The European heat wave and drought event during the summer of 2003 emerged as the result of a pronounced split flow in the Northern Hemisphere. Upper level features as well as normal seasonal changes, favored the formation and placement of cyclones and anticyclones observed during the summer. There are several atmospheric and oceanic variables that show a strong feedback mechanism. Westerly wind speed variability caused a series of fluctuations in upper level height patterns between June, July, August and September.

Suggested relationships to the anomalous event include teleconnections from the Southern Atlantic, Sahel region of Africa, the Tropical Atlantic, North-Eastern Pacific, Mediterranean, and North-Central Atlantic. The atmospheric variable of greatest interest is precipitable water due to its apparent positive trend with the upper level wind speed fluctuation.

Forecast skill of the EMCWF for European heat waves was relatively low. Investigations into low forecast skill conclude the poorly initialized variable was soil moisture. Lack of adequate measurements and integration of soil moisture values into models has been determined to be the cause of low skill score, thus calling for a revision of model influence from soil moisture.