SCL Demand Forecast Accuracy: Error, Bias and Worst Miss, 21 August to 20 September 2026
The day-ahead demand forecast for SCL was off by 2.7% on average (mean absolute percentage error) over 695 hours from 21 August to 20 September 2026, and 92% of hours landed within 5% of the reading. Its bias was -1.0%: it ran low on average, an under forecast. The largest miss was 89 MW (9.6%) too high at 22 Aug 2026, 12:00 PDT (UTC-07:00). Dates and times are local (America/Los_Angeles).
Key Facts
- The day-ahead demand forecast for SCL was off by 2.7% on average (mean absolute percentage error) over 695 hours from 21 August to 20 September 2026, and 92% of hours landed within 5% of the reading. Its bias was -1.0%: it ran low on average, an under forecast. The largest miss was 89 MW (9.6%) too high at 22 Aug 2026, 12:00 PDT (UTC-07:00).
- Across 53 US grids ranked by average error over their own latest 30 day windows, SCL came 14 (1 is the smallest error).
- On average the forecast differed from reported demand by 25 MW, against average demand of 938 MW.
- The forecast was above reported demand in 43% of compared hours.
Forecast Error at a Glance
695 hours from 21 August to 20 September 2026Average error2.7%
Bias-1.0%
Hours within 5%92%
Worst miss89 MW
Average error is the mean absolute percentage gap between the forecast and reported demand. Bias is the signed mean (-9 MW per hour on average): the forecast ran low on average, an under forecast. The worst miss was 89 MW (9.6%) too high at 22 Aug 2026, 12:00 PDT (UTC-07:00): forecast 1,012 MW, reported 923 MW.
Source: U.S. Energy Information Administration (EIA). (US Government work, public domain) Data as of 2026-09-20. Accuracy is computed by World Power Monitor from the operator's hourly forecast and reported demand.
Forecast and Reported Demand, Last 7 Days
Local time, to 20 Sept 2026, 18:00 PDT (UTC-07:00)Data to 2026-09-20
| Local hour | Reported demand | Day-ahead forecast |
|---|---|---|
| 13 Sept, 19:00 | 1,056 MW | 1,001 MW |
| 13 Sept, 20:00 | 1,042 MW | 999 MW |
| 13 Sept, 21:00 | 988 MW | 960 MW |
| 13 Sept, 22:00 | 932 MW | 897 MW |
| 13 Sept, 23:00 | 864 MW | 829 MW |
| 14 Sept, 00:00 | 818 MW | 779 MW |
| 14 Sept, 01:00 | 783 MW | 747 MW |
| 14 Sept, 02:00 | 764 MW | 729 MW |
| 14 Sept, 03:00 | 751 MW | 724 MW |
| 14 Sept, 04:00 | 773 MW | 740 MW |
| 14 Sept, 05:00 | 831 MW | 795 MW |
| 14 Sept, 06:00 | 885 MW | 885 MW |
| 14 Sept, 07:00 | 960 MW | 957 MW |
| 14 Sept, 08:00 | 981 MW | 989 MW |
| 14 Sept, 09:00 | 987 MW | 1,006 MW |
| 14 Sept, 10:00 | 989 MW | 1,015 MW |
| 14 Sept, 11:00 | 994 MW | 1,023 MW |
| 14 Sept, 12:00 | 994 MW | 1,026 MW |
| 14 Sept, 13:00 | 1,013 MW | 1,027 MW |
| 14 Sept, 14:00 | 990 MW | 1,025 MW |
| 14 Sept, 15:00 | 997 MW | 1,030 MW |
| 14 Sept, 16:00 | 1,012 MW | 1,048 MW |
| 14 Sept, 17:00 | 1,036 MW | 1,059 MW |
| 14 Sept, 18:00 | 1,032 MW | 1,047 MW |
| 14 Sept, 19:00 | 1,035 MW | 1,042 MW |
| 14 Sept, 20:00 | 1,013 MW | 1,025 MW |
| 14 Sept, 21:00 | 969 MW | 975 MW |
| 14 Sept, 22:00 | 895 MW | 903 MW |
| 14 Sept, 23:00 | 821 MW | 832 MW |
| 15 Sept, 00:00 | 773 MW | 782 MW |
| 15 Sept, 01:00 | 738 MW | 747 MW |
| 15 Sept, 02:00 | 708 MW | 725 MW |
| 15 Sept, 03:00 | 707 MW | 719 MW |
| 15 Sept, 04:00 | 725 MW | 735 MW |
| 15 Sept, 05:00 | 782 MW | 791 MW |
| 15 Sept, 06:00 | 888 MW | 889 MW |
| 15 Sept, 07:00 | 963 MW | 969 MW |
| 15 Sept, 08:00 | 995 MW | 991 MW |
| 15 Sept, 09:00 | 1,004 MW | 1,006 MW |
| 15 Sept, 10:00 | 1,004 MW | 1,014 MW |
| 15 Sept, 11:00 | 1,002 MW | 1,020 MW |
| 15 Sept, 12:00 | 993 MW | 1,027 MW |
| 15 Sept, 13:00 | 984 MW | 1,031 MW |
| 15 Sept, 14:00 | 991 MW | 1,026 MW |
| 15 Sept, 15:00 | 995 MW | 1,030 MW |
| 15 Sept, 16:00 | 1,011 MW | 1,051 MW |
| 15 Sept, 17:00 | 1,023 MW | 1,058 MW |
| 15 Sept, 18:00 | 1,013 MW | 1,044 MW |
| 15 Sept, 19:00 | 1,014 MW | 1,041 MW |
| 15 Sept, 20:00 | 1,008 MW | 1,029 MW |
| 15 Sept, 21:00 | 964 MW | 981 MW |
| 15 Sept, 22:00 | 887 MW | 912 MW |
| 15 Sept, 23:00 | 821 MW | 842 MW |
| 16 Sept, 00:00 | 768 MW | 780 MW |
| 16 Sept, 01:00 | 736 MW | 743 MW |
| 16 Sept, 02:00 | 708 MW | 721 MW |
| 16 Sept, 03:00 | 705 MW | 714 MW |
| 16 Sept, 04:00 | 721 MW | 731 MW |
| 16 Sept, 05:00 | 784 MW | 788 MW |
| 16 Sept, 06:00 | 881 MW | 887 MW |
| 16 Sept, 07:00 | 959 MW | 971 MW |
| 16 Sept, 08:00 | 982 MW | 990 MW |
| 16 Sept, 09:00 | 984 MW | 1,005 MW |
| 16 Sept, 10:00 | 994 MW | 1,015 MW |
| 16 Sept, 11:00 | 994 MW | 1,024 MW |
| 16 Sept, 12:00 | 1,014 MW | 1,032 MW |
| 16 Sept, 13:00 | 1,020 MW | 1,041 MW |
| 16 Sept, 14:00 | 1,026 MW | 1,046 MW |
| 16 Sept, 15:00 | 1,045 MW | 1,055 MW |
| 16 Sept, 16:00 | 1,054 MW | 1,074 MW |
| 16 Sept, 17:00 | 1,075 MW | 1,079 MW |
| 16 Sept, 18:00 | 1,057 MW | 1,058 MW |
| 16 Sept, 19:00 | 1,054 MW | 1,054 MW |
| 16 Sept, 20:00 | 1,044 MW | 1,037 MW |
| 16 Sept, 21:00 | 990 MW | 988 MW |
| 16 Sept, 22:00 | 918 MW | 911 MW |
| 16 Sept, 23:00 | 845 MW | 841 MW |
| 17 Sept, 00:00 | 789 MW | 798 MW |
| 17 Sept, 01:00 | 752 MW | 758 MW |
| 17 Sept, 02:00 | 723 MW | 733 MW |
| 17 Sept, 03:00 | 715 MW | 723 MW |
| 17 Sept, 04:00 | 722 MW | 738 MW |
| 17 Sept, 05:00 | 788 MW | 791 MW |
| 17 Sept, 06:00 | 879 MW | 886 MW |
| 17 Sept, 07:00 | 957 MW | 963 MW |
| 17 Sept, 08:00 | 989 MW | 998 MW |
| 17 Sept, 09:00 | 1,007 MW | 1,018 MW |
| 17 Sept, 10:00 | 1,013 MW | 1,030 MW |
| 17 Sept, 11:00 | 1,033 MW | 1,043 MW |
| 17 Sept, 12:00 | 1,040 MW | 1,053 MW |
| 17 Sept, 13:00 | 1,044 MW | 1,062 MW |
| 17 Sept, 14:00 | 1,050 MW | 1,067 MW |
| 17 Sept, 15:00 | 1,058 MW | 1,080 MW |
| 17 Sept, 16:00 | 1,082 MW | 1,105 MW |
| 17 Sept, 17:00 | 1,098 MW | 1,106 MW |
| 17 Sept, 18:00 | 1,075 MW | 1,079 MW |
| 17 Sept, 19:00 | 1,057 MW | 1,072 MW |
| 17 Sept, 20:00 | 1,040 MW | 1,054 MW |
| 17 Sept, 21:00 | 992 MW | 1,004 MW |
| 17 Sept, 22:00 | 916 MW | 930 MW |
| 17 Sept, 23:00 | 846 MW | 854 MW |
| 18 Sept, 00:00 | 795 MW | 799 MW |
| 18 Sept, 01:00 | 754 MW | 756 MW |
| 18 Sept, 02:00 | 725 MW | 729 MW |
| 18 Sept, 03:00 | 712 MW | 720 MW |
| 18 Sept, 04:00 | 724 MW | 735 MW |
| 18 Sept, 05:00 | 775 MW | 786 MW |
| 18 Sept, 06:00 | 873 MW | 875 MW |
| 18 Sept, 07:00 | 944 MW | 954 MW |
| 18 Sept, 08:00 | 982 MW | 997 MW |
| 18 Sept, 09:00 | 1,004 MW | 1,020 MW |
| 18 Sept, 10:00 | 1,009 MW | 1,031 MW |
| 18 Sept, 11:00 | 1,006 MW | 1,040 MW |
| 18 Sept, 12:00 | 1,002 MW | 1,047 MW |
| 18 Sept, 13:00 | 1,003 MW | 1,055 MW |
| 18 Sept, 14:00 | 1,002 MW | 1,061 MW |
| 18 Sept, 15:00 | 1,020 MW | 1,069 MW |
| 18 Sept, 16:00 | 1,046 MW | 1,088 MW |
| 18 Sept, 17:00 | 1,051 MW | 1,081 MW |
| 18 Sept, 18:00 | 1,017 MW | 1,050 MW |
| 18 Sept, 19:00 | 1,010 MW | 1,037 MW |
| 18 Sept, 20:00 | 986 MW | 1,012 MW |
| 18 Sept, 21:00 | 940 MW | 965 MW |
| 18 Sept, 22:00 | 894 MW | 908 MW |
| 18 Sept, 23:00 | 837 MW | 856 MW |
| 19 Sept, 00:00 | 795 MW | 797 MW |
| 19 Sept, 01:00 | 749 MW | 764 MW |
| 19 Sept, 02:00 | 723 MW | 736 MW |
| 19 Sept, 03:00 | 706 MW | 721 MW |
| 19 Sept, 04:00 | 707 MW | 723 MW |
| 19 Sept, 05:00 | 732 MW | 745 MW |
| 19 Sept, 06:00 | 756 MW | 780 MW |
| 19 Sept, 07:00 | 815 MW | 827 MW |
| 19 Sept, 08:00 | 877 MW | 884 MW |
| 19 Sept, 09:00 | 919 MW | 922 MW |
| 19 Sept, 10:00 | 943 MW | 950 MW |
| 19 Sept, 11:00 | 954 MW | 966 MW |
| 19 Sept, 12:00 | 957 MW | 965 MW |
| 19 Sept, 13:00 | 946 MW | 962 MW |
| 19 Sept, 14:00 | 923 MW | 959 MW |
| 19 Sept, 15:00 | 912 MW | 957 MW |
| 19 Sept, 16:00 | 929 MW | 971 MW |
| 19 Sept, 17:00 | 940 MW | 988 MW |
| 19 Sept, 18:00 | 949 MW | 986 MW |
| 19 Sept, 19:00 | 959 MW | 996 MW |
| 19 Sept, 20:00 | 951 MW | 979 MW |
| 19 Sept, 21:00 | 922 MW | 943 MW |
| 19 Sept, 22:00 | 875 MW | 894 MW |
| 19 Sept, 23:00 | 821 MW | 845 MW |
| 20 Sept, 00:00 | 780 MW | 791 MW |
| 20 Sept, 01:00 | 742 MW | 751 MW |
| 20 Sept, 02:00 | 714 MW | 727 MW |
| 20 Sept, 03:00 | 708 MW | 714 MW |
| 20 Sept, 04:00 | 701 MW | 715 MW |
| 20 Sept, 05:00 | 719 MW | 734 MW |
| 20 Sept, 06:00 | 744 MW | 768 MW |
| 20 Sept, 07:00 | 795 MW | 808 MW |
| 20 Sept, 08:00 | 842 MW | 861 MW |
| 20 Sept, 09:00 | 877 MW | 904 MW |
| 20 Sept, 10:00 | 895 MW | 928 MW |
| 20 Sept, 11:00 | 903 MW | 940 MW |
| 20 Sept, 12:00 | 910 MW | 945 MW |
| 20 Sept, 13:00 | 927 MW | 945 MW |
| 20 Sept, 14:00 | 921 MW | 945 MW |
| 20 Sept, 15:00 | 939 MW | 946 MW |
| 20 Sept, 16:00 | 893 MW | 964 MW |
| 20 Sept, 17:00 | 997 MW | 997 MW |
| 20 Sept, 18:00 | 1,014 MW | 1,014 MW |
Assumptions
- Only hours with both a forecast and a positive demand reading count (695 of 720 hours in the window). Missing and zero values, and readings under 30% or over 3 times the grid's own median for the window, are treated as reporting faults and left out.
- Error is (forecast minus reported demand) divided by reported demand; average error uses absolute values so high and low misses do not cancel. Bias keeps the sign and does cancel.
- Reported demand is preliminary and may be revised. A 30 day window is a short sample and one heat wave or holiday can move these figures.
- US figures are for the EIA balancing authority or region named on this page. US and European grids are ranked separately.