Convective-Permitting Modeling for Retrospective Subseasonal-to-Seasonal (S2S) Forecasting Using the Framework of the Coordinated Regional Ensemble Downscaling Experiment (CORDEX)

Convective-permitting modeling (CPM) yields step improvements in the representation of precipitation, as has been demonstrated in applications of numerical weather prediction and climate modeling. While CPM has been used in the context of historical climate simulations and climate change projections, its application to the sub-seasonal to seasonal (S2S) forecast timescale (weeks to months) is comparatively underexplored. New, long-term S2S reforecast products have recently been generated from operational global forecast models, for example as part of the S2S Project and North American Multimodel Ensemble (NMME). These are analogous to CMIP models used for climate change projection. It is now technically possible to dynamically downscale these reforecast data to CPM scale, to asess potential improvement in S2S forecast skill and create new S2S forecast metrics for extreme events. The Coordinated Regional Ensemble Downscaling Experiment (CORDEX) provides an existing robust community framework that can be leveraged to dynamically downscale S2S reforecast data, in a globally unified way. This overview presentation will highlight outcomes from a community discussion on this topic that took place at the 2019 Latsis Symposium "High-Resolution Climate Modeling: Perspectives and Challenges" at ETH Zurich, including a summary of the current state of the science, collective identification of research priorities, and proposed action items proceeding forward.