developed, which could then be used to provide synoptic analyses. Instruments to continuously record variations in meteorological parameters using
photography
Photography is the art, application, and practice of creating durable images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. It is employe ...
were supplied to the observing stations from
Kew Observatory
The King's Observatory (called for many years the Kew Observatory) is a Grade I listed building in Richmond, London. Now a private dwelling, it formerly housed an astronomical and terrestrial magnetic observatory founded by King George III. T ...
– these cameras had been invented by
Francis Ronalds
Sir Francis Ronalds FRS (21 February 17888 August 1873) was an English scientist and inventor, and arguably the first electrical engineer. He was knighted for creating the first working electric telegraph over a substantial distance. In 1816 ...
in 1845 and his
barograph
A barograph is a barometer that records the barometric pressure over time in graphical form. This instrument is also used to make a continuous recording of atmospheric pressure. The pressure-sensitive element, a partially evacuated metal cylinde ...
had earlier been used by FitzRoy.
To convey accurate information, it soon became necessary to have a standard vocabulary describing clouds; this was achieved by means of a series of classifications first achieved by
Luke Howard in 1802, and standardized in the ''
International Cloud Atlas
The ''International Cloud Atlas'' or simply the ''Cloud Atlas'', is a cloud atlas that was first published in 1896 and has remained in print since. Its initial purposes included aiding the training of meteorologists and promoting more consisten ...
'' of 1896.
Numerical prediction
It was not until the 20th century that advances in the understanding of atmospheric physics led to the foundation of modern
numerical weather prediction
Numerical weather prediction (NWP) uses mathematical models of the atmosphere and oceans to predict the weather based on current weather conditions. Though first attempted in the 1920s, it was not until the advent of computer simulation in th ...
. In 1922, English scientist
Lewis Fry Richardson published "Weather Prediction By Numerical Process", after finding notes and derivations he worked on as an ambulance driver in World War I. He described therein how small terms in the prognostic fluid dynamics equations governing atmospheric flow could be neglected, and a finite differencing scheme in time and space could be devised, to allow numerical prediction solutions to be found.
Richardson envisioned a large auditorium of thousands of people performing the calculations and passing them to others. However, the sheer number of calculations required was too large to be completed without the use of computers, and the size of the grid and time steps led to unrealistic results in deepening systems. It was later found, through numerical analysis, that this was due to
numerical instability. The first computerised weather forecast was performed by a team composed of American meteorologists
Jule Charney, Philip Thompson, Larry Gates, and Norwegian meteorologist
Ragnar Fjørtoft
Ragnar Fjørtoft (1 August 1913 – 28 May 1998) was an internationally recognized Norwegian meteorologist. He was part of a Princeton, New Jersey team that in 1950 performed the first successful numerical weather prediction using the ENIAC el ...
, applied mathematician
John von Neumann
John von Neumann (; hu, Neumann János Lajos, ; December 28, 1903 – February 8, 1957) was a Hungarian-American mathematician, physicist, computer scientist, engineer and polymath. He was regarded as having perhaps the widest cove ...
, and
ENIAC
ENIAC (; Electronic Numerical Integrator and Computer) was the first programmable, electronic, general-purpose digital computer, completed in 1945. There were other computers that had these features, but the ENIAC had all of them in one pac ...
programmer
Klara Dan von Neumann. Practical use of numerical weather prediction began in 1955, spurred by the development of programmable electronic computers.
Broadcasts
The first ever daily weather forecasts were published in ''
The Times
''The Times'' is a British daily national newspaper based in London. It began in 1785 under the title ''The Daily Universal Register'', adopting its current name on 1 January 1788. ''The Times'' and its sister paper '' The Sunday Times'' (f ...
'' on August 1, 1861, and the first
weather maps were produced later in the same year. In 1911, the
Met Office began issuing the first marine weather forecasts via radio transmission. These included gale and storm warnings for areas around Great Britain. In the United States, the first public radio forecasts were made in 1925 by Edward B. "E.B." Rideout, on
WEEI, the Edison Electric Illuminating station in Boston.
Rideout came from the
U.S. Weather Bureau, as did
WBZ weather forecaster G. Harold Noyes in 1931.
The world's first
televised
Television, sometimes shortened to TV, is a telecommunication medium for transmitting moving images and sound. The term can refer to a television set, or the medium of television transmission. Television is a mass medium for advertising, ...
weather forecasts, including the use of weather maps, were experimentally broadcast by the
BBC #REDIRECT BBC #REDIRECT BBC
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...
in November 1936.
This was brought into practice in 1949, after
World War II
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposing ...
.
George Cowling gave the first weather forecast while being televised in front of the map in 1954.
In America, experimental television forecasts were made by James C. Fidler in Cincinnati in either 1940 or 1947 on the
DuMont Television Network.
In the late 1970s and early 80s,
John Coleman, the first weatherman on ABC-TV's ''
Good Morning America'', pioneered the use of on-screen
weather satellite
A weather satellite or meteorological satellite is a type of Earth observation satellite that is primarily used to monitor the weather and climate of the Earth. Satellites can be polar orbiting (covering the entire Earth asynchronously), or ...
information and
computer graphics
Computer graphics deals with generating images with the aid of computers. Today, computer graphics is a core technology in digital photography, film, video games, cell phone and computer displays, and many specialized applications. A great de ...
for television forecasts.
[CJR Rewind: Hot Air]
''Columbia Journalism Review
The ''Columbia Journalism Review'' (''CJR'') is a biannual magazine for professional journalists that has been published by the Columbia University Graduate School of Journalism since 1961. Its contents include news and media industry trends, an ...
'', reprint, first published in the January/February 2010 issue. Coleman was a co-founder of
The Weather Channel
The Weather Channel (TWC) is an American pay television channel owned by Weather Group, LLC, a subsidiary of Allen Media Group. The channel's headquarters are in Atlanta, Georgia. Launched on May 2, 1982, the channel broadcasts weather foreca ...
(TWC) in 1982. TWC is now a 24-hour cable network. Some weather channels have started broadcasting on
live broadcasting programs such as YouTube and
Periscope to reach more viewers.
How models create forecasts
The basic idea of numerical weather prediction is to sample the state of the fluid at a given time and use the equations of
fluid dynamics and
thermodynamics
Thermodynamics is a branch of physics that deals with heat, work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed by the four laws of th ...
to estimate the state of the fluid at some time in the future. The main inputs from country-based weather services are surface observations from automated
weather station
A weather station is a facility, either on land or sea, with instruments and equipment for measuring atmospheric conditions to provide information for weather forecasts and to study the weather and climate. The measurements taken include tempera ...
s at ground level over land and from weather buoys at sea. The
World Meteorological Organization
The World Meteorological Organization (WMO) is a specialized agency of the United Nations responsible for promoting international cooperation on atmospheric science, climatology, hydrology and geophysics.
The WMO originated from the Intern ...
acts to standardize the instrumentation, observing practices and timing of these observations worldwide. Stations either report hourly in
METAR reports, or every six hours in
SYNOP
SYNOP (surface synoptic observations) is a numerical code (called FM-12 by WMO) used for reporting weather observations made by manned and automated weather stations. SYNOP reports are typically sent every six hours by Deutscher Wetterdienst on s ...
reports. Sites launch
radiosonde
A radiosonde is a battery-powered telemetry instrument carried into the atmosphere usually by a weather balloon that measures various atmospheric parameters and transmits them by radio to a ground receiver. Modern radiosondes measure or calcula ...
s, which rise through the depth of the
troposphere
The troposphere is the first and lowest layer of the atmosphere of the Earth, and contains 75% of the total mass of the planetary atmosphere, 99% of the total mass of water vapour and aerosols, and is where most weather phenomena occur. From ...
and well into the
stratosphere. Data from
weather satellite
A weather satellite or meteorological satellite is a type of Earth observation satellite that is primarily used to monitor the weather and climate of the Earth. Satellites can be polar orbiting (covering the entire Earth asynchronously), or ...
s are used in areas where traditional data sources are not available. Compared with similar data from radiosondes, the satellite data has the advantage of global coverage, however at a lower accuracy and resolution.
Meteorological radar provide information on precipitation location and intensity, which can be used to estimate precipitation accumulations over time. Additionally, if a
pulse Doppler weather radar
Weather radar, also called weather surveillance radar (WSR) and Doppler weather radar, is a type of radar used to locate precipitation, calculate its motion, and estimate its type (rain, snow, hail etc.). Modern weather radars are mostly pulse- ...
is used then wind speed and direction can be determined. These methods, however, leave an in situ observational gap in the lower atmosphere (from 100 m to 6 km above ground level). To reduce this gap, in the late 1990s
weather drones started to be considered for obtaining data from those altitudes. Research has been growing significantly since the 2010s, and weather drones data may in future be added to numerical weather models.
Commerce provides
pilot report
A pilot report or PIREP is a report of actual flight or ground conditions encountered by an aircraft. Reports commonly include information about atmospheric conditions (like temperature, icing, turbulence) or airport conditions (like runway con ...
s along aircraft routes, and ship reports along shipping routes. Research flights using
reconnaissance aircraft fly in and around weather systems of interest such as
tropical cyclone
A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depen ...
s.
Reconnaissance aircraft are also flown over the open oceans during the cold season into systems that cause significant uncertainty in forecast guidance, or are expected to be of high impact 3–7 days into the future over the downstream continent.
Models are ''initialized'' using this observed data. The irregularly spaced observations are processed by
data assimilation and objective analysis methods, which perform quality control and obtain values at locations usable by the model's mathematical algorithms (usually an evenly spaced grid). The data are then used in the model as the starting point for a forecast. Commonly, the set of equations used to predict the physics and dynamics of the atmosphere are called
primitive equations. These equations are initialized from the analysis data and rates of change are determined. The rates of change predict the state of the atmosphere a short time into the future. The equations are then applied to this new atmospheric state to find new rates of change, and these new rates of change predict the atmosphere at a yet further time into the future. This ''time stepping'' procedure is continually repeated until the solution reaches the desired forecast time.
The length of the time step chosen within the model is related to the distance between the points on the computational grid, and is chosen to maintain
numerical stability. Time steps for global models are on the order of tens of minutes, while time steps for regional models are between one and four minutes. The global models are run at varying times into the future. The
Met Office's
Unified Model The Unified Model is a numerical weather prediction and climate modeling software suite originally developed by the United Kingdom Met Office, and now both used and further developed by many weather-forecasting agencies around the world. The Unif ...
is run six days into the future,
the
European Centre for Medium-Range Weather Forecasts
The European Centre for Medium-Range Weather Forecasts (ECMWF) is an independent intergovernmental organisation supported by most of the nations of Europe. It is based at three sites: Shinfield Park, Reading, United Kingdom; Bologna, Italy; an ...
model is run out to 10 days into the future, while the
Global Forecast System model run by the
Environmental Modeling Center is run 16 days into the future. The visual output produced by a model solution is known as a
prognostic chart, or ''prog''. The raw output is often modified before being presented as the forecast. This can be in the form of statistical techniques to remove known
biases in the model, or of adjustment to take into account consensus among other numerical weather forecasts. MOS or model output statistics is a technique used to interpret numerical model output and produce site-specific guidance. This guidance is presented in coded numerical form, and can be obtained for nearly all National Weather Service reporting stations in the United States. As proposed by
Edward Lorenz
Edward Norton Lorenz (May 23, 1917 – April 16, 2008) was an American mathematician and meteorologist who established the theoretical basis of weather and climate predictability, as well as the basis for computer-aided atmospheric physics and ...
in 1963, long range forecasts, those made at a range of two weeks or more, are impossible to definitively predict the state of the atmosphere, owing to the
chaotic nature of the
fluid dynamics equations involved. In numerical models, extremely small errors in initial values double roughly every five days for variables such as temperature and wind velocity.
Essentially, a model is a computer program that produces
meteorological information for future times at given locations and altitudes. Within any modern model is a set of equations, known as the primitive equations, used to predict the future state of the atmosphere. These equations—along with the
ideal gas law—are used to evolve the
density
Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematical ...
,
pressure
Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...
, and
potential temperature scalar fields and the
velocity
Velocity is the directional speed of an object in motion as an indication of its rate of change in position as observed from a particular frame of reference and as measured by a particular standard of time (e.g. northbound). Velocity i ...
vector field of the atmosphere through time. Additional transport equations for pollutants and other
aerosols are included in some primitive-equation mesoscale models as well. The equations used are
nonlinear partial differential equations, which are impossible to solve exactly through analytical methods,
with the exception of a few idealized cases. Therefore, numerical methods obtain approximate solutions. Different models use different solution methods: some global models use
spectral method
Spectral methods are a class of techniques used in applied mathematics and scientific computing to numerically solve certain differential equations. The idea is to write the solution of the differential equation as a sum of certain "basis function ...
s for the horizontal dimensions and
finite difference method
In numerical analysis, finite-difference methods (FDM) are a class of numerical techniques for solving differential equations by approximating derivatives with finite differences. Both the spatial domain and time interval (if applicable) are ...
s for the vertical dimension, while regional models and other global models usually use finite-difference methods in all three dimensions.
Techniques
Persistence
The simplest method of forecasting the weather, persistence, relies upon today's conditions to forecast the conditions tomorrow. This can be a valid way of forecasting the weather when it is in a steady state, such as during the summer season in the tropics. This method of forecasting strongly depends upon the presence of a stagnant weather pattern. Therefore, when in a fluctuating weather pattern, this method of forecasting becomes inaccurate. It can be useful in both short range forecasts and Long range weather forecast, long range forecasts.
Use of a barometer
Measurements of barometric pressure and the pressure tendency (the change of pressure over time) have been used in forecasting since the late 19th century. The larger the change in pressure, especially if more than , the larger the change in weather can be expected. If the pressure drop is rapid, a
low pressure system
In meteorology, a low-pressure area, low area or low is a region where the atmospheric pressure is lower than that of surrounding locations. Low-pressure areas are commonly associated with inclement weather (such as cloudy, windy, with possible ...
is approaching, and there is a greater chance of rain.
Rapid pressure rises are associated with improving weather conditions, such as clearing skies.
Looking at the sky
Along with pressure tendency, the condition of the sky is one of the more important parameters used to forecast weather in mountainous areas. Thickening of cloud cover or the invasion of a higher cloud deck is indicative of rain in the near future. High thin
cirrostratus cloud
Cirrostratus is a high-level, very thin, generally uniform ''stratiform'' genus-type of cloud. It is made out of ice-crystals, which are pieces of frozen water. It is difficult to detect and it can make halos. These are made when the cloud takes ...
s can create
halo
Halo, halos or haloes usually refer to:
* Halo (optical phenomenon)
* Halo (religious iconography), a ring of light around the image of a head
HALO, halo, halos or haloes may also refer to:
Arts and entertainment Video games
* ''Halo'' (franch ...
s around the
sun
The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
or
moon
The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
, which indicates an approach of a
warm front
A warm front is a density discontinuity located at the leading edge of a homogeneous warm air mass, and is typically located on the equator-facing edge of an isotherm gradient. Warm fronts lie within broader troughs of low pressure than cold f ...
and its associated rain. Morning
fog portends fair conditions, as rainy conditions are preceded by wind or clouds that prevent fog formation. The approach of a line of
thunderstorm
A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere, known as thunder. Relatively weak thunderstorms are some ...
s could indicate the approach of a
cold front
A cold front is the leading edge of a cooler mass of air at ground level that replaces a warmer mass of air and lies within a pronounced surface trough of low pressure. It often forms behind an extratropical cyclone (to the west in the Northern ...
. Cloud-free skies are indicative of fair weather for the near future. A
bar can indicate a coming tropical cyclone. The use of sky cover in weather prediction has led to various
weather lore
Weather lore is the body of informal folklore related to the prediction of the weather and its greater meaning.
Much like regular folklore, weather lore is passed down through speech and writing from normal people without the use of external me ...
over the centuries.
Nowcasting
The forecasting of the weather within the next six hours is often referred to as nowcasting. In this time range it is possible to forecast smaller features such as individual showers and thunderstorms with reasonable accuracy, as well as other features too small to be resolved by a computer model. A human given the latest radar, satellite and observational data will be able to make a better analysis of the small scale features present and so will be able to make a more accurate forecast for the following few hours. However, there are now
expert systems using those data and mesoscale numerical model to make better extrapolation, including evolution of those features in time.
Accuweather is known for a Minute-Cast, which is a minute-by-minute
precipitation
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...
forecast for the next two hours.
Use of forecast models
In the past, the human forecaster was responsible for generating the entire weather forecast based upon available observations. Today, human input is generally confined to choosing a model based on various parameters, such as model biases and performance.
[Klaus Weickmann, Jeff Whitaker, Andres Roubicek and Catherine Smith (December 1, 2001)]
"The Use of Ensemble Forecasts to Produce Improved Medium Range (3–15 days) Weather Forecasts"
Climate Diagnostics Center
The Earth System Research Laboratories (ESRL) is an alliance of four NOAA scientific labs, all located in the David Skaggs Research Center on the Department of Commerce campus in Boulder, Colorado. Organized under NOAA’s Office of Oceanic and ...
. Retrieved February 16, 2007. Using a consensus of forecast models, as well as ensemble members of the various models, can help reduce forecast error.
[Todd Kimberlain (June 2007)]
"TC Genesis, Track, and Intensity Forecating"
PowerPoint. Retrieved July 21, 2007. However, regardless how small the average error becomes with any individual system, large errors within any particular piece of guidance are still possible on any given model run. Humans are required to interpret the model data into weather forecasts that are understandable to the end user. Humans can use knowledge of local effects that may be too small in size to be resolved by the model to add information to the forecast. While increasing accuracy of forecast models implies that humans may no longer be needed in the forecast process at some point in the future, there is currently still a need for human intervention.
Analog technique
The analog technique is a complex way of making a forecast, requiring the forecaster to remember a previous weather event that is expected to be mimicked by an upcoming event. What makes it a difficult technique to use is that there is rarely a perfect analog for an event in the future. Some call this type of forecasting pattern recognition. It remains a useful method of observing rainfall over data voids such as oceans, as well as the forecasting of precipitation amounts and distribution in the future. A similar technique is used in medium range forecasting, which is known as teleconnections, when systems in other locations are used to help pin down the location of another system within the surrounding regime. An example of teleconnections are by using
El Niño-Southern Oscillation (ENSO) related phenomena.
Communicating forecasts to the public
Most end users of forecasts are members of the general public. Thunderstorms can create strong winds and dangerous
lightning
Lightning is a naturally occurring electrostatic discharge during which two electrically charged regions, both in the atmosphere or with one on the ground, temporarily neutralize themselves, causing the instantaneous release of an avera ...
strikes that can lead to deaths, power outages, and widespread hail damage. Heavy snow or rain can bring transportation and commerce to a stand-still, as well as cause flooding in low-lying areas. Excessive
heat
In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is ...
or
cold wave
A cold wave (known in some regions as a cold snap, cold spell or Arctic Snap) is a weather phenomenon that is distinguished by a cooling of the air. Specifically, as used by the U.S. National Weather Service, a cold wave is a rapid fall in tem ...
s can sicken or kill those with inadequate utilities, and droughts can impact water usage and destroy vegetation.
Several countries employ government agencies to provide forecasts and watches/warnings/advisories to the public to protect life and property and maintain commercial interests. Knowledge of what the end user needs from a weather forecast must be taken into account to present the information in a useful and understandable way. Examples include the
National Oceanic and Atmospheric Administration
The National Oceanic and Atmospheric Administration (abbreviated as NOAA ) is an United States scientific and regulatory agency within the United States Department of Commerce that forecasts weather, monitors oceanic and atmospheric conditio ...
's
National Weather Service (NWS) and
Environment Canada's
Meteorological Service (MSC). Traditionally, newspaper, television, and radio have been the primary outlets for presenting weather forecast information to the public. In addition, some cities had
weather beacons. Increasingly, the internet is being used due to the vast amount of specific information that can be found. In all cases, these outlets update their forecasts on a regular basis.
Severe weather alerts and advisories
A major part of modern weather forecasting is the severe weather alerts and advisories that the national weather services issue in the case that severe or hazardous weather is expected. This is done to protect life and property. Some of the most commonly known of severe weather advisories are the
severe thunderstorm
A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere, known as thunder. Relatively weak thunderstorms are somet ...
and
tornado warning
A tornado warning ( SAME code: TOR) is a severe weather warning product issued by regional offices of weather forecasting agencies throughout the world to alert the public when a tornado has been reported or indicated by weather radar within the ...
, as well as the
severe thunderstorm
A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere, known as thunder. Relatively weak thunderstorms are somet ...
and
tornado watch. Other forms of these advisories include winter weather, high wind,
flood
A flood is an overflow of water ( or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are an area of study of the discipline hydrol ...
,
tropical cyclone
A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depen ...
, and fog. Severe weather advisories and alerts are broadcast through the media, including radio, using emergency systems as the
Emergency Alert System, which break into regular programming.
Low temperature forecast
The low temperature forecast for the current day is calculated using the lowest temperature found between 7pm that evening through 7am the following morning. So, in short, today's forecasted low is most likely tomorrow's low temperature.
Specialist forecasting
There are a number of sectors with their own specific needs for weather forecasts and specialist services are provided to these users as given below:
Air traffic
Because the aviation industry is especially sensitive to the weather, accurate weather forecasting is essential. Fog or exceptionally low
ceilings can prevent many aircraft from landing and taking off.
Turbulence
In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to a laminar flow, which occurs when a fluid flows in parallel layers, with no disruption between ...
and
icing are also significant in-flight hazards. Thunderstorms are a problem for all aircraft because of severe turbulence due to their
updrafts and
outflow boundaries, icing due to the heavy precipitation, as well as large
hail, strong winds, and lightning, all of which can cause severe damage to an aircraft in flight.
Volcanic ash
Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, created during volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used to refer ...
is also a significant problem for aviation, as aircraft can lose engine power within ash clouds. On a day-to-day basis airliners are routed to take advantage of the
jet stream tailwind to improve fuel efficiency. Aircrews are briefed prior to
takeoff
Takeoff is the phase of flight in which an aerospace vehicle leaves the ground and becomes airborne. For aircraft traveling vertically, this is known as liftoff.
For aircraft that take off horizontally, this usually involves starting with a ...
on the conditions to expect en route and at their destination. Additionally, airports often change which
runway
According to the International Civil Aviation Organization (ICAO), a runway is a "defined rectangular area on a land aerodrome prepared for the landing and takeoff of aircraft". Runways may be a man-made surface (often asphalt, concre ...
is being used to take advantage of a
headwind
A tailwind is a wind that blows in the direction of travel of an object, while a headwind blows against the direction of travel. A tailwind increases the object's speed and reduces the time required to reach its destination, while a headwind has ...
. This reduces the distance required for takeoff, and eliminates potential
crosswind
A crosswind is any wind that has a perpendicular component to the line or direction of travel. This affects the aerodynamics of many forms of transport. Moving non-parallel to the wind's direction creates a crosswind component on the object and th ...
s.
Marine
Commercial and recreational use of waterways can be limited significantly by wind direction and speed,
wave
In physics, mathematics, and related fields, a wave is a propagating dynamic disturbance (change from equilibrium) of one or more quantities. Waves can be periodic, in which case those quantities oscillate repeatedly about an equilibrium (re ...
periodicity and heights, tides, and precipitation. These factors can each influence the safety of marine transit. Consequently, a variety of codes have been established to efficiently transmit detailed marine weather forecasts to vessel pilots via radio, for example the
MAFOR (marine forecast). Typical weather forecasts can be received at sea through the use of
RTTY,
Navtex and
Radiofax
Radiofacsimile, radiofax or HF fax is an analogue mode for transmitting monochrome images via high frequency (HF) radio waves. It was the predecessor to slow-scan television (SSTV). It was the primary method of sending photographs from remote s ...
.
Agriculture
Farmers rely on weather forecasts to decide what work to do on any particular day. For example, drying
hay is only feasible in dry weather. Prolonged periods of dryness can ruin cotton, wheat, and
corn crops. While corn crops can be ruined by drought, their dried remains can be used as a cattle feed substitute in the form of
silage
Silage () is a type of fodder made from green foliage crops which have been preserved by fermentation to the point of acidification. It can be fed to cattle, sheep and other such ruminants (cud-chewing animals). The fermentation and storage ...
.
Frosts and freezes play havoc with crops both during the spring and fall. For example,
peach
The peach (''Prunus persica'') is a deciduous tree first domesticated and cultivated in Zhejiang province of Eastern China. It bears edible juicy fruits with various characteristics, most called peaches and others (the glossy-skinned, non-f ...
trees in full bloom can have their potential peach crop decimated by a spring freeze. Orange groves can suffer significant damage during frosts and freezes, regardless of their timing.
Forestry
Weather forecasting of wind, precipitations and humidity is essential for preventing and controlling
wildfire
A wildfire, forest fire, bushfire, wildland fire or rural fire is an unplanned, uncontrolled and unpredictable fire in an area of combustible vegetation. Depending on the type of vegetation present, a wildfire may be more specifically identi ...
s. Different indices, like the ''
Forest fire weather index
The Forest fire weather index (FWI) (French: indice forêt météo, IFM) is an estimation of the risk of wildfire computed by Météo France and the Meteorological Service of Canada. It was introduced in France in 1992 but is based on a Canadian e ...
'' and the ''
Haines Index Haines Index (also known as Lower Atmosphere Severity Index) is a weather index developed by meteorologist Donald Haines in 1988 that measures the potential for dry, unstable air to contribute to the development of large or erratic wildland fires. ...
'', have been developed to predict the areas more at risk to experience fire from natural or human causes. Conditions for the development of harmful insects can be predicted by forecasting the evolution of weather, too.
Utility companies
Electricity and gas companies rely on weather forecasts to anticipate demand, which can be strongly affected by the weather. They use the quantity termed the degree day to determine how strong of a use there will be for heating (
heating degree day) or cooling (cooling degree day). These quantities are based on a daily average temperature of . Cooler temperatures force heating degree days (one per degree Fahrenheit), while warmer temperatures force cooling degree days. In winter, severe cold weather can cause a surge in demand as people turn up their heating. Similarly, in summer a surge in demand can be linked with the increased use of
air conditioning
Air conditioning, often abbreviated as A/C or AC, is the process of removing heat from an enclosed space to achieve a more comfortable interior environment (sometimes referred to as 'comfort cooling') and in some cases also strictly controlling ...
systems in hot weather. By anticipating a surge in demand, utility companies can purchase additional supplies of power or natural gas before the price increases, or in some circumstances, supplies are restricted through the use of
brownouts and
blackouts.
Other commercial companies
Increasingly, private companies pay for weather forecasts tailored to their needs so that they can increase their profits or avoid large losses. For example, supermarket chains may change the stocks on their shelves in anticipation of different consumer spending habits in different weather conditions. Weather forecasts can be used to invest in the commodity market, such as futures in oranges, corn, soybeans, and oil.
Military applications
United Kingdom Armed Forces
Royal Navy
The UK
Royal Navy
The Royal Navy (RN) is the United Kingdom's naval warfare force. Although warships were used by English and Scottish kings from the early medieval period, the first major maritime engagements were fought in the Hundred Years' War against ...
, working with the UK
Met Office, has its own specialist branch of weather observers and forecasters, as part of the Hydrographic and Meteorological (HM) specialisation, who monitor and forecast operational conditions across the globe, to provide accurate and timely weather and oceanographic information to submarines, ships and
Fleet Air Arm aircraft.
Royal Air Force
A mobile unit in the
RAF
The Royal Air Force (RAF) is the United Kingdom's air and space force. It was formed towards the end of the First World War on 1 April 1918, becoming the first independent air force in the world, by regrouping the Royal Flying Corps (RFC) and ...
, working with the UK Met Office, forecasts the weather for regions in which British, allied servicemen and women are deployed. A group based at
Camp Bastion provides forecasts for the British armed forces in
Afghanistan
Afghanistan, officially the Islamic Emirate of Afghanistan,; prs, امارت اسلامی افغانستان is a landlocked country located at the crossroads of Central Asia and South Asia. Referred to as the Heart of Asia, it is bordere ...
.
United States Armed Forces
US Navy
Similar to the private sector, military weather forecasters present weather conditions to the war fighter community. Military weather forecasters provide pre-flight and in-flight weather briefs to pilots and provide real time resource protection services for military installations. Naval forecasters cover the waters and ship weather forecasts. The
United States Navy
The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage ...
provides a special service to both themselves and the rest of the federal government by issuing forecasts for tropical cyclones across the Pacific and Indian Oceans through their
Joint Typhoon Warning Center.
US Air Force
Within the United States, Air Force Weather provides weather forecasting for the Air Force and the Army.
Air Force
An air force – in the broadest sense – is the national military branch that primarily conducts aerial warfare. More specifically, it is the branch of a nation's armed services that is responsible for aerial warfare as distinct from an ...
forecasters cover air operations in both wartime and peacetime operations and provide
Army
An army (from Old French ''armee'', itself derived from the Latin verb ''armāre'', meaning "to arm", and related to the Latin noun ''arma'', meaning "arms" or "weapons"), ground force or land force is a fighting force that fights primarily on ...
support;
United States Coast Guard
The United States Coast Guard (USCG) is the maritime security, search and rescue, and law enforcement service branch of the United States Armed Forces and one of the country's eight uniformed services. The service is a maritime, military, mu ...
marine science technicians provide ship forecasts for ice breakers and other various operations within their realm; and Marine forecasters provide support for ground- and air-based
United States Marine Corps
The United States Marine Corps (USMC), also referred to as the United States Marines, is the maritime land force service branch of the United States Armed Forces responsible for conducting expeditionary and amphibious operations through combi ...
operations. All four military branches take their initial enlisted meteorology technical training at
Keesler Air Force Base.
[ Keesler Air Force Base. Military officers usually received their education from a civilian institution]
"Keesler News: March 9, 2006"
. United States Air Force
The United States Air Force (USAF) is the Aerial warfare, air military branch, service branch of the United States Armed Forces, and is one of the eight uniformed services of the United States. Originally created on 1 August 1907, as a part ...
Retrieved May 26, 2008. Military and civilian forecasters actively cooperate in analyzing, creating and critiquing weather forecast products.
See also
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Air pollution forecasting
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Citizen Weather Observer Program
The Citizen Weather Observer Program (CWOP) is a network of privately owned electronic weather stations concentrated in the United States but also located in over 150 countries. Network participation allows volunteers with computerized weather sta ...
*
Ensemble forecasting
*
National Collegiate Weather Forecasting Contest
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National Weatherperson's Day
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Tropical cyclone forecasting
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Weather and Society Integrated Studies
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Weather hole
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WxChallenge
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Weather forecasting for Operation Overlord
The Overlord planners for the invasion of Europe in 1944 specified suitable weather (wind, cloud, tidal and moon conditions) for the assault landing; with only a few days in each month suitable. In May and June 1944 frequent pre-assault meetings we ...
References
Further reading
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External links
Meteorological agencies
These are academic or governmental meteorology organizations. Most provide at least a limited forecast for their area of interest on their website.
The World Meteorological OrganizationEuropean Centre for Medium Range Weather Forecasting (ECMWF)European Meteorological Satellites
Australian Bureau of MeteorologyRoyal Meteorological Institute of BelgiumEnvironment Canada Weather Office
French National Meteorological Service
Indian Meteorological Department (IMD)National Centre for Medium Range Weather Forecast (NCMRWF)Indian Institute of Tropical Meteorology (IITM)
National Atmospheric Research Laboratory (NARL)Pakistan Meteorological DepartmentThe Hellenic National Meteorological Service (Greece)Hong Kong ObservatoryMet Éireann (Ireland)Italian Air Force (Aeronautica Militare) Meteorological ServiceKorea Meteorological AdministrationNew Zealand MetService
The Met Office of the UKyr.no (a joint online weather service from the Norwegian Meteorological Institute (met.no) and the Norwegian Broadcasting Corporation (NRK))
Unidad de Meteorología – IVIC (Meteorology Unit – Venezuela Institute of Scientific Research)
Instituto Nacional de Hidrometeorología
National Meteorological Service of Sloveniabased on
Academa Application server and WebMet
Centro de Previsão de Tempo e Estudos Climáticosa
INPE(Brazil)
National Weather ServiceUnited States of America
National Meteorological Center��China)
The Israel Meteorological Service (IMS)
Other external links
Economic history and impact of weather forecastingfrom EH.net
Dynamic Weather ForecasterIowa State University's online educational tool for weather forecasting
"World Weather News by Radio"''Popular Mechanics'', January 1930, pp. 50–55, article on international weather report systems set up after World War One, using wireless broadcasting from various stations and ships worldwide
New Technology Allows Better Extreme Weather Forecasts; New technology that increases the warning time for tornadoes and hurricanes could potentially save hundreds of lives every yearApril 17, 2012
Current aviation weather charts for the Americas, Europe, Asia, Africa, the Atlantic and Pacific oceansWeather Forecasting Through the AgesHistory of meteorologyWelcome to the ICHM
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