Comparison of Two Subseasonal Ensemble Forecasting Systems Based on the SLAV Model

The article compares two ensemble forecasting systems, S1 and S2, using the SLAV072L96 model, in terms of forecasts with a lead time of up to 6 weeks. The first system, S1, uses an ensemble of 61 members, and the ensemble of initial states is generated with the help of the breeding method. The newer system, S2, has 41 members, and the ensemble of initial states is prepared using the data assimilation technique based on the local ensemble Kalman filter. It is shown that despite a smaller number of ensemble members, S2 is not inferior to S1; instead, it has some advantages, which are especially remarkable over long integration intervals (up to 46 days). At the same time, both systems are characterized by inadequate spread of the ensemble and asymmetric distribution of forecasted values and hence require additional adjustment and improvement. It is concluded that the use and further development of the S2 system is preferable, since the same or slightly higher quality of ensemble forecasts is achieved with lower computational costs.