Day-Ahead Load Forecast Accuracy of U.S. Balancing Authorities, 2015–2026: A Scorecard from Public EIA-930 Data (Cardinal Grid Notes, No. 1)

Balancing authorities in the contiguous United States report to the U.S. Energy Information Administration, through Form EIA-930, both the hourly demand that occurred and the day-ahead demand forecast they produced the previous day. This note scores those forecasts for the full public record, from 2015-07-01 to 2026-09-10, with explicit data-quality rules. Of 72 BAs in the files, 58 report both series and 42 are eligible for ranking. The demand-weighted day-ahead MAPE across eligible BAs is 3.56%; at the hour of the daily peak the forecast was below actual demand on 59% of eligible BA-days, a share that has increased since 2019. The highest error values are dominated by reporting problems rather than forecasting problems. Code, results and the event calendar are open. Web version: cardinalgrid.com/notes. Source and reproducible analysis: github.com/cardinalgrid/notes.