This study investigated the drivers and extended-range prediction of the mid-July to early August 2018 heatwaves over northwestern Europe, focusing on regional heatwave events over Scandinavia (SC) and Western Europe (WE). The persistent blocking regime (BL) was the most influential contributor for the 2018 heatwave over SC, with the Atlantic Low regime (AL) and North Atlantic Oscillation (NAO) as secondary contributors. The major contributor to the WE heatwave was AL. A multi-model ensemble of real-time forecasts captured the evolution of warm spells up to 3 weeks in advance, but heatwave occurrence and significance predictions were unsatisfactory. BL and AL could be predicted 2 weeks in advance, leading to successful warm spell predictions.

Mien-Tze Kueh, Chuan-Yao Lin