How far in advance can we predict changes in large-scale flow leading to severe cold conditions over Europe?

The potential of early warning for severe cold conditions is explored using the Subseasonal to Seasonal (S2S) Prediction research project data archive. We explore the use of a two-dimensional phase space based on the leading empirical orthogonal functions (EOFs) of mid-tropospheric flow computed over the Euro-Atlantic region in order to study the time evolution of flow patterns associated with high-impact temperature anomalies. We find that the phase space is an effective tool for monitoring predictions of regime transitions at medium and extended ranges. We show that a number of S2S systems have some skill in the prediction of cold spells over Europe, even beyond the medium range. In particular, the ECMWF (European Centre for Medium-Range Weather Forecasts) model represents well the observed preferential transition paths. We reveal that the impact of the Madden-Julian Oscillation (MJO) on the predictive skill of large-scale flow over Europe is asymmetric. The impact of the MJO on the Brier skill scores and reliability is significantly positive for predictions of the negative phase of the North Atlantic Oscillation (NAO): beyond week one, forecasts with the MJO in their initial state are significantly more reliable than forecasts with no MJO in their initial conditions. In contrast, the predictive skill for positive NAO shows little sensitivity to the MJO.