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.

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Southern Australia's rainfall is highly variable and influenced by factors across scales from synoptic weather to large-scale circulation and remote climate modes of variability. Anthropogenic climate change and natural variability modulate these factors and their interactions. However, studies often focus on changes in selected parts of the climate system with less emphasis on the system as a whole. As such, it is difficult to gain a complete understanding of how southern Australia's rainfall responds to broad-scale changes in the climate system. We step through the existing literature on long-term changes in synoptic-to-large-scale atmospheric circulation and drivers of climate variability to form a more complete story of rainfall changes across southern Australia. This process reveals that the most robust change is the observed winter decline in rainfall as it is consistent with several changing climatic factors: decreasing rainfall from weather systems, strengthening subtropical ridge, poleward shifts in the Hadley Cell and the Southern Annular Mode, and increasing frequency of positive Indian Ocean Dipole events. In other seasons, particularly summer, changes in atmospheric circulation and drivers may not agree with observed rainfall changes, highlighting gaps in our knowledge of atmospheric dynamics and climate change processes. Future work should focus on research across temporal-and spatial-scales, better understanding of jet interactions, the influence of stratospheric processes on the troposphere, and instances of contrasting trends in drivers and southern Australian rainfall changes.