For this session we are aiming to organise it according to the SPARK concept: https://www.ems2020.eu/programme_and_abstracts/on_the_programme/spark_sessions.html .
The session will focus on the most recent developments in the field of ensemble techniques, ranging from its close connections with data-assimilation and nowcasting at short and medium ranges to their capacity to produce and deliver skillful and reliable forecasts of high-impact extreme events at sub-seasonal to seasonal (S2S) timescales.
As such it may provide a platform for exchanging ideas on how to create and use an ensemble system, techniques varying according to the forecast lead time. In particular, the forecaster perspective and the use of ensembles in predicting hazardous weather will be of interest.

The conveners invite papers on various issues associated with Ensemble Forecasting for weather prediction, such as:
• representation of initial uncertainties in Global and Limited-Area Ensemble Prediction Systems, including interlinks between data-assimilation and probabilistic forecasting;
• representation of model or boundary uncertainties in Global and Limited-Area Ensemble Prediction Systems;
• results from experiments including THORPEX Regional Campaigns, HyMeX, FROST-2014, etc.;
• results from recent studies using TIGGE and TIGGE-LAM databases;
• use, verification and calibration methods of Ensemble Prediction Systems;
• applications of probabilistic forecasts in the sectors of energy, health, transport, agriculture, insurance and finance;
• challenges tackled by the S2S WWRP/THORPEX-WCRP joint project (http://s2sprediction.net), including discussion on S2S sources of predictability, forecasts and socioeconomic applications of high-impact climate services.

Participants are especially encouraged to present contributions and discuss strategies to bridge gaps between stakeholders and actionable S2S tailored products.