An Assessment of Subseasonal Forecast Capability through Global Ensemble

In recent years, requirements for forecast information beyond week-2 has increased significantly for users that provide valuable guidance for public safety, quality of life, and business decisions that drive economic growth. Better understanding of predictability and numerical model capabilities are greatly enhancing our capabilities for prediction beyond week-2, which is known as sub-seasonal to seasonal (S2S) prediction.

The NCEP Global Ensemble Forecast (GEFS) system has been very successful, providing reliable weather and week-2 probabilistic forecast guidance that has translated into valuable information for the general public. But the S2S prediction capabilities of the GEFS have only recently been evaluated. Specifically, these capabilities were evaluated as part of the NOAA SubX (Subseasonal multi-model Experiments) with a 18-year reforecast is used as a reference system. The study proposed here involves a comparison of SubX results with those from the newly developed FV3-based GEFS, which includes a different dynamical core, different horizontal resolution, different micro physics, etc. The upper limits of prediction skill will be investigated through these experiments.

Various metrics will be used to assess the predictability of the system, with dependencies on forecast elements, different spatial/temporal scales, and different forecast regions. The investigation will mainly focus on prediction of the MJO event, associated extratropical circulations, blocking patterns, and other phenomena and processes. Forecast skill will be assessed for both deterministic and probabilistic forecasts in the sub-seasonal time-range.