A sharp contrast between persistent heat and a mid-month cold outbreak defined European weather in May and shaped solar conditions across the continent, said
analysis using the Solcast API. A blocking high over central and western Europe brought clear skies, increased insolation and unusually high temperatures to much of the country.
continent later in the month. In contrast, Arctic air moved south in mid-month, bringing clouds and thunderstorms that heralded what would otherwise be a strong month for solar. While much of Europe ended up sunnier than normal, areas beyond the blocking height experienced below-average insolation.
The dominant feature during the latter part of the month was a blocking high that trapped warm air from Africa over much of Europe. This limited cloud development created sunnier than usual conditions from Spain to Ukraine. The clear skies coincided with record temperatures, with several countries reporting records broken by several degrees and daily temperatures up to 10 C above average. In terms of solar conditions, the strongest irradiance anomalies were concentrated around Austria, where levels were as much as 25% above normal.
This pattern differed from the middle of the month, when a cold upper-level system moved Arctic air south into the Mediterranean and Africa. That colder air disrupted the warm conditions that had developed earlier this month, bringing more clouds and heavy thunderstorms. This reduced insolation in the affected areas and interrupted what had been a sunny start to May. As a result, despite the later heat wave, 2026 became only the seventh warmest month on record.
The benefits of the blocking high were not evenly distributed. In areas further from the center of the heat dome, irradiation results were weaker and conditions were more uncertain. Scotland and Ireland finished around 5% below average, while parts of Norway recorded the largest deficits, around 15% below normal. These regions were closer to the edge of the blocking pattern, where cloud and storm activity were more likely to develop, even though central Europe remained relatively clear.
Solcast produces these figures by tracking clouds and aerosols worldwide at a resolution of 1-2 km, using proprietary satellite data AI/ML algorithms. This data is used to drive irradiance models, allowing Solcast to calculate high-resolution irradiance, with a typical deviation of less than 2%, as well as cloud tracking predictions. This data is used by more than 350 companies that manage more than 300 GW of solar energy worldwide.
