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The study argues that forecast “goodness” should be judged mainly by the probabilistic reliability of ensemble-based predictions, reserving the highest rating for systems that remain reliable while showing small ensemble spread as a trustworthy indicator of low error. The paper examines regional temperature and precipitation reliability for ECMWF’s operational system and discusses prospects for achieving top performance globally.",{"@graph":69,"@context":122},[70,84,105],{"@type":71,"itemListElement":72},"BreadcrumbList",[73,77,79,82],{"item":74,"name":75,"@type":76,"position":8},"https://docshare.wps.com","Home","ListItem",{"item":78,"name":9,"@type":76,"position":14},"https://docshare.wps.com/document/",{"item":80,"name":40,"@type":76,"position":81},"https://docshare.wps.com/document/research-report/",3,{"item":83,"name":65,"@type":76,"position":19},"https://docshare.wps.com/document/on-the-reliability-of-seasonal-climate-forecasts/665608/",{"url":83,"name":65,"@type":85,"image":86,"author":91,"headline":65,"publisher":94,"fileFormat":97,"inLanguage":63,"description":67,"dateModified":98,"datePublished":99,"encodingFormat":97,"isAccessibleForFree":100,"interactionStatistic":101},"DigitalDocument",{"url":87,"@type":88,"width":89,"height":90},"https://docshare.wps.com/thumbnails/on-the-reliability-of-seasonal-climate-forecasts/665608.png","ImageObject",300,407,{"name":92,"@type":93},"Hazel","Person",{"url":74,"name":95,"@type":96},"DocShare","Organization","application/pdf","2026-10-30","2026-10-29",true,{"@type":102,"interactionType":103,"userInteractionCount":14},"InteractionCounter",{"@type":104},"ViewAction",{"@type":106,"mainEntity":107},"FAQPage",[108,114,118],{"name":109,"@type":110,"acceptedAnswer":111},"Why can seasonal climate forecasts be treated as probabilistic rather than deterministic?","Question",{"text":112,"@type":113},"Seasonal predictions target seasonal-mean statistics rather than detailed day-to-day evolution because the climate system is chaotic. Coupled ocean-atmosphere models are also approximate representations, so deterministic forecasts would be unreliable and untrustworthy.","Answer",{"name":115,"@type":110,"acceptedAnswer":116},"What does the paper mean by “reliable” probabilistic forecasting?",{"text":117,"@type":113},"A forecast is reliable when it shows statistical reliability: when the system predicts a given probability (e.g., 80% chance of above-average rainfall), the observed outcomes match that probability in about the expected proportion of cases.",{"name":119,"@type":110,"acceptedAnswer":120},"How is the quality of seasonal forecasts assessed on the 1–5 scale?",{"text":121,"@type":113},"The paper proposes that “goodness” should be assessed primarily through the probabilistic reliability of ensemble-based forecasts. The highest rating should be reserved for systems that are not only reliable overall, but also where small ensemble spread reliably indicates low forecast error.","https://schema.org",{"og:url":83,"og:type":124,"og:title":65,"og:site_name":95,"og:description":67},"article",{"robots":126,"canonical":83},"index,follow",{"doc_id":128,"site_id":62},665608,1793305164,{"code":4,"msg":5,"data":131},{"doc_id":128,"user_id":132,"nickname":92,"user_avatar":133,"doc_module":4,"category_id":39,"category_name":40,"doc_title":65,"doc_description":67,"doc_content":134,"file_id":135,"file_url":136,"file_type":137,"file_size":138,"view_count":14,"is_deleted":4,"is_public":8,"is_downloadable":8,"audit_status":8,"page_count":139,"language":140,"language_code":63,"site_id":62,"html_lang":63,"table_of_contents":141,"faqs":142,"seo_title":143,"seo_description":67,"update_tm":129,"read_time":144},137441390410,"https://ap-avatar.wpscdn.com/avatar/2000252f4ab5702993?_k=1776741390130283984","On the Reliability of Seasonal Climate  \nForecasts  \nby  \nA. Weisheimer and T. N. Palmer  \nNational Centre for Atmospheric Science (NCAS), Department of Physics,  \nUniversity of Oxford, UK  \nand  \nEuropean Centre for MediumHRange Weather Forecasts (ECMWF), Reading, UK  \nAbstract  \nSeasonal climate forecasts are being used increasingly across a range of application sectors. A recent UK governmental report asked: How good are seasonal climate forecasts on a scale of 1H5 (where 5 is very good), and how good can we expect them to be in 30 years time? Seasonal climate forecasts are made from ensembles of integrations of numerical models of climate. We argue that“goodness” should be assessed primarily in terms of the probabilistic reliability of these ensembleHbased forecasts and that a `5’ should be reserved for systems which are not only reliable overall, but where, in particular, small ensemble spread is a reliable indicator of low ensemble forecast error. We study the reliability of regional temperature and precipitation forecasts of the current operational seasonal forecast system of the European Centre for MediumHRange Weather Forecasts, universally regarded as a world leading operational institute producing seasonal climate forecasts. A wide range of “goodness” rankings, depending on region and variable (with summer forecasts of rainfall over Northern Europe performing exceptionally poorly) is found. Finally, we discuss the prospects of reaching “5” across all regions and variables in 30 years time.  \n1. Introduction  \nOver the last 30 years, the science of predicting seasonal timescale fluctuations in weather has grown from a research activity undertaken in a few academic and research institutes (eg Cane et al, 1986), to a routine operational activity in a number of meteorological forecast services (Arribas et al., 2011; Stockdale et al., 2011; Saha et al., 2013) . Unlike conventional weather forecasts, seasonal predictions do not attempt to forecast the detailed dayHtoHday evolution of weather. Such detailed prediction is ruled out by the chaotic nature of the climate system, otherwise known as the “Butterfly Effect”(Lorenz, 1963) . Rather, seasonal predictions provide estimates of seasonalHmean statistics of weather, typically up to three months ahead of the season in question. Hence, for example, a seasonal forecast can provide information on how likely it is that the coming season will be wetter, drier, warmer, or colder than normal. The physical basis for such estimates arises from the effect of predictable seasonalHtimescale signals arising from the ocean, and to a lesser extent the land surface, on the atmosphere (Palmer and Anderson, 1994) . The key paradigm for seasonal forecasting is El Niño, a coupled oceanHatmosphere phenomenon occurring primarily in the tropical Pacific and predictable six months and more ahead (Jin et al., 2008; Weisheimer et al., 2009) .  \nSuch information is relevant to a variety of users in weatherHsensitive sectors, and therefore can influence decisions made in these sectors. As a result, seasonal climate forecasts are increasingly being used across a range of application areas; see Dessai and Soares (2013) for a recent review. For example, information about seasonal average rainfall and temperature for the growing season can potentially influence a farmer’s decision about which crops to plant ahead of time, or a humanitarian organisation’s strategy for anticipating food shortages in droughtH prone regions of the developing world. However, this information is only useful if it is skilful.  \nIn the literature there exists a plethora of methods to estimate the skill of forecasts (Jolliffe and Stephenson, 2011) . In general, each of these methods quantifies a different detailed aspect of the forecast quality. In this paper, however, we try to simplify the question. Rather than coming up with complex estimates of different characteristics of forecast skill whose relevance strongly depends on th","cbCaib2tRm2TUqhi","https://ap.wps.com/l/cbCaib2tRm2TUqhi","pdf",1555555,21,"English","# Abstract\n# Introduction\n## Seasonal prediction purpose and limits\n## Reliability and probabilistic interpretation","[{\"question\":\"Why can seasonal climate forecasts be treated as probabilistic rather than deterministic?\",\"answer\":\"Seasonal predictions target seasonal-mean statistics rather than detailed day-to-day evolution because the climate system is chaotic. Coupled ocean-atmosphere models are also approximate representations, so deterministic forecasts would be unreliable and untrustworthy.\"},{\"question\":\"What does the paper mean by “reliable” probabilistic forecasting?\",\"answer\":\"A forecast is reliable when it shows statistical reliability: when the system predicts a given probability (e.g., 80% chance of above-average rainfall), the observed outcomes match that probability in about the expected proportion of cases.\"},{\"question\":\"How is the quality of seasonal forecasts assessed on the 1–5 scale?\",\"answer\":\"The paper proposes that “goodness” should be assessed primarily through the probabilistic reliability of ensemble-based forecasts. The highest rating should be reserved for systems that are not only reliable overall, but also where small ensemble spread reliably indicates low forecast error.\"}]","On the Reliability of Seasonal Climate Forecasts | PDF",53]