As Randall [1] explains, in recent years atmospheric science has been “struggling to understand a very large and powerful tropical weather system called the Madden-Julian oscillation, or MJO. The MJO occurs mainly over the remote tropical oceans and was not discovered until the early 1970s. It strongly influences precipitation over southern Asia and northern Australia, affecting the lives of literally billions of people. It is also believed to influence the timing and intensity of El Niños. Despite its im-portance, the MJO is perhaps the last type of weather system for which the basic physi-cal mechanisms are not well understood.” Following Hottovy [2], 10 years after Ran-dall, one can state that nowadays “there is a lot of hypotheses about basic physical mechanisms of the MJO but not a consensus on them.”

Sub-seasonal (also referred to as extended-range) prediction, looking about two weeks to one month ahead, can provide vital early warning of weather extremes and is a key area of research and operational interest. Improving forecasts of extreme events is also a key goal within ECMWF’s Strategy. We are ECMWF scientists working on sub-seasonal prediction of extreme weather events in Europe leveraging pattern-based forecasting, as part of the EU-funded Climate Advanced Forecasting of sub-seasonal Extremes (CAFE) project. The four-year CAFE project is now drawing to a close and we share the main findings from our projects here.