Higher Subseasonal Predictability of Extreme Hot European Summer Temperatures as Compared to Average Summers

Summer temperatures in the last decades were increasingly characterized by persistent extremes, and there is evidence that this trend will continue in a warming climate. The exact timing of these extremes is less well known, and it is therefore crucial to consider their subseasonal predictability. We compare the prediction of summer 2m-temperature extremes in Europe with the prediction of average events for four subseasonal forecasting systems. We find higher prediction skill for warm extremes as compared to average events, with some regional dependence. The same is not true for cold extremes, indicating an asymmetry in the processes causing opposite summer temperature extremes. The forecast skill is strongly increased by the most severe and persistent events in the analyzed period. We hypothesize that the enhanced warm extreme skill is related to persistent flow patterns and land-atmosphere interaction. This could have implications for potentially enhanced predictability in a warming climate.