Evaluating NOAA Climate Forecast System Global Subseasonal Forecasts with an Emphasis on Tropical Convection

This presentation describes the subseasonal predictive skill of the NOAA Climate Forecast System version 2 (CFSv2), focusing on the spatial and temporal distributions of error for large-scale atmospheric variables and the realism of simulated tropical convection. Forecasts are evaluated at a range of temporal scales and lead times. Errors for geopotential height and velocity potential forecasts saturate at leads of 3-5 weeks, with little/no skill over climatology after week-2. Sea surface temperatures retain predictability longer than atmospheric variables. Significant forecast biases, particularly in tropical convection and moisture, are found within CFSv2 and their connection to the overall prediction of convection is discussed. The realism of simulated tropical convection and associated teleconnections degrades with forecast lead time. Large-scale tropical convection in CFSv2 is more stationary than observed. Forecast MJOs propagate eastward too slowly and those initiated over the Indian Ocean have trouble traversing beyond the Maritime Continent. These flaws in simulated tropical convection, which could be tied to problems with convective parameterization and associated mean state biases, affect atmospheric teleconnections and may thus degrade extended global forecast skill.