Observational needs for advancing subseasonal-to-seasonal forecasting systems: an ECMWF perspective

Monitoring and forecasting weather and climate variations to serve societal needs are major community endeavours, relying on a suitable and sustained observing system and high quality numerical models able to integrate the observational information and propagate it into the future. Here we present lessons learnt from ECMWF the subseasonal-to-seasonal forecasting systems and we identify outstanding gaps in the chain that enables advances in integrated forecasts system: observations - process understanding - model/data assimilation development.