The 2003 summer heat wave and its seasonal forecasting.

The 2003 summer heat wave and its seasonal forecasting. The main features of the heat wave that has affected western Europe during the summer 2003 are first recalled, with particular concern to analogies and differences with previous warm-summer episodes. The skills of the various operational and pre-operational seasonal forecasting models in use at that time are evaluated. None of them has been able to consistently forecast the heat wave three month in advance. The meteorological and climatic situation prevailing during spring 2003 is then analysed. A strong sea-surface-temperature (SST) anomaly is found to have developed over North Atlantic a few months before the heat wave. The particular mechanism at work to explain the occurrence of the heat wave is not a 'simple downwind influence' of the SST anomaly. It very likely involves complex ocean-atmosphere interaction phenomena of a kind that is not properly taken into account in today's seasonal forecasting models. (C) 2004 Academie des sciences. Publie par Elsevier SAS. Tons droits reserves.