Current and Emerging Developments in Subseasonal to Decadal Prediction
Authors: Merryfield William J. , Baehr Johanna , Batté Lauriane , Becker Emily J. , Butler Amy H. , Coelho Caio A. S. , Danabasoglu Gokhan , Dirmeyer Paul A. , Doblas-Reyes Francisco J. , Domeisen Daniela I. V. , Ferranti Laura , Ilynia Tatiana , Kumar Arun , Müller Wolfgang A. , Rixen Michel , Robertson Andrew W. , Smith Doug M. , Takaya Yuhei , Tuma Matthias , Vitart Frederic , White Christopher J. , Alvarez Mariano S. , Ardilouze Constantin , Attard Hannah , Baggett Cory , Balmaseda Magdalena A. , Beraki Asmerom F. , Bhattacharjee Partha S. , Bilbao Roberto , de Andrade Felipe M. , DeFlorio Michael J. , Díaz Leandro B. , Ehsan Muhammad Azhar , Fragkoulidis Georgios , Gonzalez Alex O. , Grainger Sam , Green Benjamin W. , Hell Momme C. , Infanti Johnna M. , Isensee Katharina , Kataoka Takahito , Kirtman Ben P. , Klingaman Nicholas P. , Lee June-Yi , Mayer Kirsten , McKay Roseanna , Mecking Jennifer V. , Miller Douglas E. , Neddermann Nele , Justin Ng Ching Ho , Ossó Albert , Pankatz Klaus , Peatman Simon , Pegion Kathy , Perlwitz Judith , Recalde-Coronel G. Cristina , Reintges Annika , Renkl Christoph , Solaraju-Murali Balakrishnan , Spring Aaron , Stan Cristiana , Sun Y. Qiang , Tozer Carly R. , Vigaud Nicolas , Woolnough Steven , Yeager Stephen 
Published: January 2020

Abstract
Weather and climate variations on subseasonal to decadal time scales can have enormous social, economic, and environmental impacts, making skillful predictions on these time scales a valuable tool for decision-makers. As such, there is a growing interest in the scientific, operational, and applications communities in developing forecasts to improve our foreknowledge of extreme events. On subseasonal to seasonal (S2S) time scales, these include high-impact meteorological events such as tropical cyclones, extratropical storms, floods, droughts, and heat and cold waves. On seasonal to decadal (S2D) time scales, while the focus broadly remains similar (e.g., on precipitation, surface and upper-ocean temperatures, and their effects on the probabilities of high-impact meteorological events), understanding the roles of internal variability and externally forced variability such as anthropogenic warming in forecasts also becomes important. The S2S and S2D communities share common scientific and technical challenges. These include forecast initialization and ensemble generation; initialization shock and drift; understanding the onset of model systematic errors; bias correction, calibration, and forecast quality assessment; model resolution; atmosphere–ocean coupling; sources and expectations for predictability; and linking research, operational forecasting, and end-user needs. In September 2018 a coordinated pair of international conferences, framed by the above challenges, was organized jointly by the World Climate Research Programme (WCRP) and the World Weather Research Programme (WWRP). These conferences surveyed the state of S2S and S2D prediction, ongoing research, and future needs, providing an ideal basis for synthesizing current and emerging developments in these areas that promise to enhance future operational services. This article provides such a synthesis.