Record May temperatures swept Europe from 24-28 May. The UK recorded 35.1C at Kew Gardens on Monday 26 May (a May record), Paris sat 14C above seasonal normal, and Ireland logged 28.8C at Clonmel and Killarney (a national May record). The blocking high held for five days, compressing the window for overnight cooling and sustaining daytime electricity demand across the continent.
The energy market consequence is a competition for gas-fired generation between cooling demand and storage injection. Storage injection on 28 May showed only a 0.3 percentage-point daily gain. French nuclear export capacity, which has been suppressing the FR-DE spread all year on EDF's 350-370 TWh full-year guidance, faced a domestic cooling load precisely when German importers needed cross-border flows most. The spread doubled to €46.58 on 21 May, and the heatwave pushed domestic French demand further into nuclear capacity that would otherwise have crossed the interconnector.
The 0.3 pp daily gain did not break the trajectory. The 45 GWh/day margin survived the May event. The forward risk is a June repeat: at higher baseline temperatures, the buffer disappears into cooling demand before the injection season's strongest months arrive.
