Weather Ensemble

What this spread means

Weather forecasts are uncertain, so ECMWF produces many plausible scenarios for how conditions may develop. We use each scenario to estimate how wind, solar, electricity demand, and prices could respond. The inner band contains the central 50% of those results and the outer band the central 80%. Wider bands mean weather uncertainty has a larger effect on the forecast.

These ranges capture weather uncertainty only. Outages, non-weather changes in demand, market behavior, and model errors can still move the actual outcome outside them. The solid line uses ECMWF's separate best-estimate weather forecast, while the dashed line is the average across the ensemble scenarios. They use different weather inputs and therefore do not need to match.