The prediction, one season ahead, of summer heat waves in Europe remains a challenge. A new study shows that summer heat in Europe rarely develops after rainy winter and spring seasons over Southern Europe. Conversely dry seasons are either followed by hot or cold summers. The predictability of summer heat is therefore asymmetric. Climate projections indicate a drying of Southern Europe. The study suggests that this asymmetry should create a favorable situation for the development of more summer heat waves with however a modified seasonal predictability from winter and spring rainfall.