A simplified seasonal forecasting strategy, applied to wind and solar power in Europe

•The skill in seasonal forecasts of wind and irradiance in Europe is patchy.•A linear regression method can produce calibrated probabilistic seasonal forecasts.•Seasonal + regional average wind/solar power is highly-correlated with wind/irradiance.•So, detailed transformations (power curves etc.) are not necessary at these scales.•Together these results simplify the production of seasonal climate services.