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

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

The day-ahead demand forecast for SPP was off by 7.2% on average (mean absolute percentage error) over 688 hours from 21 August to 20 September 2026, and 46% of hours landed within 5% of the reading. Its bias was +7.0%: it ran high on average, an over forecast. The largest miss was 15,947 MW (39.7%) too high at 14 Sept 2026, 17:00 CDT (UTC-05:00). Dates and times are local (America/Chicago).

Key Facts

  • The day-ahead demand forecast for SPP was off by 7.2% on average (mean absolute percentage error) over 688 hours from 21 August to 20 September 2026, and 46% of hours landed within 5% of the reading. Its bias was +7.0%: it ran high on average, an over forecast. The largest miss was 15,947 MW (39.7%) too high at 14 Sept 2026, 17:00 CDT (UTC-05:00).
  • Across 53 US grids ranked by average error over their own latest 30 day windows, SPP came 37 (1 is the smallest error).
  • On average the forecast differed from reported demand by 2,951 MW, against average demand of 42,174 MW.
  • The forecast was above reported demand in 90% of compared hours.

Forecast Error at a Glance

688 hours from 21 August to 20 September 2026
Average error7.2%
Bias+7.0%
Hours within 5%46%
Worst miss15,947 MW

Average error is the mean absolute percentage gap between the forecast and reported demand. Bias is the signed mean (+2,872 MW per hour on average): the forecast ran high on average, an over forecast. The worst miss was 15,947 MW (39.7%) too high at 14 Sept 2026, 17:00 CDT (UTC-05:00): forecast 56,124 MW, reported 40,177 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, 20:00 CDT (UTC-05:00)
SPP day-ahead demand forecast and reported demand by hour Hourly reported demand and the day-ahead forecast for SPP over the last 7 days of the window, to 20 Sept 2026, 20:00 CDT (UTC-05:00). Gaps are hours with a missing, zero or implausible report. 0 15,000 30,000 45,000 60,000 13 Sept, 21:0014 Sept, 21:0015 Sept, 21:0016 Sept, 21:0017 Sept, 21:0018 Sept, 21:0019 Sept, 21:00
Hourly reported demand and the day-ahead forecast for SPP over the last 7 days of the window, to 20 Sept 2026, 20:00 CDT (UTC-05:00). Gaps are hours with a missing, zero or implausible report.
Data to 2026-09-20
SPP day-ahead demand forecast and reported demand by hour
Local hourReported demandDay-ahead forecast
13 Sept, 21:0040,875 MW46,130 MW
13 Sept, 22:0038,665 MW43,968 MW
13 Sept, 23:0036,531 MW41,837 MW
14 Sept, 00:0034,926 MW39,208 MW
14 Sept, 01:0033,726 MW37,931 MW
14 Sept, 02:0032,954 MW36,866 MW
14 Sept, 03:0032,624 MW36,280 MW
14 Sept, 04:0032,747 MW36,339 MW
14 Sept, 05:0033,551 MW37,060 MW
14 Sept, 06:0035,111 MW38,424 MW
14 Sept, 07:0036,059 MW39,444 MW
14 Sept, 08:0037,150 MW41,264 MW
14 Sept, 09:0038,962 MW43,627 MW
14 Sept, 10:0040,166 MW46,071 MW
14 Sept, 11:0040,177 MW48,780 MW
14 Sept, 12:0040,177 MW51,274 MW
14 Sept, 13:0040,177 MW53,069 MW
14 Sept, 14:0040,177 MW54,626 MW
14 Sept, 15:0040,177 MW55,543 MW
14 Sept, 16:0040,177 MW56,095 MW
14 Sept, 17:0040,177 MW56,124 MW
14 Sept, 18:0040,177 MW55,411 MW
14 Sept, 19:0040,177 MW53,931 MW
14 Sept, 20:0040,177 MW52,248 MW
14 Sept, 21:0040,177 MW50,309 MW
14 Sept, 22:0040,177 MW47,847 MW
14 Sept, 23:0040,177 MW45,365 MW
15 Sept, 00:0036,476 MW38,534 MW
15 Sept, 01:0036,218 MW37,061 MW
15 Sept, 02:0035,961 MW35,965 MW
15 Sept, 03:0035,704 MW35,161 MW
15 Sept, 04:0035,447 MW34,830 MW
15 Sept, 05:0035,640 MW35,463 MW
15 Sept, 06:0036,813 MW36,628 MW
15 Sept, 07:0037,515 MW37,417 MW
15 Sept, 08:0038,486 MW38,579 MW
15 Sept, 09:0040,406 MW40,318 MW
15 Sept, 10:0042,545 MW42,369 MW
15 Sept, 11:0044,784 MW44,585 MW
15 Sept, 12:0046,761 MW46,475 MW
15 Sept, 13:0048,315 MW47,899 MW
15 Sept, 14:0049,242 MW48,689 MW
15 Sept, 15:0049,715 MW49,041 MW
15 Sept, 16:0049,677 MW49,011 MW
15 Sept, 17:0048,978 MW48,485 MW
15 Sept, 18:0047,453 MW47,577 MW
15 Sept, 19:0045,617 MW45,999 MW
15 Sept, 20:0043,904 MW44,567 MW
15 Sept, 21:0041,904 MW42,917 MW
15 Sept, 22:0039,538 MW40,689 MW
15 Sept, 23:0037,167 MW38,443 MW
16 Sept, 00:0035,445 MW36,687 MW
16 Sept, 01:0034,270 MW35,294 MW
16 Sept, 02:0033,380 MW34,307 MW
16 Sept, 03:0032,875 MW33,634 MW
16 Sept, 04:0032,773 MW33,456 MW
16 Sept, 05:0033,447 MW34,040 MW
16 Sept, 06:0034,952 MW35,251 MW
16 Sept, 07:0035,920 MW36,055 MW
16 Sept, 08:0036,804 MW37,260 MW
16 Sept, 09:0038,369 MW38,903 MW
16 Sept, 10:0040,292 MW40,935 MW
16 Sept, 11:0042,339 MW43,140 MW
16 Sept, 12:0044,355 MW45,224 MW
16 Sept, 13:0046,123 MW46,942 MW
16 Sept, 14:0047,293 MW48,027 MW
16 Sept, 15:0048,135 MW48,961 MW
16 Sept, 16:0048,373 MW49,481 MW
16 Sept, 17:0048,210 MW49,378 MW
16 Sept, 18:0047,457 MW48,547 MW
16 Sept, 19:0046,014 MW47,112 MW
16 Sept, 20:0044,773 MW45,632 MW
16 Sept, 21:0042,796 MW43,927 MW
16 Sept, 22:0040,500 MW41,497 MW
16 Sept, 23:0038,092 MW39,087 MW
17 Sept, 00:0036,236 MW36,827 MW
17 Sept, 01:0034,842 MW35,418 MW
17 Sept, 02:0033,838 MW34,414 MW
17 Sept, 03:0033,194 MW33,697 MW
17 Sept, 04:0032,921 MW33,564 MW
17 Sept, 05:0033,347 MW34,134 MW
17 Sept, 06:0034,837 MW35,392 MW
17 Sept, 07:0036,166 MW36,306 MW
17 Sept, 08:0037,208 MW37,719 MW
17 Sept, 09:0039,224 MW39,861 MW
17 Sept, 10:0041,655 MW42,134 MW
17 Sept, 11:0044,170 MW44,539 MW
17 Sept, 12:0046,429 MW46,738 MW
17 Sept, 13:0048,449 MW48,521 MW
17 Sept, 14:0049,775 MW49,600 MW
17 Sept, 15:0050,776 MW50,373 MW
17 Sept, 16:0051,058 MW50,692 MW
17 Sept, 17:0050,679 MW50,466 MW
17 Sept, 18:0049,468 MW49,374 MW
17 Sept, 19:0047,799 MW47,832 MW
17 Sept, 20:0046,278 MW46,307 MW
17 Sept, 21:0044,106 MW44,417 MW
17 Sept, 22:0041,553 MW42,053 MW
17 Sept, 23:0039,063 MW39,786 MW
18 Sept, 00:0037,153 MW38,013 MW
18 Sept, 01:0035,682 MW36,536 MW
18 Sept, 02:0034,576 MW35,378 MW
18 Sept, 03:0033,757 MW34,636 MW
18 Sept, 04:0033,568 MW34,336 MW
18 Sept, 05:0034,199 MW34,853 MW
18 Sept, 06:0035,478 MW36,045 MW
18 Sept, 07:0036,273 MW36,950 MW
18 Sept, 08:0037,590 MW38,436 MW
18 Sept, 09:0039,724 MW40,671 MW
18 Sept, 10:0042,516 MW43,151 MW
18 Sept, 11:0045,204 MW45,802 MW
18 Sept, 12:0047,583 MW47,970 MW
18 Sept, 13:0049,556 MW49,874 MW
18 Sept, 14:0050,726 MW51,095 MW
18 Sept, 15:0051,425 MW51,897 MW
18 Sept, 16:0051,644 MW52,105 MW
18 Sept, 17:0051,037 MW51,725 MW
18 Sept, 18:0049,393 MW50,470 MW
18 Sept, 19:0047,342 MW48,566 MW
18 Sept, 20:0045,426 MW46,814 MW
18 Sept, 21:0043,344 MW44,856 MW
18 Sept, 22:0041,221 MW42,648 MW
18 Sept, 23:0038,953 MW40,336 MW
19 Sept, 00:0036,866 MW41,591 MW
19 Sept, 01:0035,411 MW39,918 MW
19 Sept, 02:0034,219 MW38,721 MW
19 Sept, 03:0033,365 MW37,737 MW
19 Sept, 04:0032,838 MW37,214 MW
19 Sept, 05:0032,637 MW37,207 MW
19 Sept, 06:0032,855 MW37,318 MW
19 Sept, 07:0033,151 MW37,678 MW
19 Sept, 08:0034,516 MW39,517 MW
19 Sept, 09:0036,757 MW41,914 MW
19 Sept, 10:0039,160 MW44,326 MW
19 Sept, 11:0041,493 MW47,019 MW
19 Sept, 12:0043,607 MW49,286 MW
19 Sept, 13:0045,464 MW50,930 MW
19 Sept, 14:0046,750 MW52,010 MW
19 Sept, 15:0047,791 MW52,932 MW
19 Sept, 16:0048,255 MW53,280 MW
19 Sept, 17:0047,805 MW53,052 MW
19 Sept, 18:0046,233 MW51,758 MW
19 Sept, 19:0044,053 MW50,054 MW
19 Sept, 20:0042,062 MW48,242 MW
19 Sept, 21:0040,055 MW46,384 MW
19 Sept, 22:0038,120 MW44,433 MW
19 Sept, 23:0036,147 MW42,234 MW
20 Sept, 00:0034,472 MW39,066 MW
20 Sept, 01:0033,053 MW37,603 MW
20 Sept, 02:0031,870 MW36,423 MW
20 Sept, 03:0031,184 MW35,626 MW
20 Sept, 04:0030,667 MW35,130 MW
20 Sept, 05:0030,599 MW34,959 MW
20 Sept, 06:0030,747 MW34,986 MW
20 Sept, 07:0030,998 MW35,156 MW
20 Sept, 08:0032,111 MW36,331 MW
20 Sept, 09:0033,783 MW38,131 MW
20 Sept, 10:0035,614 MW39,941 MW
20 Sept, 11:0037,637 MW41,708 MW
20 Sept, 12:0039,399 MW43,412 MW
20 Sept, 13:0040,655 MW44,628 MW
20 Sept, 14:0041,188 MW45,592 MW
20 Sept, 15:0041,616 MW46,355 MW
20 Sept, 16:0041,960 MW46,625 MW
20 Sept, 17:0041,683 MW46,776 MW
20 Sept, 18:0040,668 MW45,946 MW
20 Sept, 19:0039,748 MW44,501 MW
20 Sept, 20:0038,725 MW43,211 MW

Assumptions

  • Only hours with both a forecast and a positive demand reading count (688 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.