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Information about Weather Forecasting

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Weather
 
Seasons
Temperate
• Spring • Summer •
• Autumn • Winter •
Tropical
• Dry season •
• Wet season
Storms
• Thunderstorm • Tornado •
• Tropical Cyclone (Hurricane) •
• Winter storm • Blizzard
Precipitation
• Fog • Drizzle • Rain •
• Freezing rain • Sleet •
• Hail • Snow
Topics
• Meteorology •
• Weather forecasting •
• Climate • Air pollution •
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Modern weather predictions aid in timely evacuations and potentially save lives and property damage
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Weather map of Europe, 10 December 1887
Weather forecasting is the application of science and technology to predict the state of the atmosphere for a future time and a given location.

Human beings have attempted to predict the weather since time immemorial. Today, weather forecasts are made by collecting quantitative data about the current state of the atmosphere and using scientific understanding of atmospheric processes to project how the atmosphere will evolve. The chaotic nature of the atmosphere, the massive computational power required to solve the equations that describe the atmosphere, and incomplete understanding of atmospheric processes mean that forecasts become less accurate as the difference in time between the present moment and the time for which the forecast is being made (the range of the forecast) increases.

History of weather forecasting

See also: Weather lore
For millennia people have tried to forecast the weather. In 650 BC, the Babylonians predicted the weather from cloud patterns. In about 340 BC, Aristotle described weather patterns in Meteorologica. Chinese weather prediction lore extends at least as far back as 300 BC.

Ancient weather forecasting methods usually relied on observed patterns of events. For example, it might be 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. However, not all of these predictions prove reliable and many of them have since been found not to stand up to rigorous statistical testing.[1]

It was not until the invention of the telegraph in 1837 that the modern age of weather forecasting began. Before this time, it had not been possible to transport information about the current state of the weather any faster than a steam train. The telegraph allowed reports of weather conditions from a wide area to be received almost instantaneously by the late 1840's.[2] This allowed forecasts to be made by knowing what the weather conditions were like further upwind.
Imagine a rotating sphere that is 12,800 kilometers (8000 miles) in diameter, has a bumpy surface, is surrounded by a 40-kilometer-deep mixture of different gases whose concentrations vary both spatially and over time, and is heated, along with its surrounding gases, by a nuclear reactor 150 million kilometers (93 million miles) away. Imagine also that this sphere is revolving around the nuclear reactor and that some locations are heated more during one part of the revolution and other locations are heated during another part of the revolution. And imagine that this mixture of gases continually receives inputs from the surface below, generally calmly but sometimes through violent and highly localized injections. Then, imagine that after watching the gaseous mixture, you are expected to predict its state at one location on the sphere one, two, or more days into the future. This is essentially the task encountered day by day by a weather forecaster.
On the difficulty of weather forecasting, Bob Ryan, Bulletin of the American Meteorological Society, 1982.
The two men most credited with the birth of forecasting as a science were Francis Beaufort (remembered chiefly for the Beaufort scale) and his protégé Robert Fitzroy (developer of the Fitzroy barometer). Both were influential men in British Naval and Governmental circles, and though ridiculed in the press at the time, their work gained scientific credence, was accepted by the British Navy and formed the basis for all of today's weather forecasting knowledge.[3]

Great progress was made in the science of meteorology during the 20th century. The possibility of numerical weather prediction was proposed by Lewis Fry Richardson in 1922, though computers fast enough to complete the vast number of calculations required to produce a forecast before the event had occurred did not exist at that time. Practical use of numerical weather prediction began in 1955,[4] spurred by the development of programmable electronic computers.

Modern day weather forecasting system

Components of a modern weather forecasting system include:
  • Data collection
  • Data assimilation
  • Numerical weather prediction
  • Model output post-processing
  • Forecast presentation to end-user

Data collection

Observations of atmospheric pressure, temperature, wind speed, wind direction, humidity, precipitation are made near the earth's surface by trained observers, automatic weather stations or buoys. The World Meteorological Organization 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 reports.

Measurements of temperature, humidity and wind above the surface are found by launching radiosondes (weather balloon). Data are usually obtained from near the surface to the middle of the stratosphere, about 30,000 m (100,000 ft). In recent years, data transmitted from commercial airplanes through the AMDAR system has also been incorporated into upper air observation, primarily in numerical models.

Increasingly, data from weather satellites are being used due to their (almost) global coverage. Although their visible light images are very useful for forecasters to see development of clouds, little of this information can be used by numerical weather prediction models. The infra-red (IR) data however can be used as it gives information on the temperature at the surface and cloud tops. Individual clouds can also be tracked from one time to the next to provide information on wind direction and strength at the clouds steering level. Polar orbiting satellites provide soundings of temperature and moisture throughout the depth of the atmosphere. Compared with similar data from radiosondes, the satellite data has the advantage that coverage is global, however the accuracy and resolution is not as good.

Meteorological radar provide information on precipitation location and intensity. Additionally, if doppler radar are used then wind speed and direction can be determined.[5]

Data assimilation

Main article: Data assimilation


During the data assimilation process, information gained from the observations is used in conjunction with a numerical model's most recent forecast for the time that observations were made (since this contains information from previous observations) to produce the meteorological analysis. This is the best estimate of the current state of the atmosphere. It is a three dimensional representation of the distribution of temperature, moisture and wind.

Numerical weather prediction (NWP)

Main article: Numerical weather prediction
Numerical weather prediction models are computer simulations of the atmosphere. They take the analysis as the starting point and evolve the state of the atmosphere forward in time using understanding of physics and fluid dynamics. The complicated equations which govern how the state of a fluid changes with time require supercomputers to solve them. The output from the model provides the basis of the weather forecast.[6]

Model output post processing

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.

In the past, the human forecaster used to be responsible for generating the entire weather forecast from the observations. However today, for forecasts beyond 24hrs human input is generally confined to post-processing of model data to add value to the forecast. Humans are required to interpret the model data into weather forecasts that are understandable to the end user. Additionally, humans can use knowledge of local effects which may be too small in size to be resolved by the model to add information to the forecast. Increasing accuracy of forecast models continues to decrease the need for post-processing and human input, mostly in areas with a low variation in terrain.

Presentation of weather forecasts

An example of a two-day weather forecast in the visual style that an American newspaper might use.


The final stage in the forecasting process is perhaps the most important. 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.

Public information

One of the main end users of a forecast is the general public. Thunderstorms can cause strong winds, dangerous lightning strikes leading to deaths and power outages,[7] 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 or cold waves can kill or sicken those without adequate utilities. The National Weather Service provides forecasts and watches/warnings/advisories for all areas of the United States to protect life and property and maintain commercial interests.[8] Environment Canada is responsible for dispensing similar forecasts and warnings to the public in Canada.[9] Traditionally, television and radio weather presenters have been the main method of informing the public, however increasingly the internet is being used due to the vast amount of information that can be found.

Air traffic

The aviation industry is especially sensitive to the weather. Fog and/or exceptionally low ceilings can prevent many aircraft landing and taking off. Similarly, turbulence and icing can be hazards whilst in flight. Thunderstorms are a problem for all aircraft, due to severe turbulence and icing, as well as large hail, strong winds, and lightning, all of which can cause fatal damage to an aircraft in flight. 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 take off on the conditions to expect en route and at their destination. Additionally, runway orientation is often changed to take advantage of a headwind to generate lift for takeoff.

Marine

Commercial and recreational use of waterways can be limited significantly by weather in that wind direction and speed, wave periodicity and heights, tides, and precipitation 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).

Agriculture

Farmers rely on weather forecasts to decide what work to do. For example, cutting hay is only feasible in dry weather.

Utility companies

Electricity and gas companies rely on weather forecasts to anticipate demand which can be strongly affected by the weather. 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 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.

Private sector

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. State Departments of Transportation and private road maintenance companies also use their forecasts to demonstrate a 'best effort' in defending against lawsuits as a result of traffic accidents.

Military applications

Similarly to the private sector, military weather forecasters present weather conditions to the war fighter community. They provide pre-flight weather briefs and flight weather briefs from take off to terminal location, including updates throughout the flight path. Also, military weather forecasters provide real time resource protection services for military installations. Four branches of the armed forces have independent weather forecasting techniques tailored for their specific needs: Naval forecasters cover the waters and ship weather forecasts; Air Force forecasters cover air operations in both wartime and peacetime operations and provide Army support; Coast Guard forecasters provide ship forecasts for ice breakers and other various operations within their realm; and Marine forecasters provide support for ground- and air-based Marine Corps operations. All four military branches take their initial meteorology training at Keesler AFB, MS. Military and civilian forecasters actively cooperate in analyzing, creating and critiquing weather forecast products.

Persistence forecasting

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 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. It can be useful in both short range forecasts and long range forecasts.[10]

Nowcasting

The forecasting of the weather in the 0-12 hour timeframe is often referred to as nowcasting. It is in this range that the human forecaster still has an advantage over computer NWP models. In this time range it is possible to forecast smaller features such as individual shower clouds with reasonable accuracy, however these are often 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.[11]

Below is a sample nowcast, issued by the National Weather Service in Mount Holly, New Jersey:

000 FPUS71 KPHI 240805 NOWPHI

SHORT TERM FORECAST NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 405 AM EDT FRI JUN 24 2005 DEZ002>004-MDZ015-019-020-NJZ013-014-020-022>027-241200- ATLANTIC NJ-ATLANTIC COASTAL CAPE MAY NJ-CAPE MAY NJ-CAROLINE MD- COASTAL ATLANTIC NJ-COASTAL OCEAN NJ-DELAWARE BEACHES DE- EASTERN MONMOUTH NJ-INLAND SUSSEX DE-KENT DE-OCEAN NJ- QUEEN ANNE'S MD-SOUTHEASTERN BURLINGTON NJ-TALBOT MD- WESTERN MONMOUTH NJ- INCLUDING THE CITIES OF...ATLANTIC CITY AND DOVER 405 AM EDT FRI JUN 24 2005

.NOW...

AREAS OF FOG AND LOW CLOUDS WILL BE OVER SOUTHERN DELAWARE AND PORTIONS OF THE NORTHEASTERN MARYLAND SHORE EARLY THIS MORNING, AS WELL AS ALONG THE NEW JERSEY COAST. THE PATCHY DENSE FOG MAY REDUCE THE VISIBILITY TO A QUARTER MILE OR LESS AT TIMES. IF YOU WILL BE DRIVING THIS MORNING, BE SURE TO LEAVE PLENTY OF ROOM BETWEEN YOUR VEHICLE AND THE ONE AHEAD OF YOU. YOUR VISIBILITY COULD DROP QUICKLY IF YOU DRIVE INTO A DENSE PATCH OF FOG. WATCH ESPECIALLY FOR PEDESTRIANS. THE FOG SHOULD DISSIPATE AN HOUR OR TWO AFTER SUNRISE. $$

Medium Range Forecasting

Analog technique

A more complicated way of making a forecast, it requires remembering a previous weather event which 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.[12] Some call this type of forecasting pattern recognition, which remains a useful method of observing rainfall over data voids such as oceans,[13] as well as the forecasting of precipitation amounts and distribution in the future. A variation on this theme is used in Medium Range forecasting, which is known as teleconnections, when you use systems in other locations to help pin down the location of another system within the surrounding regime.[14] One method of using teleconnections are by using ENSO-related phenomena.[15]

Ensemble forecasting

Although a forecast model will predict realistic looking weather features evolving realistically into the distant future, the errors in a forecast will inevitably grow with time due to the chaotic nature of the atmosphere. The detail that can be given in a forecast therefore decreases with time as these errors increase. There becomes a point when the errors are so large that the forecast is completely wrong and the forecast atmospheric state has no correlation with the actual state of the atmosphere.

However, looking at a single forecast gives no indication of how likely that forecast is to be correct. Ensemble forecasting uses lots of forecasts produced to reflect the uncertainty in the initial state of the atmosphere (due to errors in the observations and insufficient sampling). The uncertainty in the forecast can then be assessed by the range of different forecasts produced. They have been shown to be better at detecting the possibility of extreme events at long range.

Ensemble forecasts are increasingly being used for operational weather forecasting (for example at ECMWF, NCEP, and the Canadian forecasting center). [16]

See also

References

1. ^ Jerry Wilson. Skywatch Signs of the Weather. Retrieved on 2007-04-15.
2. ^ Encyclopedia Brittanica. Telegraph. Retrieved on 2007-05-05.
3. ^ Eric D. Craft. An Economic History of Weather Forecasting. Retrieved on 2007-04-15.
4. ^ Paul N. Edwards. Atmospheric General Circulation Modeling. Retrieved on 2007-02-16.
5. ^ University of Washington. An improving forecast. Retrieved on 2007-04-15.
6. ^ United Kingdom Met Office. Numerical weather prediction. Retrieved on 2007-02-16.
7. ^ University of Illinois at Urbana-Champaign. Lightning. Retrieved on 2007-02-16.
8. ^ National Weather Service. About NOAA's National Weather Service. Retrieved on 2007-02-16.
9. ^ Environment Canada. Main website. Retrieved on 2007-02-16.
10. ^ University of Illinois at Urbana-Champaign. Persistence Forecasting: Today equals Tomorrow. Retrieved on 2007-02-16.
11. ^ E-notes.com. Weather and Climate | What Is Nowcasting? Retrieved on 2007-02-16.
12. ^ Other Forecasting Methods: climatology, analogue and numerical weather prediction. Retrieved on 2006-02-16.
13. ^ Kenneth C. Allen. Pattern Recognition Techniques Applied to the NASA-ACTS Order-Wire Problem. Retrieved on 2007-02-16.
14. ^ Weather Associates, Inc. The Role of Teleconnections & Ensemble Forecasting in Extended- to Medium-Range Forecasting. Retrieved on 2007-02-16.
15. ^ Thinkquest.org. Teleconnections: Linking El Niño with Other Places. Retrieved on 2007-02-16.
16. ^ Klaus Weickmann, Jeff Whitaker, Andres Roubicek and Catherine Smith. The Use of Ensemble Forecasts to Produce Improved Medium Range (3-15 days) Weather Forecasts. Retrieved on 2007-02-16.

Websites providing forecasts

Meteorological agencies

These are academic or governmental meteorology organizations. Most provide at least a limited forecast for their area of interest on their website.

Commercial organisations

These are high profile commercial sites.
  • Foreca World Weather — Detailed weather forecast for all the countries in the world (except some microstates). In English.
  • Freese-Notis Weather Site — Meteorologists with doppler radar images, data analysis, forensics and a wide variety industry specific US and international weather forecasts, agriculture and energy being strong areas of performance plus supplies advanced web site content with an emphasis upon long range weather forecasts
  • Weather Underground — Provides a wide variety of US and international weather information
  • Unisys Weather Site — Provides meteorological data, analysis, and forecasts for the US along with ancillary information for aircraft or flight systems related information domestically and overseas particular skills in software for commercial applications
  • Verizon's Weather Forecasts - Provides weather briefs & extended outlook for the U.S. Also powers weather on 20,000 other websites
  • Meteo Webcam - A Italian language site displaying all webcam live from all the world and other utility resources.
  • MeteoGrouphttp://www.meteogroup.com Europe's largest independent weather forecasting company. Provides weather for Transport, Energy, Agriculture, Maritime, Media, Leisure, Health & Environment, Insurance and Water Management.
  • Accuweather — Weather forecasts and weather-related news (US and international) known for television grade services
  • The Weather Channel — Weather forecasts and weather-related news mainly for the US, but also has world forecasts. Also provides services to media organizations.
  • TheWeatherOutlook — Weather forecasts for the UK.
  • BBC Weather — Weather forecasts for the UK and climate overviews for the whole world. Links to contemporary climate change news for astute observers of the controversial topic
  • GMTV Weather Centre — Weathergirls Clare Nasir and Andrea McLean with the latest weather forecasts from the UK and around the world.
  • Wetterzentrale - A German language site displaying a large range of high quality weather charts.
  • The Weather Network - Canadian weather and forecasts.
  • Weatherzone - Provides a wide variety of Australian weather information.
  • Weather.com.au - Australian weather forecasts.
  • Weatheronline - Meteorological data, analysis, and forecasts for the UK and the whole world. Provides radar images, climate data and weather-related news.
  • MSN Weather (Data provided by FORECA) - Worldwide Weather Forecasts (Hourly, Extended Ten-day and Historical Averages)
  • ClearPoint Weather - World-Wide, Location-Specific, Weather Forecasts and Information - Including High Definition Weather For Today's Global Mariner.

Severe Weather alerts and advisories

A major part of modern weather forecasting is the severe weather alerts and advisories which the National Weather Services issues in the case that severe or hazardous weather is expected. Some of the most commonly known of the long list of severe weather advisories is the Severe thunderstorm and tornado warning, as well as the severe weather or the tornado watch. Other forms of these advisories include winter weather, high wind, flood, tropical storm, hurricane, fog and more. Severe weather advisories and alerts are somtimes broadcast through the NOAA weather radio.

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Nature, in the broadest sense, is equivalent to the natural world, physical universe, material world or material universe. "Nature" refers to the phenomena of the physical world, and also to life in general.
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weather is the set of all extant phenomena in a given atmosphere at a given time. The term usually refers to the activity of these phenomena over short periods (hours or days), as opposed to the term climate, which refers to the average atmospheric conditions over longer periods of
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Seasons

Temperate
Spring
Summer
Autumn
Winter
Tropical
Dry
season Cool
Hot
Wet season

A season is one of the major divisions of the year, generally based on yearly periodic changes in weather.
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temperate latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally mild, rather than extreme hot or cold. However, a temperate climate can have very unpredictable weather.
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Seasons

Temperate
Spring
Summer
Autumn
Winter
Tropical
Dry
season Cool
Hot
Wet season

Spring
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Summer is one of the four seasons of the year. In the West, the seasons are generally considered to start at the equies and solstices, based on astronomical reckoning. In English-language calendars, based on astronomy, summer begins on the day of the summer solstice and ends on the
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Autumn (also known as Fall in North American English) is one of the four temperate seasons. Autumn marks the transition from summer into winter. In the northern hemisphere, the start of autumn is generally considered to be around September and in the southern hemisphere, its
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Winter is one of the four seasons of temperate zones. Almost all English-language calendars, going by astronomy, state that winter begins on the winter solstice, and ends on the spring equinox.
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tropics are the geographic region of the Earth centered on the equator and limited in latitude by the Tropic of Cancer in the northern hemisphere, at approximately 23°30' (23.5°) N latitude, and the Tropic of Capricorn in the southern hemisphere at 23°30' (23.5°) S latitude.
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For the 2006 Chadian film, see .


The Dry season is a term commonly used when describing the weather in the tropics. The weather in the tropics is dominated by the tropical rain belt, which oscillates from the northern to the southern tropics over
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A Wet season or rainy season is a season in which the average rainfall in a region is significantly increased. The term green season is also sometimes used as a euphemism by tourist authorities. These terms are commonly used describing the weather in the tropics.
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storm is any disturbed state of an astronomical body's atmosphere, especially affecting its surface, and strongly implying severe weather. It may be marked by strong wind, thunder and lightning (a thunderstorm), heavy precipitation, such as ice (ice storm), or wind transporting
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thunderstorm, also called an electrical storm or lightning storm, is a form of weather characterized by the presence of lightning and its attendant thunder produced from a cumulonimbus cloud.
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tornado is a violently rotating column of air which is in contact with both a cumulonimbus cloud or, in rare cases, a cumulus cloud base and the surface of the earth. Tornadoes come in many sizes but are typically in the form of a visible condensation funnel, whose narrow end
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tropical cyclone is a meteorological term for a storm system characterized by a low pressure system center and thunderstorms that produces strong wind and flooding rain. A tropical cyclone feeds on the heat released when moist air rises and the water vapor it contains condenses.
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winter storm is a meteorological event in which the dominant varieties of precipitation are forms that only occur at cold temperatures, such as snow or sleet, or a rainstorm where ground temperatures are cold enough to allow ice to form (i.e. freezing rain).
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blizzard is a severe winter storm condition characterized by low temperatures, strong winds, and heavy blowing snow. Blizzards are formed when a high pressure system, also known as a ridge, interacts with a low pressure system; this results in the advection of air from the high
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precipitation (also known as hydrometeor) is any product of the condensation of atmospheric water vapor that is deposited on the earth's surface. It occurs when the atmosphere (being a large gaseous solution) becomes saturated with water vapour and the water condenses and
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FOG can be an acronym for...
  • the tool "Flexible Object Generator"
  • the tool "Fragmented-Object Generator"
  • Fiber Optic Gulf - a submarine telecommunications cable linking the United Arab Emirates, Qatar, Bahrain, and Kuwait
  • Fibre optic gyroscope

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Drizzle is light precipitation consisting of liquid water drops smaller than that of rain, and generally smaller than 0.5 mm (0.02 in.) in diameter.
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Rain is a type of precipitation, a product of the condensation of atmospheric water vapor that is deposited on the earth's surface. It forms when separate drops of water fall to the Earth's surface from clouds.
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Freezing Rain is a type of precipitation that begins as snow at higher altitude, falling from a cloud towards earth, melts completely on its way down while passing through a layer of air above freezing temperature, and then
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Sleet is a term used in a variety of ways to describe precipitation intermediate between rain and snow but distinct from hail.
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Hail is a form of precipitation which consists of balls or irregular lumps of ice (hailstones). Hailstones on Earth usually consist mostly of water ice and measure between 5 and 50 millimetres in diameter, with the larger stones coming from severe thunderstorms.
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SNOW 1.0 and 2.0 are two word-based synchronous stream ciphers developed by Thomas Johansson and Patrik Ekdahl at Lund University.

SNOW 1.0, originally simply SNOW, was submitted to the NESSIE project.
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Meteorology (from Greek: μετέωρον, meteoron, "high in the sky"; and λόγος, logos, "knowledge") is the interdisciplinary scientific study of the atmosphere that focuses on weather processes and
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Climate is the average and variations of weather over long periods of time. Climate zones can be defined using parameters such as temperature and rainfall.
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weather is the set of all extant phenomena in a given atmosphere at a given time. The term usually refers to the activity of these phenomena over short periods (hours or days), as opposed to the term climate, which refers to the average atmospheric conditions over longer periods of
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Earth's atmosphere is a layer of gases surrounding the planet Earth and retained by the Earth's gravity. It contains roughly (by molar content/volume) 78% nitrogen, 20.95% oxygen, 0.93% argon, 0.
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