Assessment of the Climate Forecast System Version 2 and the Effects of ENSO/NAO on Predictive Skill

Subseasonal to seasonal (S2S) prediction, with forecast lead times from 2 weeks to a season, is of considerable socioeconomic value as the products are utilized across many sectors (e.g. energy, agriculture, public health, etc.). In order to improve our current forecast capabilities, models must be continuously assessed in order to discover where improvements can be made. One particular focus is to identify sources of predictability and evaluate their representations in operational models. Low frequency climate modes are a key source of predictability on the subseasonal to seasonal time scales, and such modes may modulate prediction skill of the mid-latitude atmosphere. The 200-hPa geopotential height from the Climate Forecast System Version 2 (CFSv2) reforecasts are used to assess the effects that low frequency climate modes, specifically the ENSO and the NAO, have on the northern hemisphere winter predictability. In addition, the representation of teleconnections between tropics and extratropics in the CFSv2 are evaluated through the analysis of 200-hPa geopotential height, precipitation rate, and sea surface temperature data, with the objective to identify the windows of high predictability and assist in model improvements.