Statistics
Page built 2026-09-21
Data as of 2026-09-20
Search
Built 2026-09-21 (21 September 2026)

ISO-NE Demand Forecast Accuracy: Error, Bias and Worst Miss, 21 August to 20 September 2026

The day-ahead demand forecast for ISO-NE was off by 3.0% on average (mean absolute percentage error) over 719 hours from 21 August to 20 September 2026, and 76% of hours landed within 5% of the reading. Its bias was -2.5%: it ran low on average, an under forecast. The largest miss was 1,425 MW (11.2%) too low at 27 Aug 2026, 04:00 EDT (UTC-04:00). Dates and times are local (America/New_York).

Key Facts

  • The day-ahead demand forecast for ISO-NE was off by 3.0% on average (mean absolute percentage error) over 719 hours from 21 August to 20 September 2026, and 76% of hours landed within 5% of the reading. Its bias was -2.5%: it ran low on average, an under forecast. The largest miss was 1,425 MW (11.2%) too low at 27 Aug 2026, 04:00 EDT (UTC-04:00).
  • Across 53 US grids ranked by average error over their own latest 30 day windows, ISO-NE came 18 (1 is the smallest error).
  • On average the forecast differed from reported demand by 362 MW, against average demand of 12,974 MW.
  • The forecast was above reported demand in 22% of compared hours.

Forecast Error at a Glance

719 hours from 21 August to 20 September 2026
Average error3.0%
Bias-2.5%
Hours within 5%76%
Worst miss1,425 MW

Average error is the mean absolute percentage gap between the forecast and reported demand. Bias is the signed mean (-292 MW per hour on average): the forecast ran low on average, an under forecast. The worst miss was 1,425 MW (11.2%) too low at 27 Aug 2026, 04:00 EDT (UTC-04:00): forecast 11,290 MW, reported 12,715 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, 21:00 EDT (UTC-04:00)
ISO-NE day-ahead demand forecast and reported demand by hour Hourly reported demand and the day-ahead forecast for ISO-NE over the last 7 days of the window, to 20 Sept 2026, 21:00 EDT (UTC-04:00). Gaps are hours with a missing, zero or implausible report. 0 5,000 10,000 15,000 20,000 13 Sept, 22:0014 Sept, 22:0015 Sept, 22:0016 Sept, 22:0017 Sept, 22:0018 Sept, 22:0019 Sept, 22:00
Hourly reported demand and the day-ahead forecast for ISO-NE over the last 7 days of the window, to 20 Sept 2026, 21:00 EDT (UTC-04:00). Gaps are hours with a missing, zero or implausible report.
Data to 2026-09-20
ISO-NE day-ahead demand forecast and reported demand by hour
Local hourReported demandDay-ahead forecast
13 Sept, 22:0013,140 MW13,030 MW
13 Sept, 23:0012,186 MW12,160 MW
14 Sept, 00:0011,505 MW11,960 MW
14 Sept, 01:0011,325 MW11,390 MW
14 Sept, 02:0011,064 MW11,010 MW
14 Sept, 03:0010,993 MW10,930 MW
14 Sept, 04:0011,225 MW10,970 MW
14 Sept, 05:0011,971 MW11,660 MW
14 Sept, 06:0012,877 MW12,820 MW
14 Sept, 07:0013,352 MW13,260 MW
14 Sept, 08:0012,624 MW12,530 MW
14 Sept, 09:0011,430 MW11,360 MW
14 Sept, 10:0010,552 MW10,240 MW
14 Sept, 11:0010,325 MW9,630 MW
14 Sept, 12:0010,515 MW9,560 MW
14 Sept, 13:0010,659 MW9,810 MW
14 Sept, 14:0010,597 MW10,150 MW
14 Sept, 15:0011,252 MW10,840 MW
14 Sept, 16:0012,425 MW12,540 MW
14 Sept, 17:0014,088 MW14,400 MW
14 Sept, 18:0014,870 MW15,160 MW
14 Sept, 19:0014,866 MW15,090 MW
14 Sept, 20:0014,253 MW14,560 MW
14 Sept, 21:0013,322 MW13,450 MW
14 Sept, 22:0012,165 MW12,270 MW
14 Sept, 23:0011,101 MW11,220 MW
15 Sept, 00:0010,661 MW10,580 MW
15 Sept, 01:0010,745 MW10,120 MW
15 Sept, 02:0010,552 MW9,820 MW
15 Sept, 03:0010,430 MW9,700 MW
15 Sept, 04:0010,293 MW9,940 MW
15 Sept, 05:0010,487 MW10,670 MW
15 Sept, 06:0011,529 MW11,810 MW
15 Sept, 07:0011,692 MW12,020 MW
15 Sept, 08:0010,581 MW10,540 MW
15 Sept, 09:009,870 MW9,280 MW
15 Sept, 10:009,385 MW8,510 MW
15 Sept, 11:009,026 MW8,240 MW
15 Sept, 12:009,004 MW8,210 MW
15 Sept, 13:009,266 MW8,650 MW
15 Sept, 14:009,449 MW9,300 MW
15 Sept, 15:0010,189 MW9,940 MW
15 Sept, 16:0011,630 MW11,620 MW
15 Sept, 17:0013,450 MW13,190 MW
15 Sept, 18:0014,337 MW14,200 MW
15 Sept, 19:0014,498 MW14,500 MW
15 Sept, 20:0013,962 MW14,080 MW
15 Sept, 21:0013,116 MW13,160 MW
15 Sept, 22:0012,083 MW12,130 MW
15 Sept, 23:0011,271 MW11,150 MW
16 Sept, 00:0011,139 MW10,350 MW
16 Sept, 01:0010,886 MW9,940 MW
16 Sept, 02:0010,611 MW9,670 MW
16 Sept, 03:0010,542 MW9,600 MW
16 Sept, 04:0010,759 MW9,840 MW
16 Sept, 05:0010,876 MW10,610 MW
16 Sept, 06:0011,770 MW11,850 MW
16 Sept, 07:0012,303 MW12,200 MW
16 Sept, 08:0011,980 MW11,940 MW
16 Sept, 09:0010,923 MW10,990 MW
16 Sept, 10:0010,300 MW10,020 MW
16 Sept, 11:0010,451 MW9,820 MW
16 Sept, 12:0010,495 MW9,950 MW
16 Sept, 13:0011,106 MW10,450 MW
16 Sept, 14:0011,570 MW11,190 MW
16 Sept, 15:0012,293 MW12,190 MW
16 Sept, 16:0013,644 MW13,500 MW
16 Sept, 17:0014,978 MW14,690 MW
16 Sept, 18:0015,643 MW15,370 MW
16 Sept, 19:0015,854 MW15,550 MW
16 Sept, 20:0015,389 MW15,040 MW
16 Sept, 21:0014,554 MW14,120 MW
16 Sept, 22:0013,494 MW13,040 MW
16 Sept, 23:0012,442 MW12,010 MW
17 Sept, 00:0012,045 MW11,660 MW
17 Sept, 01:0011,580 MW11,180 MW
17 Sept, 02:0011,366 MW10,830 MW
17 Sept, 03:0011,405 MW10,750 MW
17 Sept, 04:0011,579 MW10,870 MW
17 Sept, 05:0012,110 MW11,550 MW
17 Sept, 06:0013,096 MW12,790 MW
17 Sept, 07:0013,575 MW13,320 MW
17 Sept, 08:0013,288 MW13,010 MW
17 Sept, 09:0012,921 MW12,710 MW
17 Sept, 10:0012,786 MW12,700 MW
17 Sept, 11:0013,213 MW13,180 MW
17 Sept, 12:0014,009 MW13,760 MW
17 Sept, 13:0014,642 MW14,340 MW
17 Sept, 14:0015,266 MW14,910 MW
17 Sept, 15:0015,986 MW15,470 MW
17 Sept, 16:0016,606 MW16,820 MW
17 Sept, 17:0016,952 MW16,900 MW
17 Sept, 18:0017,055 MW16,980 MW
17 Sept, 19:0017,038 MW17,000 MW
17 Sept, 20:0016,524 MW16,370 MW
17 Sept, 21:0015,677 MW15,400 MW
17 Sept, 22:0014,593 MW14,240 MW
17 Sept, 23:0013,586 MW13,200 MW
18 Sept, 00:0013,075 MW12,440 MW
18 Sept, 01:0012,919 MW11,770 MW
18 Sept, 02:0012,329 MW11,550 MW
18 Sept, 03:0012,301 MW11,220 MW
18 Sept, 04:0012,146 MW11,370 MW
18 Sept, 05:0012,970 MW11,980 MW
18 Sept, 06:0013,400 MW13,180 MW
18 Sept, 07:0013,739 MW13,610 MW
18 Sept, 08:0013,183 MW13,360 MW
18 Sept, 09:0012,675 MW12,620 MW
18 Sept, 10:0012,227 MW12,320 MW
18 Sept, 11:0012,027 MW12,030 MW
18 Sept, 12:0012,032 MW12,250 MW
18 Sept, 13:0012,494 MW12,310 MW
18 Sept, 14:0012,996 MW12,910 MW
18 Sept, 15:0013,674 MW13,840 MW
18 Sept, 16:0014,564 MW14,690 MW
18 Sept, 17:0015,659 MW15,690 MW
18 Sept, 18:0015,971 MW15,850 MW
18 Sept, 19:0015,705 MW15,800 MW
18 Sept, 20:0015,007 MW15,110 MW
18 Sept, 21:0014,148 MW14,110 MW
18 Sept, 22:0013,129 MW12,970 MW
18 Sept, 23:0012,248 MW11,980 MW
19 Sept, 00:0011,453 MW10,870 MW
19 Sept, 01:0010,855 MW10,210 MW
19 Sept, 02:0010,487 MW9,880 MW
19 Sept, 03:0010,239 MW9,630 MW
19 Sept, 04:0010,377 MW9,570 MW
19 Sept, 05:0010,482 MW9,790 MW
19 Sept, 06:0010,479 MW10,230 MW
19 Sept, 07:0010,256 MW10,190 MW
19 Sept, 08:009,344 MW9,330 MW
19 Sept, 09:008,599 MW8,330 MW
19 Sept, 10:008,509 MW7,620 MW
19 Sept, 11:008,428 MW7,330 MW
19 Sept, 12:008,274 MW7,330 MW
19 Sept, 13:008,520 MW7,570 MW
19 Sept, 14:008,909 MW7,940 MW
19 Sept, 15:009,676 MW9,020 MW
19 Sept, 16:0010,773 MW10,930 MW
19 Sept, 17:0012,077 MW12,510 MW
19 Sept, 18:0012,818 MW13,360 MW
19 Sept, 19:0012,979 MW13,800 MW
19 Sept, 20:0012,566 MW13,020 MW
19 Sept, 21:0011,977 MW12,210 MW
19 Sept, 22:0011,267 MW11,360 MW
19 Sept, 23:0010,543 MW10,550 MW
20 Sept, 00:0010,341 MW10,020 MW
20 Sept, 01:0010,250 MW9,570 MW
20 Sept, 02:0010,028 MW9,300 MW
20 Sept, 03:009,883 MW9,140 MW
20 Sept, 04:009,887 MW9,120 MW
20 Sept, 05:0010,023 MW9,280 MW
20 Sept, 06:0010,378 MW9,610 MW
20 Sept, 07:0010,783 MW9,920 MW
20 Sept, 08:0011,088 MW10,340 MW
20 Sept, 09:0011,545 MW10,690 MW
20 Sept, 10:0011,433 MW11,020 MW
20 Sept, 11:0011,732 MW11,750 MW
20 Sept, 12:0012,122 MW12,070 MW
20 Sept, 13:0012,443 MW12,520 MW
20 Sept, 14:0012,517 MW12,470 MW
20 Sept, 15:0012,606 MW12,560 MW
20 Sept, 16:0013,022 MW13,010 MW
20 Sept, 17:0013,490 MW13,460 MW
20 Sept, 18:0013,739 MW13,690 MW
20 Sept, 19:0013,648 MW13,800 MW
20 Sept, 20:0013,120 MW13,010 MW
20 Sept, 21:0012,361 MW12,210 MW

Assumptions

  • Only hours with both a forecast and a positive demand reading count (719 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.