Editing Weather (section)

== Forecasting ==
{{Main|Weather forecasting}}
[[Image:Day5pressureforecast.png|thumb|right|Forecast of surface pressures five days into the future for the north Pacific, North America, and the north Atlantic Ocean as on 9 June 2008]]

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.<ref>Eric D. Craft. [http://eh.net/encyclopedia/article/craft.weather.forcasting.history ''An Economic History of Weather Forecasting''.] {{webarchive|url=https://web.archive.org/web/20070503193324/http://eh.net/encyclopedia/article/craft.weather.forcasting.history |date=3 May 2007 }} Retrieved on 15 April 2007.</ref> 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.<ref>[[NASA]]. [http://earthobservatory.nasa.gov/Library/WxForecasting/wx2.html Weather Forecasting Through the Ages.] {{Webarchive|url=https://web.archive.org/web/20050910210732/http://earthobservatory.nasa.gov/Library/WxForecasting/wx2.html |date=10 September 2005 }} Retrieved on 25 May 2008.</ref>

Once an all-human endeavor based mainly upon changes in [[Atmospheric pressure|barometric pressure]], current weather conditions, and sky condition,<ref>Weather Doctor. [http://www.islandnet.com/~see/weather/eyes/barometer3.htm Applying The Barometer To Weather Watching.] {{Webarchive|url=https://web.archive.org/web/20080509105153/http://www.islandnet.com/~see/weather/eyes/barometer3.htm |date=9 May 2008 }} Retrieved on 25 May 2008.</ref><ref>Mark Moore. [http://www.nwac.us/education_resources/Field_forecasting.pdf Field Forecasting: A Short Summary.] {{webarchive|url=https://web.archive.org/web/20090325034756/http://www.nwac.us/education_resources/Field_forecasting.pdf |date=25 March 2009 }} Retrieved on 25 May 2008.</ref> [[numerical weather prediction|forecast models]] are now used to determine future conditions. On the other hand, human input is still required to pick the best possible forecast model to base the forecast upon, which involves many disciplines such as 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, the error involved in measuring the initial conditions, and an incomplete understanding of atmospheric processes mean that forecasts become less accurate as of 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 helps to narrow the error and pick the most likely outcome.<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.] {{Webarchive|url=https://web.archive.org/web/20071215055130/http://www.cdc.noaa.gov/spotlight/12012001/ |date=15 December 2007 }} Retrieved on 16 February 2007.</ref><ref name="TBK">Todd Kimberlain. [http://www.wpc.ncep.noaa.gov/research/TropicalTalk.ppt Tropical cyclone motion and intensity talk (June 2007).] {{Webarchive|url=https://web.archive.org/web/20210227154914/http://www.wpc.ncep.noaa.gov/research/TropicalTalk.ppt |date=27 February 2021 }} Retrieved on 21 July 2007.</ref><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.]{{dead link|date=January 2018 |bot=InternetArchiveBot |fix-attempted=yes }} Retrieved on 5 May 2008.</ref>

There are a variety of end users to weather forecasts. Weather warnings are important forecasts because they are used to protect life and property.<ref>[[National Weather Service]]. [http://www.weather.gov/mission.shtml National Weather Service Mission Statement.] {{webarchive|url=https://web.archive.org/web/20131124214601/http://www.weather.gov/mission.shtml |date=24 November 2013 }} Retrieved on 25 May 2008.</ref><ref>{{Cite web |url=http://www.meteo.si/met/en/app/webmet/#webmet==8Sdwx2bhR2cv0WZ0V2bvEGcw9ydlJWblR3LwVnaz9Ccy92ZvIXZhxWbvkWbhdWZvA3bp5GdugXbsxXZ1J3bwVGfp1WYnVGf7R2btFWaupzJzx2b2VmbpF2JsAXYyFWblRXZypzJTFEVFxETJRVRfxUQUV0UUdSf; |title=National Meteorological Service of Slovenia |access-date=25 February 2012 |archive-url=https://web.archive.org/web/20120618145647/http://www.meteo.si/met/en/app/webmet/#webmet==8Sdwx2bhR2cv0WZ0V2bvEGcw9ydlJWblR3LwVnaz9Ccy92ZvIXZhxWbvkWbhdWZvA3bp5GdugXbsxXZ1J3bwVGfp1WYnVGf7R2btFWaupzJzx2b2VmbpF2JsAXYyFWblRXZypzJTFEVFxETJRVRfxUQUV0UUdSf; |archive-date=18 June 2012 |url-status=dead }}</ref> Forecasts based on temperature and [[Precipitation (meteorology)|precipitation]] are important to agriculture,<ref>Blair Fannin. [http://southwestfarmpress.com/news/061406-Texas-weather/ Dry weather conditions continue for Texas.] {{webarchive|url=https://web.archive.org/web/20090703095038/http://southwestfarmpress.com/news/061406-Texas-weather/ |date=3 July 2009 }} Retrieved on 26 May 2008.</ref><ref>Dr. Terry Mader. [http://beef.unl.edu/stories/200004030.shtml Drought Corn Silage.] {{webarchive|url=https://web.archive.org/web/20111005203246/http://beef.unl.edu/stories/200004030.shtml |date=5 October 2011 }} Retrieved on 26 May 2008.</ref><ref>Kathryn C. Taylor. [http://pubs.caes.uga.edu/caespubs/pubcd/C877.htm Peach Orchard Establishment and Young Tree Care.] {{webarchive|url=https://web.archive.org/web/20081224112403/http://pubs.caes.uga.edu/caespubs/pubcd/C877.htm |date=24 December 2008 }} Retrieved on 26 May 2008.</ref><ref>[[Associated Press]]. [https://query.nytimes.com/gst/fullpage.html?res=9D0CE5DB1E30F937A25752C0A967958260  After Freeze, Counting Losses to Orange Crop.] {{Webarchive|url=https://web.archive.org/web/20210331130921/https://www.nytimes.com/1991/01/14/us/after-freeze-counting-losses-to-orange-crop.html |date=31 March 2021 }} Retrieved on 26 May 2008.</ref> and therefore to commodity traders within stock markets. Temperature forecasts are used by utility companies to estimate demand over coming days.<ref>[[The New York Times]]. [https://query.nytimes.com/gst/fullpage.html?res=9F0CE7D9123AF935A15751C0A965958260  Futures/Options; Cold Weather Brings Surge In Prices of Heating Fuels.] {{Webarchive|url=https://web.archive.org/web/20231214135805/https://www.nytimes.com/1993/02/26/business/futures-options-cold-weather-brings-surge-in-prices-of-heating-fuels.html |date=14 December 2023 }} Retrieved on 25 May 2008.</ref><ref>[[BBC]]. [http://news.bbc.co.uk/1/hi/uk/5212724.stm Heatwave causes electricity surge.] {{Webarchive|url=https://web.archive.org/web/20090520060913/http://news.bbc.co.uk/1/hi/uk/5212724.stm |date=20 May 2009 }} Retrieved on 25 May 2008.</ref><ref>Toronto Catholic Schools. [http://www.tcdsb.org/environment/energydrill/EDSP_KeyMessages_FINAL.pdf The Seven Key Messages of the Energy Drill Program.] {{webarchive|url=https://web.archive.org/web/20120217042744/http://www.tcdsb.org/environment/energydrill/EDSP_KeyMessages_FINAL.pdf |date=17 February 2012 }} Retrieved on 25 May 2008.</ref>

In some areas, 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 to survive through them.

Tropical weather forecasting is different from that at higher latitudes. The sun shines more directly on the tropics than on higher latitudes (at least on average over a year), which makes the tropics warm (Stevens 2011). And, the vertical direction (up, as one stands on the Earth's surface) is perpendicular to the Earth's axis of rotation at the equator, while the axis of rotation and the vertical are the same at the pole; this causes the Earth's rotation to influence the atmospheric circulation more strongly at high latitudes than low latitudes. Because of these two factors, clouds and rainstorms in the tropics can occur more spontaneously compared to those at higher latitudes, where they are more tightly controlled by larger-scale forces in the atmosphere. Because of these differences, clouds and rain are more difficult to forecast in the tropics than at higher latitudes. On the other hand, the temperature is easily forecast in the tropics, because it does not change much.<ref>{{Cite web|url=https://www.nature.com/scitable/knowledge/library/tropical-weather-84224797/|title=Tropical Weather {{!}} Learn Science at Scitable|website=nature.com|access-date=2020-02-08|archive-date=8 September 2020|archive-url=https://web.archive.org/web/20200908161720/https://www.nature.com/scitable/knowledge/library/tropical-weather-84224797/|url-status=live}}</ref>