Circulation Conditions’ Effect on the Occurrence of Heat Waves in Western and Southwestern Europe

This article aims to describe the occurrence of heat waves in Western and Southwestern Europe in the period 1976–2015 and determining pressure patterns that cause a persistence of hot days. A hot day was defined as a day on which the daily maximum air temperature was higher than the 95th annual percentile; and a heat wave was recognised as a sequence of at least five days of the abovementioned category. In the discussed multiannual period, this threshold ranged from 23.5 ◦C in Brest to 38.9 ◦C in Seville. Within the analysed area, there were from 14 (Bilbao) to 54 (Montélimar) heat waves observed. The longest heat wave took place in 2003 in Nice and lasted 49 days (14 July–31 August). The occurrence of heat waves within the analysed area was related to the ridge of high pressure located over the area of the study, providing strong solar radiation flux due to cloudlessness or a small cloud cover. Positive SLP, z500 hPa and T850 anomalies occurred over the majority of the research area.