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Data as of 2026-09-20
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Built 2026-09-21 (21 September 2026)

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

The day-ahead demand forecast for NYISO was off by 2.6% on average (mean absolute percentage error) over 695 hours from 21 August to 20 September 2026, and 89% of hours landed within 5% of the reading. Its bias was -2.0%: it ran low on average, an under forecast. The largest miss was 1,698 MW (7.6%) too low at 17 Sept 2026, 16:00 EDT (UTC-04:00). Dates and times are local (America/New_York).

Key Facts

  • The day-ahead demand forecast for NYISO was off by 2.6% on average (mean absolute percentage error) over 695 hours from 21 August to 20 September 2026, and 89% of hours landed within 5% of the reading. Its bias was -2.0%: it ran low on average, an under forecast. The largest miss was 1,698 MW (7.6%) too low at 17 Sept 2026, 16:00 EDT (UTC-04:00).
  • Across 53 US grids ranked by average error over their own latest 30 day windows, NYISO came 11 (1 is the smallest error).
  • On average the forecast differed from reported demand by 460 MW, against average demand of 17,652 MW.
  • The forecast was above reported demand in 21% of compared hours.

Forecast Error at a Glance

695 hours from 21 August to 20 September 2026
Average error2.6%
Bias-2.0%
Hours within 5%89%
Worst miss1,698 MW

Average error is the mean absolute percentage gap between the forecast and reported demand. Bias is the signed mean (-339 MW per hour on average): the forecast ran low on average, an under forecast. The worst miss was 1,698 MW (7.6%) too low at 17 Sept 2026, 16:00 EDT (UTC-04:00): forecast 20,779 MW, reported 22,477 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)
NYISO day-ahead demand forecast and reported demand by hour Hourly reported demand and the day-ahead forecast for NYISO 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 6,250 12,500 18,750 25,000 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 NYISO 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
NYISO day-ahead demand forecast and reported demand by hour
Local hourReported demandDay-ahead forecast
13 Sept, 22:0019,213 MW18,713 MW
13 Sept, 23:0018,081 MW17,612 MW
14 Sept, 00:0017,148 MW16,959 MW
14 Sept, 01:0016,419 MW16,193 MW
14 Sept, 02:0015,900 MW15,618 MW
14 Sept, 03:0015,563 MW15,264 MW
14 Sept, 04:0015,535 MW15,226 MW
14 Sept, 05:0016,087 MW15,751 MW
14 Sept, 06:0017,225 MW16,783 MW
14 Sept, 07:0017,590 MW17,114 MW
14 Sept, 08:0016,976 MW16,725 MW
14 Sept, 09:0016,161 MW16,012 MW
14 Sept, 10:0015,815 MW15,508 MW
14 Sept, 11:0015,758 MW15,350 MW
14 Sept, 12:0015,966 MW15,349 MW
14 Sept, 13:0016,276 MW15,518 MW
14 Sept, 14:0016,469 MW15,716 MW
14 Sept, 15:0016,913 MW16,210 MW
14 Sept, 16:0017,644 MW16,949 MW
14 Sept, 17:0018,616 MW17,781 MW
14 Sept, 18:0019,270 MW18,338 MW
14 Sept, 19:0019,266 MW18,723 MW
14 Sept, 20:0018,694 MW18,346 MW
14 Sept, 21:0017,717 MW17,440 MW
14 Sept, 22:0016,559 MW16,394 MW
14 Sept, 23:0015,478 MW15,349 MW
15 Sept, 00:0014,632 MW14,614 MW
15 Sept, 01:0014,011 MW13,992 MW
15 Sept, 02:0013,603 MW13,598 MW
15 Sept, 03:0013,390 MW13,404 MW
15 Sept, 04:0013,465 MW13,475 MW
15 Sept, 05:0014,056 MW14,077 MW
15 Sept, 06:0015,228 MW15,233 MW
15 Sept, 07:0015,815 MW15,699 MW
15 Sept, 08:0015,357 MW15,409 MW
15 Sept, 09:0014,693 MW14,838 MW
15 Sept, 10:0014,492 MW14,550 MW
15 Sept, 11:0014,578 MW14,587 MW
15 Sept, 12:0014,824 MW14,776 MW
15 Sept, 13:0015,231 MW15,150 MW
15 Sept, 14:0015,651 MW15,577 MW
15 Sept, 15:0016,305 MW16,187 MW
15 Sept, 16:0017,201 MW17,019 MW
15 Sept, 17:0018,344 MW17,877 MW
15 Sept, 18:0018,751 MW18,274 MW
15 Sept, 19:0018,818 MW18,593 MW
15 Sept, 20:0018,356 MW18,185 MW
15 Sept, 21:0017,484 MW17,285 MW
15 Sept, 22:0016,603 MW16,281 MW
15 Sept, 23:0015,556 MW15,326 MW
16 Sept, 00:0014,812 MW14,422 MW
16 Sept, 01:0014,266 MW13,851 MW
16 Sept, 02:0013,889 MW13,483 MW
16 Sept, 03:0013,697 MW13,298 MW
16 Sept, 04:0013,796 MW13,378 MW
16 Sept, 05:0014,460 MW14,023 MW
16 Sept, 06:0015,745 MW15,273 MW
16 Sept, 07:0016,638 MW16,090 MW
16 Sept, 08:0017,053 MW16,328 MW
16 Sept, 09:0017,216 MW16,261 MW
16 Sept, 10:0016,831 MW16,475 MW
16 Sept, 11:0016,637 MW16,872 MW
16 Sept, 12:0016,890 MW17,303 MW
16 Sept, 13:0017,399 MW17,881 MW
16 Sept, 14:0018,070 MW18,303 MW
16 Sept, 15:0018,759 MW18,773 MW
16 Sept, 16:0019,467 MW19,349 MW
16 Sept, 17:0020,299 MW19,939 MW
16 Sept, 18:0020,463 MW20,131 MW
16 Sept, 19:0020,620 MW20,347 MW
16 Sept, 20:0020,183 MW19,902 MW
16 Sept, 21:0019,389 MW18,975 MW
16 Sept, 22:0018,435 MW17,857 MW
16 Sept, 23:0017,380 MW16,750 MW
17 Sept, 00:0016,579 MW15,830 MW
17 Sept, 01:0015,854 MW15,156 MW
17 Sept, 02:0015,375 MW14,686 MW
17 Sept, 03:0015,110 MW14,419 MW
17 Sept, 04:0015,169 MW14,465 MW
17 Sept, 05:0015,825 MW15,101 MW
17 Sept, 06:0017,200 MW16,391 MW
17 Sept, 07:0018,235 MW17,310 MW
17 Sept, 08:0018,826 MW17,718 MW
17 Sept, 09:0019,112 MW17,868 MW
17 Sept, 10:0019,349 MW18,241 MW
17 Sept, 11:0019,854 MW18,681 MW
17 Sept, 12:0020,293 MW19,116 MW
17 Sept, 13:0020,995 MW19,634 MW
17 Sept, 14:0021,566 MW19,977 MW
17 Sept, 15:0022,035 MW20,354 MW
17 Sept, 16:0022,477 MW20,779 MW
17 Sept, 17:0022,571 MW21,224 MW
17 Sept, 18:0022,378 MW21,313 MW
17 Sept, 19:0022,449 MW21,344 MW
17 Sept, 20:0021,874 MW20,812 MW
17 Sept, 21:0020,962 MW19,845 MW
17 Sept, 22:0019,915 MW18,699 MW
17 Sept, 23:0018,741 MW17,519 MW
18 Sept, 00:0017,713 MW16,873 MW
18 Sept, 01:0016,941 MW16,117 MW
18 Sept, 02:0016,425 MW15,574 MW
18 Sept, 03:0016,143 MW15,227 MW
18 Sept, 04:0016,155 MW15,183 MW
18 Sept, 05:0016,773 MW15,696 MW
18 Sept, 06:0018,025 MW16,862 MW
18 Sept, 07:0018,668 MW17,419 MW
18 Sept, 08:0018,464 MW17,238 MW
18 Sept, 09:0018,047 MW16,744 MW
18 Sept, 10:0017,811 MW16,524 MW
18 Sept, 11:0017,910 MW16,523 MW
18 Sept, 12:0018,282 MW16,726 MW
18 Sept, 13:0018,705 MW17,193 MW
18 Sept, 14:0019,179 MW17,636 MW
18 Sept, 15:0019,748 MW18,222 MW
18 Sept, 16:0020,414 MW18,991 MW
18 Sept, 17:0021,181 MW19,631 MW
18 Sept, 18:0021,230 MW19,710 MW
18 Sept, 19:0020,839 MW19,613 MW
18 Sept, 20:0020,039 MW18,947 MW
18 Sept, 21:0019,078 MW18,042 MW
18 Sept, 22:0017,992 MW17,088 MW
18 Sept, 23:0016,870 MW16,071 MW
19 Sept, 00:0015,846 MW15,331 MW
19 Sept, 01:0015,087 MW14,566 MW
19 Sept, 02:0014,506 MW14,020 MW
19 Sept, 03:0014,103 MW13,671 MW
19 Sept, 04:0013,884 MW13,504 MW
19 Sept, 05:0013,920 MW13,578 MW
19 Sept, 06:0014,229 MW13,907 MW
19 Sept, 07:0014,320 MW14,000 MW
19 Sept, 08:0013,913 MW13,810 MW
19 Sept, 09:0013,438 MW13,341 MW
19 Sept, 10:0013,216 MW12,954 MW
19 Sept, 11:0013,233 MW12,838 MW
19 Sept, 12:0013,452 MW12,895 MW
19 Sept, 13:0013,876 MW13,126 MW
19 Sept, 14:0014,479 MW13,478 MW
19 Sept, 15:0015,206 MW14,084 MW
19 Sept, 16:0015,845 MW14,943 MW
19 Sept, 17:0016,361 MW15,796 MW
19 Sept, 18:0016,754 MW16,407 MW
19 Sept, 19:0017,046 MW16,822 MW
19 Sept, 20:0016,737 MW16,552 MW
19 Sept, 21:0016,251 MW15,997 MW
19 Sept, 22:0015,611 MW15,342 MW
19 Sept, 23:0014,902 MW14,614 MW
20 Sept, 00:0014,348 MW14,008 MW
20 Sept, 01:0013,809 MW13,493 MW
20 Sept, 02:0013,416 MW13,127 MW
20 Sept, 03:0013,213 MW12,928 MW
20 Sept, 04:0013,130 MW12,850 MW
20 Sept, 05:0013,262 MW12,945 MW
20 Sept, 06:0013,612 MW13,233 MW
20 Sept, 07:0014,039 MW13,638 MW
20 Sept, 08:0014,736 MW14,157 MW
20 Sept, 09:0015,375 MW14,550 MW
20 Sept, 10:0015,763 MW14,892 MW
20 Sept, 11:0015,996 MW15,211 MW
20 Sept, 12:0016,221 MW15,486 MW
20 Sept, 13:0016,363 MW15,707 MW
20 Sept, 14:0016,429 MW15,862 MW
20 Sept, 15:0016,571 MW16,136 MW
20 Sept, 16:0016,982 MW16,585 MW
20 Sept, 17:0017,477 MW17,084 MW
20 Sept, 18:0017,761 MW17,358 MW
20 Sept, 19:0017,928 MW17,735 MW
20 Sept, 20:0017,605 MW17,394 MW
20 Sept, 21:0016,982 MW16,655 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.