Subseasonal Predictions of the Ethiopian Belg Rains

This study builds from knowledge of the role of tropical-extratropical interactions in modulating February to May (Belg) seasonal rainfall to study predictability on the sub-seasonal time scale. Earlier study has identified two modes of regional circulation patterns that modulate Belg rainfall variability. A ridge/trough pattern, featuring two anomalous mid-upper level warm anticyclones and one cold cyclonic trough in the region between the Northeast Atlantic and the Arabian Peninsula, tends to suppress the Belg rainfall by way of weakening tropical-extratropical interactions. In contrast, a tripole structure with two anomalous mid-upper level cold cyclonic troughs and one warm anticyclone tends to enhance rainfall during the Belg season of Ethiopia. Based on these findings, we construct atmospheric indices that reflect this teleconnection pattern to the Belg subseasonal variability. The predictability of these indices in the NCEP/GEFS and CFSv2 is also discussed. These indices are combined with other teleconnection patterns including the NAO, and the MJO to improve the Belg sub-seasonal rainfall forecasts at week-2 time scale. Standard verification methods including Heidke and Brier skill scores are used to verify the forecasts.