Weather forecasting 73231 226094582 2008-07-16T20:16:03Z Pierre cb 846678 /* Data collection */ [[Image:Day5pressureforecast.gif|thumb|right|250 px|Forecast of surface pressures five days into the future for the north Pacific, North America, and north Atlantic ocean.]] '''Weather forecasting''' is the application of science and technology to predict the state of the [[Earth's atmosphere|atmosphere]] for a future time and a given location. Human beings have attempted to predict the [[weather]] informally for millennia, and formally since at least the nineteenth century. Weather forecasts are made by collecting quantitative [[data]] about the current state of the atmosphere and using [[meteorology|scientific understanding of atmospheric processes]] to project how the atmosphere will evolve. Once an all human endeavor based mainly upon changes in [[Atmospheric pressure|barometric pressure]], current weather conditions, and sky condition, [[numerical weather prediction|forecast models]] are now used to determine future conditions. Human input is still required to pick the best possible forecast model to base the forecast upon, which involves pattern recognition skills, [[teleconnection]]s, knowledge of model performance, and knowledge of model biases. The [[chaos theory|chaotic]] nature of the atmosphere, the massive computational power required to solve the equations that describe the atmosphere, error involved in measuring the initial conditions, and an incomplete understanding of atmospheric processes mean that forecasts become less accurate as the difference in 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 pick the most likely outcome. There are a variety of end users to weather forecasts. Weather warnings are important forecasts because they are used to protect life and property. Forecasts based on [[temperature]] and [[Precipitation (meteorology)|precipitation]] are important to [[agriculture]], and therefore to commodity traders within stock markets. Temperature forecasts are used by utility companies to estimate demand over coming days. On an everyday basis, people use weather forecasts to determine what to wear on a given day. Since outdoor activities are severely curtailed by heavy [[rain]], [[snow]] and the [[wind chill]], forecasts can be used to plan activities around these events, and to plan ahead and survive them. {{TOCLimit|limit=3}} == History == [[Image:Meyers b16 s0570.jpg|right|thumb|Weather map of [[Europe]], [[10 December]] [[1887]] ]] For millennia people have tried to forecast the weather. In 650 BC, the [[Babylonia|Babylonians]] predicted the weather from [[cloud]] patterns as well as [[astrology]].<ref>Mistic House. [http://www.mistichouse.com/astrology-lessons.htm Astrology Lessons, History, Predition, Skeptics, and Astrology Compatibility.] Retrieved on [[2008-01-12]].</ref> In about 340 BC, [[Aristotle]] described weather patterns in ''[[Meteorology (Aristotle)|Meteorologica]]''. [[China|Chinese]] weather prediction lore extends at least as far back as 300 BC.<ref>[[University of California]] Museum of Paleontology. [http://www.ucmp.berkeley.edu/history/aristotle.html Aristotle (384-322 B.C.E.).] Retrieved on [[2008-01-12]].</ref> Ancient weather forecasting methods usually relied on observed patterns of events, also termed pattern recognition. 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.<ref>Jerry Wilson. [http://wilstar.com/skywatch.htm#clouds Skywatch Signs of the Weather.] Retrieved on [[2007-04-15]].</ref> It was not until the invention of the [[Electrical telegraph|electric telegraph]] in 1835 that the modern age of weather forecasting began.<ref>{{cite web| url=http://www.si.edu/archives/ihd/jhp/joseph20.htm| title=Joseph Henry: Inventor of the Telegraph? Smithsonian Institution | accessdate=2006-06-29}}</ref> 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 1840s.<ref>Encyclopedia Brittanica. [http://www.britannica.com/eb/topic-585850/telegraph Telegraph.] Retrieved on [[2007-05-05]].</ref> This allowed forecasts to be made by knowing what the weather conditions were like further [[Windward and leeward|upwind]]. 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 [[United Kingdom of Great Britain and Ireland|British]] 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.<ref>Eric D. Craft. [http://eh.net/encyclopedia/article/craft.weather.forcasting.history An Economic History of Weather Forecasting.] Retrieved on [[2007-04-15]].</ref> 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,<ref>Lynch, P. (2006). The Emergence of Numerical Weather Prediction. Cambridge U.P.</ref> though computers did not exist to complete the vast number of calculations required to produce a forecast before the event had occurred. Practical use of numerical weather prediction began in 1955,<ref>Paul N. Edwards. [http://www.aip.org/history/sloan/gcm/ Atmospheric General Circulation Modeling.] Retrieved on [[2007-02-16]].</ref> spurred by the development of programmable electronic [[computer]]s. ==How models create forecasts== ===Data collection=== {{Main article|Numerical weather prediction|Weather station|Radiosonde|Weather satellite}} [[Surface weather observation]]s of atmospheric pressure, temperature, [[wind]] speed and direction, [[humidity]], precipitation are made near the earth's surface by trained observers, [[automatic weather station]]s or [[weather buoy|buoy]]s. The [[World Meteorological Organization]] acts to standardize the instrumentation, observing practices and timing of these observations worldwide. Stations either report hourly in [[METAR]] reports,<ref>[[National Climatic Data Center]]. [http://www.ncdc.noaa.gov/oa/climate/conversion/swometardecoder.html Key to METAR Surface Weather Observations.] Retrieved on [[2008-03-09]].</ref> or every six hours in [[SYNOP]] reports.<ref>[[UNISYS]]. [http://weather.unisys.com/wxp/Appendices/Formats/SYNOP.html SYNOP Data Format (FM-12): Surface Synoptic Observations.] Retrieved on [[2008-05-25]].</ref> Measurements of temperature, humidity and wind above the surface are found by launching [[radiosonde]]s on [[weather balloon]]s.<ref>[[NASA]]. [http://ghrc.msfc.nasa.gov:5721/dataset_documents/namsenegal_dataset.html NAMMA Senegal Radiosonde and Tower Flux.] Retrieved on [[2008-05-25]].</ref> Data are usually obtained from near the surface to the middle of the [[stratosphere]], about {{convert|21|km|abbr=on}}.<ref> Dian J. Gaffen. [http://www.aero.jussieu.fr/~sparc/News12/Radiosondes.html Radiosonde Observations and Their Use in SPARC-Related Investigations.] Retrieved on [[2008-05-25]].</ref> In recent years, data transmitted from commercial airplanes through the [[Aircraft Meteorological Data Relay]] (AMDAR) system has also been incorporated into upper air observation, primarily in numerical models.<ref>Bradley A Ballish and V. Krishna Kumar. [http://amdar.noaa.gov/docs/bams_ballish_kumar.pdf INVESTIGATION OF SYSTEMATIC DIFFERENCES IN AIRCRAFT AND RADIOSONDE TEMPERATURES WITH IMPLICATIONS FOR NWP AND CLIMATE STUDIES.] Retrieved on [[2008-05-25]].</ref> Increasingly, data from [[weather satellite]]s are being used because of their almost global coverage.<ref>[[NASA]]. [http://wwwghcc.msfc.nasa.gov/GOES/globalir.html Interactive Global Composite Weather Satellite Images.] Retrieved on [[2008-05-25]].</ref> 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 [[infrared]] (IR) data however can be used as it gives information on the temperature at the surface and cloud tops.<ref>[[NOAA]]. [http://www.goes.noaa.gov/ECIR4.html GOES Eastern US SECTOR Infrared Image.] Retrieved on [[2008-05-25]].</ref> 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. Both [[polar orbit]]ing and [[Geosynchronous satellite|geostationary satellites]] provide [[soundings]] of temperature and moisture throughout the depth of the atmosphere.<ref>[[Met Office]]. [http://www.metoffice.gov.uk/research/nwp/satellite/ Satellite applications.] Retrieved on [[2008-05-25]].</ref> Compared with similar data from radiosondes, the satellite data has the advantage of global coverage, however at a lower accuracy and resolution.<ref>Tony Reale. [http://cimss.ssec.wisc.edu/itwg/itsc/itsc12/presentations/1a4_T.Reale.ppt ATOVS Sounding Products (ITSVC-12).] Retrieved on [[2008-05-25]].</ref> [[Weather radar|Meteorological radar]] provide information on precipitation location and intensity, which can be used to estimate precipitation accumulations over time.<ref>Andrew Treloar and Peter Brookhouse. [http://www.csu.edu.au/special/bushfire99/papers/treloar/ The use of accumulated rainfall maps from weather radar systems to assist wildfire detection reconnaissance.] Retrieved on [[2008-05-25]].</ref> Additionally, if a [[Pulse-Doppler radar|Pulse Doppler]] [[weather radar]] is used then wind speed and direction can be determined.<ref>University of Washington. [http://www.artsci.washington.edu/news/WinterSpring03/Forecast.htm An improving forecast.] Retrieved on [[2007-04-15]].</ref> [[Image:2005-09-22-10PM CDT Hurricane Rita 3 day path.gif|right|thumb|Modern weather predictions aid in timely evacuations and potentially save lives and property damage]] ===Data assimilation and analysis=== 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. This is used to produce a three-dimensional representation of the temperature, moisture and wind called a meteorological analysis. This is the model's estimate of the current state of the atmosphere.<ref>[[UCAR]]. [http://www.mmm.ucar.edu/wrf/WG4/wrfvar/wrfvar-tutorial.htm The WRF Variational Data Assimilation System (WRF-Var).] Retrieved on [[2008-05-25]].</ref> ===Numerical weather prediction=== Numerical weather prediction models are [[computer simulation]]s of the atmosphere. They take the analysis as the starting point and evolve the state of the atmosphere forward in time using [[physics]] and [[fluid dynamics]]. The complicated equations which govern how the state of a [[fluid]] changes with time require [[supercomputer]]s to solve them. The output from the model provides the basis of the weather forecast.<ref>United Kingdom Met Office. [http://www.metoffice.gov.uk/research/nwp/index.html Numerical weather prediction.] Retrieved on [[2007-02-16]].</ref> ===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 [[bias]]es in the model, or of adjustment to take into account consensus among other numerical weather forecasts.<ref>Daniel Andersson. [http://www.diva-portal.org/his/abstract.xsql?dbid=312 Improved accuracy of surrogate models using output postprocessing.] Retrieved on [[2008-05-25]].</ref> 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. Here is an example of MOS Guidance for the Wilkes Barre/Scranton International Airport in Avoca, PA: MOS FORECASTS GFS MOS (MAV) KAVP GFS MOS GUIDANCE 7/14/2008 0600 UTC DT /JULY 14 /JULY 15 /JULY 16 / HR 12 15 18 21 00 03 06 09 12 15 18 21 00 03 06 09 12 15 18 00 06 X/N 84 59 88 56 92 TMP 66 74 81 81 75 68 64 61 65 75 84 86 78 67 61 57 63 80 88 83 67 DPT 63 62 58 57 59 59 58 57 58 57 54 52 54 54 53 52 54 57 55 59 60 CLD BK BK BK BK BK FW CL CL CL CL CL CL CL CL CL CL CL CL CL CL CL WDR 28 28 28 29 29 13 10 11 32 30 29 31 34 11 12 12 00 26 26 22 13 WSP 02 06 08 07 04 03 03 03 02 05 07 07 04 04 05 03 00 04 06 04 02 P06 4 0 4 5 1 0 2 6 0 4 4 P12 4 9 2 6 6 Q06 0 0 0 0 0 0 0 0 0 0 0 Q12 0 0 0 0 0 T06 0/ 0 4/11 1/ 6 0/ 0 0/ 0 3/11 1/ 5 1/ 0 3/ 0 6/ 6 T12 4/13 0/ 0 3/11 4/ 0 12/12 CIG 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 VIS 5 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 OBV BR N N N N N N N N N N N N N N N N N N N N Eta MOS (MET) KAVP ETA MOS GUIDANCE 7/14/2008 0000 UTC DT /JULY 14 /JULY 15 /JULY 16 / HR 06 09 12 15 18 21 00 03 06 09 12 15 18 21 00 03 06 09 12 18 00 X/N 82 58 82 55 86 TMP 67 65 67 74 80 80 75 67 62 60 64 72 79 81 73 64 59 56 61 83 78 DPT 65 62 62 59 56 56 58 59 58 57 59 58 54 52 55 54 53 53 55 56 60 CLD OV OV BK FW FW FW FW CL CL CL SC CL FW CL CL CL CL CL CL CL CL WDR 15 09 30 30 28 28 27 12 11 07 36 34 33 33 35 09 09 11 00 25 21 WSP 02 03 02 06 08 08 04 03 03 04 03 06 07 07 04 03 06 03 00 06 04 P06 19 6 2 4 8 4 1 1 8 4 2 P12 7 14 4 8 4 Q06 0 0 0 0 0 0 0 0 0 0 0 Q12 0 0 0 0 0 T06 4/ 0 0/ 1 6/ 9 0/ 4 2/ 0 1/ 0 7/ 6 2/ 2 0/ 0999/99 T12 5/ 1 6/10 4/ 0 7/ 6 999/99 CIG 3 7 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 VIS 4 5 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 OBV BR BR N N N N N N N N N N N N N N N N N N N GFSX MOS (MEX) KAVP GFSX MOS GUIDANCE 7/14/2008 0000 UTC FHR 24| 36 48| 60 72| 84 96|108 120|132 144|156 168|180 192 MON 14| TUE 15| WED 16| THU 17| FRI 18| SAT 19| SUN 20| MON 21 CLIMO X/N 84| 57 85| 56 91| 63 92| 65 92| 63 91| 65 83| 59 81 58 80 TMP 76| 64 77| 64 82| 70 84| 71 83| 70 82| 70 75| 65 73 DPT 57| 57 55| 54 57| 62 64| 64 63| 61 64| 64 61| 59 58 CLD CL| CL CL| CL CL| PC CL| PC CL| PC CL| CL CL| CL CL WND 7| 4 7| 6 6| 4 7| 4 12| 5 11| 5 8| 4 8 P12 6| 7 3| 7 6| 9 20| 11 11| 20 19| 20 16| 22 18 22 22 P24 | 12| 12| 20| 27| 32| 32| 32 36 Q12 0| 0 0| 0 0| 0 0| 0 0| 0 0| 0 | Q24 | 0| 0| 0| 0| 0| | T12 3| 1 2| 2 11| 6 20| 11 23| 10 23| 12 17| 9 21 T24 | 5 | 2 | 14 | 22 | 24 | 23 | 20 NGM MOS (FWC) AVP E NGM MOS GUIDANCE 7/14/08 1200 UTC DAY /JULY 14 /JULY 15 /JULY 16 / HOUR 18 21 00 03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 00 MN/MX 57 84 59 88 TEMP 76 79 75 67 62 59 63 74 81 83 78 68 63 60 65 78 85 86 81 DEWPT 59 57 57 58 57 55 56 58 55 54 56 58 57 56 58 61 60 60 62 CLDS SC SC SC CL CL CL CL CL SC SC CL CL CL CL CL CL SC SC SC WDIR 28 28 27 13 11 10 05 29 30 29 18 12 09 11 09 24 22 21 20 WSPD 07 08 05 03 02 02 01 03 03 04 02 02 05 04 01 03 05 07 06 POP06 4 1 1 0 0 0 0 4 8 POP12 2 0 0 9 QPF 0/ 0/ 0/0 0/ 0/0 0/ 0/0 0/ 0/0 TSV06 7/10 4/ 1 6/ 2 2/ 2 5/ 4 3/ 0 0/ 2 0/ 2 10/20 TSV12 11/10 7/ 3 6/ 4 0/ 4 CIG 7 7 7 7 7 7 7 7 7 7 7 7 7 VIS 5 5 5 5 5 5 5 5 5 5 5 5 5 OBVIS N N N N N N N N N N N N N Source for MOS Output is http://www.nws.noaa.gov/cgi-bin/mos/getall.pl?sta=KAVP ==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 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 weather forecasts|long range forecasts]].<ref>University of Illinois at Urbana-Champaign. [http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/fcst/mth/prst.rxml Persistence Forecasting: Today equals Tomorrow.] Retrieved on [[2007-02-16]].</ref> ===Use of a barometer=== Using barometric pressure and the pressure tendency (the change of pressure over time) has been used in forecasting since the late 19th century.<ref>[[USA Today]]. [http://www.usatoday.com/weather/wbarocx.htm Understanding air pressure.] Retrieved on [[2008-05-25]].</ref> The larger the change in pressure, especially if more than {{convert|3.5|hPa|inHg|lk=on|abbr=on}}, the larger the change in weather can be expected. If the pressure drop is rapid, a [[Low pressure area|low pressure system]] is approaching, and there is a greater chance of rain. [[High pressure area|Rapid pressure rises]] are associated with improving weather conditions, such as clearing skies.<ref>Weather Doctor. [http://www.islandnet.com/~see/weather/eyes/barometer3.htm Applying The Barometer To Weather Watching.] Retrieved on [[2008-05-25]].</ref> ===Looking at the sky=== [[Image:marestail.jpg|frame|right|Marestail shows moisture at high altitude, signalling the later arrival of wet weather.]] Along with pressure tendency, use of the sky condition is one of more important weather parameters that can be 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. Morning [[fog]] portends fair conditions, as rainy conditions are preceded by wind or clouds which prevent fog formation. The approach of a line of [[thunderstorm]]s could indicate the approach of a [[cold front]]. Cloud-free skies are indicative of fair weather for the near future.<ref>Mark Moore. [http://www.nwac.us/education_resources/Field_forecasting.pdf Field Forecasting - A Short Summary.] Retrieved on [[2008-05-25]].</ref> The use of sky cover in weather prediction has led to various weather lore over the centuries.<ref>Jerry Wilson. [http://wilstar.com/skywatch.htm#indicators Skywatch: Signs of the Weather.] Retrieved on [[2008-05-25]].</ref> ===Nowcasting=== The forecasting of the weather within the next six hours is often referred to as '''nowcasting'''.<ref>Glossary of Meteorology. [http://amsglossary.allenpress.com/glossary/search?p=1&query=nowcast&submit=Search Nowcast.] Retrieved on [[2008-05-25]].</ref> 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.<ref>E-notes.com. [http://science.enotes.com/science-fact-finder/weather-climate/what-nowcasting Weather and Climate | What Is Nowcasting?] Retrieved on [[2007-02-16]].</ref> ===Use of forecast models=== [[Image:NAM 500 MB.PNG|right|250px|thumb|An example of 500 [[millibar|mbar]] [[geopotential height]] prediction from a numerical weather prediction model]] In the past, the human forecaster was responsible for generating the entire weather forecast based upon available observations.<ref>[[NASA]]. [http://earthobservatory.nasa.gov/Library/WxForecasting/wx2.html Weather Forecasting Through the Ages.] Retrieved on [[2008-05-25]].</ref> Today, human input is generally confined to choosing a model based on various parameters, such as model biases and performance.<ref name="Klaus">Klaus Weickmann, Jeff Whitaker, Andres Roubicek and Catherine Smith. [http://www.cdc.noaa.gov/spotlight/12012001/ The Use of Ensemble Forecasts to Produce Improved Medium Range (3-15 days) Weather Forecasts.] Retrieved on [[2007-02-16]].</ref> Using a consensus of forecast models, as well as ensemble members of the various models, can help reduce forecast error.<ref name="TBK">Todd Kimberlain. [http://www.hpc.ncep.noaa.gov/research/TropicalTalk.ppt Tropical cyclone motion and intensity talk (June 2007).] Retrieved on [[2007-07-21]].</ref> However, regardless how small the average error becomes with any individual system, large errors within any particularly piece of guidance are still possible on any given model run.<ref>Richard J. Pasch, Mike Fiorino, and [[Chris Landsea]]. [http://www.emc.ncep.noaa.gov/research/NCEP-EMCModelReview2006/TPC-NCEP2006.ppt TPC/NHC’S REVIEW OF THE NCEP PRODUCTION SUITE FOR 2006.] Retrieved on [[2008-05-05]].</ref> 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 which 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.<ref>Roebber P. J. and Bosart L. F. [http://cat.inist.fr/?aModele=afficheN&cpsidt=2512901 The complex relationship between forecast skill and forecast value : A real-world analysis.] Retrieved on [[2008-05-25]].</ref> ===Analog technique=== The Analog technique is a complex way of making a forecast, requiring the forecaster to remember 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.<ref>[http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/fcst/mth/oth.rxml Other Forecasting Methods: climatology, analogue and numerical weather prediction.] Retrieved on [[2006-02-16]].</ref> Some call this type of forecasting pattern recognition. It remains a useful method of observing rainfall over data voids such as oceans,<ref>Kenneth C. Allen. [http://stinet.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADP006190 Pattern Recognition Techniques Applied to the NASA-ACTS Order-Wire Problem.] Retrieved on [[2007-02-16]].</ref> 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.<Ref>Weather Associates, Inc. [http://www.weatherassociates.com/courses.htm The Role of Teleconnections & Ensemble Forecasting in Extended- to Medium-Range Forecasting.] Retrieved on [[2007-02-16]].</ref> An example of teleconnections are by using [[El Niño-Southern Oscillation]] (ENSO) related phenomena.<ref>Thinkquest.org. [http://library.thinkquest.org/20901/teleconnections.htm Teleconnections: Linking El Niño with Other Places.] Retrieved on [[2007-02-16]].</ref> ===Ensemble forecasting=== Although a forecast model will predict 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 and the inexactness of the initial observations. 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 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]] entails the production of many forecasts in order 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. Ensemble forecasts are increasingly being used for operational weather forecasting (for example at [[European Centre for Medium-Range Weather Forecasts]] (ECMWF), [[National Centers for Environmental Prediction]] (NCEP), and the Canadian forecasting center). <ref name="Klaus">Klaus Weickmann, Jeff Whitaker, Andres Roubicek and Catherine Smith. [http://www.cdc.noaa.gov/spotlight/12012001/ The Use of Ensemble Forecasts to Produce Improved Medium Range (3-15 days) Weather Forecasts.] Retrieved on [[2007-02-16]].</ref> ==Public uses== [[Image:Newspaper weather forecast - today and tomorrow.svg|frame|thumb|right|An example of a two-day weather forecast in the [[Visual language|visual style]] that an [[United States|American]] [[newspaper]] might use.]] Most end users of forecasts are members of the general public. Thunderstorms can create strong winds and dangerous [[lightning]] strikes that can lead to deaths, power outages,<ref>University of Illinois at Urbana-Champaign. [http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/svr/dngr/light.rxml Lightning.] Retrieved on [[2007-02-16]].</ref> and widespread hail damage. Heavy snow or rain can bring transportation and commerce to a stand-still,<ref>[[Associated Press]]. [http://www.msnbc.msn.com/id/17063535/ Upstate N.Y. residents dig out from heavy snow.] Retrieved on [[2008-05-25]].</ref> as well as cause [[flood]]ing in low-lying areas.<ref>National Flood Insurance Program. [http://en.wikipedia.org/w/index.php?title=Weather_forecasting&action=edit&section=13 Flood Risk Scenarios: Flash Flood.] Retrieved on [[2008-05-25]].</ref> Excessive [[Heat wave|heat]] or [[cold wave]]s can sicken or kill those with inadequate utilities, and [[drought]]s can impact water usage and destroy vegetation. Several countries employ government agencies to provide forecasts and watches/warnings/advisories to the public in order 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]]'s [[National Weather Service]] (NWS)<ref>National Weather Service. [http://www.nws.noaa.gov/admin.php About NOAA's National Weather Service.] Retrieved on [[2007-02-16]].</ref> and [[Environment Canada]]'s [[Meteorological Service of Canada|Meteorological Service]] (MSC).<ref>Environment Canada. [http://www.weatheroffice.ec.gc.ca/canada_e.html Main website.] Retrieved on [[2007-02-16]].</ref> Traditionally, [[newspaper]], [[television]], and [[radio]] have been the primary outlets for presenting weather forecast information to the public. Increasingly, the internet is being used due to the vast amount of specific information that can be found.<ref>Canadian Heritage. [http://www.canadianheritage.gc.ca/progs/ac-ca/progs/ri-bpi/pubs/2005_02/4_e.cfm Primary Sources of Local Information.] Retrieved on [[2008-05-26]].</ref> 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 which the national weather services issue in the case that severe or hazardous weather is expected. This is done to protect life and property.<ref>[[National Weather Service]]. [http://www.weather.gov/mission.shtml National Weather Service Mission Statement.] Retrieved on [[2008-05-25]].</ref> Some of the most commonly known of severe weather advisories are 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 cyclone]], and fog.<ref>[[Environment Canada]]. [http://www.msc-smc.ec.gc.ca/cd/brochures/warning_e.cfm? Canadian Weather Alerts.] Retrieved on [[2008-05-26]].</ref> 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.<ref>[[Federal Communications Commission]]. [http://www.fcc.gov/pshs/services/eas/ Emergency Alert System.] Retrieved on [[2008-05-26]].</ref> === Air traffic === [[Image:Plume from eruption of Chaiten volcano, Chile.jpg|thumb|right|Ash cloud from the 2008 eruption of [[Chaitén (volcano)|Chaitén volcano]] streching across [[Patagonia]] from the Pacific to the Atlantic Ocean]] {{seealso|Terminal Aerodrome Forecast}} 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.<ref>[[Government Printing Office]]. [http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr;sid=199eb678c4c22b4202e5809c99045c7c;rgn=div7;view=text;node=14%3A2.0.1.3.10.2.5;idno=14;cc=ecfr Title 14: Aeronautics and Space.] Retrieved on [[2008-05-26]].</ref> [[Turbulence]] and [[Atmospheric icing|icing]] are also significant in-flight hazards.<ref>Aircraft Owners and Pilots Association. [http://www.aopa.org/asf/publications/sa11.pdf Aircraft Icing.] Retrieved on [[2008-05-26]].</ref> Thunderstorms are a problem for all aircraft because of severe turbulence due to their [[Vertical draft|updrafts]] and [[Outflow boundary|outflow boundaries]],<ref>[[National Weather Service]] Forecast Office Dodge City, Kansas. [http://www.crh.noaa.gov/ddc/research/bore/HPCtalk.ppt Aviation Hazards They Didn’t Tell You About.] Retrieved on [[2008-05-26]].</ref> 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.<ref>[[Bureau of Meteorology]]. [http://www.caem.wmo.int/_pdf/thunderstorms/thunderstorms_02_effects.pdf Aviation Hazards: Thunderstorms and Deep Convection.] Retrieved on [[2008-05-26]].</ref> [[Volcanic ash]] is also a significant problem for aviation, as aircraft can lose engine power within ash clouds.<ref>[http://www.usgs.gov/tech-transfer/factsheets/7.html Volcanic Ash Aviation Hazard.] Retrieved on [[2008-05-26]].</ref> On a day to day basis airliners are routed to take advantage of the [[jet stream]] tailwind to improve fuel efficiency.<ref>Ned Rozell. [http://www.gi.alaska.edu/ScienceForum/ASF17/1727.html Amazing flying machines allow time travel.] Retrieved on [[2008-05-08]].</ref> Aircrews are briefed prior to [[takeoff]] on the conditions to expect en route and at their destination.<ref>[[National Weather Service]]. [http://www.weather.gov/om/brochures/pilot.htm A Pilot's Guide to Aviation Weather Services.] Retrieved on [[2008-05-26]].</ref> Additionally, airports often change which [[runway]] is being used to take advantage of a [[headwind]]. This reduces the distance required for takeoff, and to eliminates potential [[crosswind]]s.<ref>Eric C. King. [http://takeofftools.com/Documents/Crosswind%20Calculator%20Instructions.pdf Takeoff Tools Crosswind Calculator Instructions.] Retrieved on [[2008-05-26]].</ref> ===Marine=== Commercial and recreational use of waterways can be limited significantly by wind direction and speed, [[Ocean surface wave|wave]] 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).<ref>Great Lakes and Seaway Shipping. [http://www.boatnerd.com/facts-figures/mafor.htm MAFOR Weather Code.] Retrieved on [[2008-05-27]].</ref> ===Agriculture=== [[Farmer]]s 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]],<ref>Blair Fannin. [http://southwestfarmpress.com/news/061406-Texas-weather/ Dry weather conditions continue for Texas.] Retrieved on [[2008-05-26]].</ref> and [[Maize|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]].<ref>Dr. Terry Mader. [http://beef.unl.edu/stories/200004030.shtml Drought Corn Silage.] Retrieved on [[2008-05-26]].</ref> [[Frost]]s and freezes play havoc with crops both during the spring and fall. For example, [[peach]] trees in full bloom can have their potential peach crop decimated by a spring freeze.<ref>Kathryn C. Taylor. [http://pubs.caes.uga.edu/caespubs/pubcd/C877.htm Peach Orchard Establishment and Young Tree Care.] Retrieved on [[2008-05-26]].</ref> [[Orange (fruit)|Orange]] groves can suffer significant damage during frosts and freezes, regardless of their timing.<ref>[[Associated Press]]. [http://query.nytimes.com/gst/fullpage.html?res=9D0CE5DB1E30F937A25752C0A967958260 After Freeze, Counting Losses to Orange Crop.] Retrieved on [[2008-05-26]].</ref> ===Utility companies=== [[Image:Air handling unit.JPG|thumb|right|An [[air handling unit]] is used for the heating and cooling of air in a central location (click on image for legend).]] {{Main article|Degree day}} 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 {{convert|65|F|C}}. Cooler temperatures force heating degree days (one per degree Fahrenheit), while warmer temperatures force cooling degree days.<ref>[[Climate Prediction Center]]. [http://www.cpc.noaa.gov/products/analysis_monitoring/cdus/degree_days/ddayexp.shtml Degree Day Explanation.] Retrieved on [[2008-05-25]].</ref> In winter, severe cold weather can cause a surge in demand as people turn up their heating.<ref>[[The New York Times]]. [http://query.nytimes.com/gst/fullpage.html?res=9F0CE7D9123AF935A15751C0A965958260 FUTURES/OPTIONS; Cold Weather Brings Surge In Prices of Heating Fuels.] Retrieved on [[2008-05-25]].</ref> Similarly, in summer a surge in demand can be linked with the increased use of [[air conditioning]] systems in hot weather.<ref>[[BBC]]. [http://news.bbc.co.uk/1/hi/uk/5212724.stm Heatwave causes electricity surge.] Retrieved on [[2008-05-25]].</ref> 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 [[Power outage|brownout]]s and blackouts.<ref>Toronto Catholic Schools. [http://www.tcdsb.org/environment/energydrill/EDSP_KeyMessages_FINAL.pdf The Seven Key Messages of the Energy Drill Program.] Retrieved on [[2008-05-25]].</ref> ===Private sector=== Increasingly, private companies pay for weather forecasts tailored to their needs so that they can increase their profits or avoid large losses.<ref>CSIRO. [http://www.csiro.au/science/pps9c.html#1 Providing specialized weather forecasts.] Retrieved on [[2008-05-25]].</ref> 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.<ref>Stephen Jewson and Rodrigo Caballero. [http://search.ssrn.com/sol3/papers.cfm?abstract_id=405780 The Use of Weather Forecasts in the Pricing of Weather Derivatives.] Retrieved on [[2008-05-25]].</ref> ===Military applications=== [[Image:Npmoc.gif|thumb|right]] Similarly 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. The [[United States Navy]] provides a special service to both themselves and the rest of the federal government by issuing forecasts for tropical cyclone across the [[Pacific Ocean|Pacific]] and [[Indian Ocean]]s through their [[Joint Typhoon Warning Center]].<ref>[[Joint Typhoon Warning Center]]. [http://metocph.nmci.navy.mil/jtwc/menu/JTWC_mission.html Joint Typhoon Warning Center Mission Statement.] Retrieved on [[2008-05-27]].</ref> ====United States==== Within the [[United States]], 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; [[United States Air Force|Air Force]] forecasters cover air operations in both wartime and peacetime operations and provide [[United States Army|Army]] support;<ref>[[United States Air Force]].[http://www.af.mil/factsheets/factsheet.asp?fsID=157 Air Force Weather Agency.] Retrieved on [[2008-05-26]].</ref> [[United States Coast Guard]] marine science technicians provide ship forecasts for ice breakers and other various operations within their realm;<ref>[[United States Military]]. [http://www.usmilitary.com/coastguardenlistedoccupations.html#engineeringscienceandtechnical US Coast Guard Jobs - Enlisted Occupations.] Retrieved on [[2008-05-26]].</ref> and Marine forecasters provide support for ground- and air-based [[United States Marine Corps]] operations.<ref>Rod Powers. [http://usmilitary.about.com/od/enlistedjo2/a/68.htm United States Marine Corps Enlisted Job Descriptions and Qualification Factors: FIELD 68 - METEOROLOGY AND OCEANOGRAPHY (METOC).] Retrieved on [[2008-05-26]].</ref> All four military branches take their initial meteorology training at [[Keesler Air Force Base]].<ref>[[Keesler Air Force Base]]. [http://www.keesler.af.mil/shared/media/document/AFD-061113-086.pdf Keesler News: March 9, 2006.] Retrieved on [[2008-05-26]].</ref> Military and civilian forecasters actively cooperate in analyzing, creating and critiquing weather forecast products. ==References== {{reflist|2}} ==External links== <!--==========================({{NoMoreLinks}})============================ | PLEASE BE CAUTIOUS IN ADDING MORE LINKS TO THIS ARTICLE. WIKIPEDIA | | IS NOT A COLLECTION OF LINKS NOR SHOULD IT BE USED FOR ADVERTISING. | | | | Excessive or inappropriate links WILL BE DELETED. | | See [[Wikipedia:External links]] & [[Wikipedia:Spam]] for details. | | | | If there are already plentiful links, please propose additions or | | replacements on this article's discussion page. Or submit your link | | to the relevant category at the Open Directory Project (dmoz.org) | | and link back to that category using the {{dmoz}} template. | =========================({{NoMoreLinks}})=============================--> ===Meteorological agencies=== These are academic or governmental meteorology organizations. Most provide at least a limited forecast for their area of interest on their website. *[http://www.wmo.int The World Meteorological Organization] *[http://www.ecmwf.int/ European Centre for Medium Range Weather Forecasting (ECMWF)] *[http://www.bom.gov.au Australian Bureau of Meteorology] *[http://www.meteo.be/ Royal Meteorological Institute of Belgium] *[http://weatheroffice.ec.gc.ca/canada_e.html Environment Canada Weather Office] *[http://www.fmi.fi/en/index.html Finnish Meteorological Institute] *[http://www.meteofrance.com/FR/index.jsp French National Meteorological Service] *[http://www.meteo.gov.gr The Hellenic National Meteorological Service (Greece)] *[http://www.hko.gov.hk/ Hong Kong Observatory] *[http://www.met.ie/ Met Éireann (Ireland)] *[http://www.meteoam.it/ Italian Air Force (Aeronautica Militare) Meteorological Service] *[http://web.kma.go.kr/eng/index.jsp Korea Meteorological Administration] *[http://www.metservice.com New Zealand MetService] *[http://www.un.org/peace/africa/Diamond.html South African Weather Service] *[http://www.meteoswiss.ch/en/index.shtml Meteo Suisse (Swiss Weather Agency, in English] *[http://www.metoffice.gov.uk/ The Met Office of the UK] *[http://www.noaa.gov/wx.html United States NOAA weather page] ===Other external links=== *[http://eh.net/encyclopedia/article/craft.weather.forcasting.history Economic history and impact of weather forecasting] from EH.NET ==See also== {| |- valign=top | * [[List of meteorology institutions]] * [[Citizen Weather Observer Program]] * [[Downscaling]] * [[Environment Canada]] * [[Forecasting]] * [[geodesic grid]] * [[Meteorology]] | * [[National Collegiate Weather Forecasting Contest]] * [[Space Weather Prediction Center]] (SPWC) * [[Trend estimation]] * [[Tropical cyclone forecasting]] * [[Weather control]] * [[Weather wars]] * [[WxChallenge]] |} {{Meteorological variables}} {{Meteorological equipment}} {{Earth-based meteorological observation}} {{Space-based meteorological observation}} [[Category:Broadcasting]] [[Category:Weather prediction| ]] [[cs:Předpověď počasí]] [[da:Vejrudsigt]] [[de:Wettervorhersage]] [[fr:Prévision météorologique]] [[ko:일기 예보]] [[id:Ramalan cuaca]] [[he:חיזוי מזג אוויר]] [[nl:Weerbericht]] [[ja:天気予報]] [[no:Værvarsling]] [[nn:Vêrvarsling]] [[pl:Prognoza pogody]] [[pt:Previsão do tempo]] [[ru:Прогноз погоды]] [[fi:Sään ennustaminen]] [[uk:Прогноз погоди]] [[zh:天气预报]]