Current and Emerging Developments in Subseasonal to Decadal Prediction

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.

The physics of climate variability and climate change

“…Still, there are increasing efforts for achieving "seemless prediction" across time and space scales (e.g., Palmer et al, 2008;Robertson and Vitart, 2018). Merryfield et al (2020) provide a comprehensive review of the most recent efforts for bridging the gap between S2S and seasonal-to-decadal prediction.…”

Stratospheric drivers of extreme events at the Earth’s surface

“…here is increasing demand for skillful prediction of weather impacts, especially for lead times beyond regular weather forecasts of 7-10 days 1 . Although a range of surface components of the coupled ocean-atmosphere system have been identified as sources of predictability on sub-seasonal to decadal timescales, i.e., for weeks to decades 2 , another potential source of predictability arises from the stratosphere 3 at 10-50 km above the Earth's surface. The stratosphere exhibits an overall slower evolution and longer predictability as compared to the troposphere 4 , and a downward influence from the stratosphere can thus contribute to persistent and predictable changes at the surface on timescales of weeks to years.…”

Subseasonal to Seasonal Prediction of Weather to Climate with Application to Tropical Cyclones

“…Besides improving the forecast products based on better hindcasting sets, many ideas have been put forward toward improving the model forecasts themselves, through model improvements and better initialization, many of which were discussed at the International Conferences on Subseasonal to Decadal Prediction, held in Boulder, CO, in September 2018 (Merryfield et al, ). Most current operational systems are initializing each model component separately.…”