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

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

The day-ahead demand forecast for PSEI was off by 31.8% on average (mean absolute percentage error) over 719 hours from 21 August to 20 September 2026, and 3% of hours landed within 5% of the reading. Its bias was -31.7%: it ran low on average, an under forecast. The largest miss was 1,671 MW (63.7%) too low at 18 Sept 2026, 10:00 PDT (UTC-07:00). Dates and times are local (America/Los_Angeles).

Key Facts

  • The day-ahead demand forecast for PSEI was off by 31.8% on average (mean absolute percentage error) over 719 hours from 21 August to 20 September 2026, and 3% of hours landed within 5% of the reading. Its bias was -31.7%: it ran low on average, an under forecast. The largest miss was 1,671 MW (63.7%) too low at 18 Sept 2026, 10:00 PDT (UTC-07:00).
  • Across 53 US grids ranked by average error over their own latest 30 day windows, PSEI came 52 (1 is the smallest error).
  • On average the forecast differed from reported demand by 780 MW, against average demand of 2,437 MW.
  • The forecast was above reported demand in 1% of compared hours.

Forecast Error at a Glance

719 hours from 21 August to 20 September 2026
Average error31.8%
Bias-31.7%
Hours within 5%3%
Worst miss1,671 MW

Average error is the mean absolute percentage gap between the forecast and reported demand. Bias is the signed mean (-779 MW per hour on average): the forecast ran low on average, an under forecast. The worst miss was 1,671 MW (63.7%) too low at 18 Sept 2026, 10:00 PDT (UTC-07:00): forecast 954 MW, reported 2,625 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)
PSEI day-ahead demand forecast and reported demand by hour Hourly reported demand and the day-ahead forecast for PSEI over the last 7 days of the window, to 20 Sept 2026, 18:00 PDT (UTC-07:00). Gaps are hours with a missing, zero or implausible report. 0 750 1,500 2,250 3,000 13 Sept, 19:0014 Sept, 19:0015 Sept, 19:0016 Sept, 19:0017 Sept, 19:0018 Sept, 19:0019 Sept, 19:00
Hourly reported demand and the day-ahead forecast for PSEI over the last 7 days of the window, to 20 Sept 2026, 18:00 PDT (UTC-07:00). Gaps are hours with a missing, zero or implausible report.
Data to 2026-09-20
PSEI day-ahead demand forecast and reported demand by hour
Local hourReported demandDay-ahead forecast
13 Sept, 19:002,751 MW1,712 MW
13 Sept, 20:002,727 MW1,420 MW
13 Sept, 21:002,574 MW1,468 MW
13 Sept, 22:002,371 MW1,597 MW
13 Sept, 23:002,172 MW1,545 MW
14 Sept, 00:002,034 MW1,439 MW
14 Sept, 01:001,936 MW1,388 MW
14 Sept, 02:001,892 MW1,376 MW
14 Sept, 03:001,874 MW1,434 MW
14 Sept, 04:001,937 MW1,381 MW
14 Sept, 05:002,109 MW1,530 MW
14 Sept, 06:002,379 MW1,686 MW
14 Sept, 07:002,549 MW1,688 MW
14 Sept, 08:002,608 MW1,671 MW
14 Sept, 09:002,635 MW1,600 MW
14 Sept, 10:002,651 MW1,403 MW
14 Sept, 11:002,661 MW1,403 MW
14 Sept, 12:002,670 MW1,434 MW
14 Sept, 13:002,655 MW1,413 MW
14 Sept, 14:002,626 MW1,480 MW
14 Sept, 15:002,632 MW1,462 MW
14 Sept, 16:002,684 MW1,694 MW
14 Sept, 17:002,756 MW1,834 MW
14 Sept, 18:002,783 MW1,915 MW
14 Sept, 19:002,813 MW1,976 MW
14 Sept, 20:002,779 MW2,028 MW
14 Sept, 21:002,615 MW1,868 MW
14 Sept, 22:002,400 MW1,813 MW
14 Sept, 23:002,200 MW1,745 MW
15 Sept, 00:002,068 MW1,355 MW
15 Sept, 01:001,962 MW1,295 MW
15 Sept, 02:001,908 MW1,269 MW
15 Sept, 03:001,892 MW1,246 MW
15 Sept, 04:001,956 MW1,222 MW
15 Sept, 05:002,123 MW1,152 MW
15 Sept, 06:002,399 MW1,261 MW
15 Sept, 07:002,565 MW1,333 MW
15 Sept, 08:002,624 MW1,279 MW
15 Sept, 09:002,645 MW1,286 MW
15 Sept, 10:002,646 MW1,353 MW
15 Sept, 11:002,624 MW1,336 MW
15 Sept, 12:002,617 MW1,351 MW
15 Sept, 13:002,589 MW1,455 MW
15 Sept, 14:002,572 MW1,536 MW
15 Sept, 15:002,591 MW1,554 MW
15 Sept, 16:002,644 MW1,539 MW
15 Sept, 17:002,720 MW1,716 MW
15 Sept, 18:002,753 MW1,916 MW
15 Sept, 19:002,794 MW2,050 MW
15 Sept, 20:002,805 MW2,107 MW
15 Sept, 21:002,645 MW2,107 MW
15 Sept, 22:002,420 MW2,015 MW
15 Sept, 23:002,218 MW1,809 MW
16 Sept, 00:002,072 MW1,629 MW
16 Sept, 01:001,974 MW1,419 MW
16 Sept, 02:001,918 MW1,402 MW
16 Sept, 03:001,910 MW1,462 MW
16 Sept, 04:001,983 MW1,368 MW
16 Sept, 05:002,166 MW1,683 MW
16 Sept, 06:002,442 MW1,737 MW
16 Sept, 07:002,613 MW1,730 MW
16 Sept, 08:002,640 MW1,533 MW
16 Sept, 09:002,611 MW1,503 MW
16 Sept, 10:002,586 MW1,573 MW
16 Sept, 11:002,572 MW1,609 MW
16 Sept, 12:002,594 MW1,501 MW
16 Sept, 13:002,600 MW1,500 MW
16 Sept, 14:002,628 MW1,524 MW
16 Sept, 15:002,681 MW1,625 MW
16 Sept, 16:002,772 MW1,824 MW
16 Sept, 17:002,857 MW1,774 MW
16 Sept, 18:002,866 MW1,964 MW
16 Sept, 19:002,884 MW1,953 MW
16 Sept, 20:002,858 MW2,027 MW
16 Sept, 21:002,692 MW1,995 MW
16 Sept, 22:002,460 MW1,836 MW
16 Sept, 23:002,243 MW1,797 MW
17 Sept, 00:002,088 MW1,413 MW
17 Sept, 01:001,973 MW1,348 MW
17 Sept, 02:001,900 MW1,231 MW
17 Sept, 03:001,887 MW1,265 MW
17 Sept, 04:001,945 MW1,297 MW
17 Sept, 05:002,107 MW1,321 MW
17 Sept, 06:002,379 MW1,559 MW
17 Sept, 07:002,553 MW1,719 MW
17 Sept, 08:002,598 MW1,557 MW
17 Sept, 09:002,589 MW1,447 MW
17 Sept, 10:002,590 MW1,414 MW
17 Sept, 11:002,589 MW1,418 MW
17 Sept, 12:002,624 MW1,375 MW
17 Sept, 13:002,639 MW1,434 MW
17 Sept, 14:002,688 MW1,502 MW
17 Sept, 15:002,748 MW1,447 MW
17 Sept, 16:002,843 MW1,436 MW
17 Sept, 17:002,919 MW1,544 MW
17 Sept, 18:002,895 MW1,708 MW
17 Sept, 19:002,900 MW1,790 MW
17 Sept, 20:002,860 MW1,817 MW
17 Sept, 21:002,698 MW1,813 MW
17 Sept, 22:002,465 MW1,815 MW
17 Sept, 23:002,261 MW1,665 MW
18 Sept, 00:002,107 MW1,426 MW
18 Sept, 01:001,971 MW1,289 MW
18 Sept, 02:001,915 MW1,208 MW
18 Sept, 03:001,884 MW1,148 MW
18 Sept, 04:001,937 MW1,070 MW
18 Sept, 05:002,069 MW1,157 MW
18 Sept, 06:002,327 MW1,134 MW
18 Sept, 07:002,503 MW1,098 MW
18 Sept, 08:002,586 MW1,055 MW
18 Sept, 09:002,621 MW982 MW
18 Sept, 10:002,625 MW954 MW
18 Sept, 11:002,609 MW972 MW
18 Sept, 12:002,579 MW986 MW
18 Sept, 13:002,553 MW986 MW
18 Sept, 14:002,557 MW1,065 MW
18 Sept, 15:002,599 MW1,097 MW
18 Sept, 16:002,681 MW1,381 MW
18 Sept, 17:002,747 MW1,462 MW
18 Sept, 18:002,724 MW1,646 MW
18 Sept, 19:002,727 MW1,658 MW
18 Sept, 20:002,695 MW1,648 MW
18 Sept, 21:002,563 MW1,574 MW
18 Sept, 22:002,409 MW1,467 MW
18 Sept, 23:002,224 MW1,318 MW
19 Sept, 00:002,091 MW1,276 MW
19 Sept, 01:001,970 MW1,444 MW
19 Sept, 02:001,902 MW1,369 MW
19 Sept, 03:001,874 MW1,273 MW
19 Sept, 04:001,884 MW1,273 MW
19 Sept, 05:001,946 MW1,313 MW
19 Sept, 06:002,063 MW1,233 MW
19 Sept, 07:002,201 MW1,188 MW
19 Sept, 08:002,339 MW1,244 MW
19 Sept, 09:002,440 MW1,247 MW
19 Sept, 10:002,486 MW1,227 MW
19 Sept, 11:002,490 MW1,160 MW
19 Sept, 12:002,481 MW1,154 MW
19 Sept, 13:002,441 MW1,116 MW
19 Sept, 14:002,395 MW1,178 MW
19 Sept, 15:002,390 MW1,165 MW
19 Sept, 16:002,452 MW1,364 MW
19 Sept, 17:002,526 MW1,376 MW
19 Sept, 18:002,566 MW1,439 MW
19 Sept, 19:002,610 MW1,452 MW
19 Sept, 20:002,603 MW1,443 MW
19 Sept, 21:002,491 MW1,216 MW
19 Sept, 22:002,356 MW1,463 MW
19 Sept, 23:002,207 MW1,245 MW
20 Sept, 00:002,075 MW1,147 MW
20 Sept, 01:001,969 MW1,052 MW
20 Sept, 02:001,910 MW986 MW
20 Sept, 03:001,879 MW967 MW
20 Sept, 04:001,895 MW1,022 MW
20 Sept, 05:001,952 MW1,017 MW
20 Sept, 06:002,062 MW1,045 MW
20 Sept, 07:002,191 MW1,073 MW
20 Sept, 08:002,330 MW1,102 MW
20 Sept, 09:002,425 MW1,055 MW
20 Sept, 10:002,455 MW1,020 MW
20 Sept, 11:002,456 MW1,031 MW
20 Sept, 12:002,436 MW1,036 MW
20 Sept, 13:002,434 MW1,026 MW
20 Sept, 14:002,437 MW1,064 MW
20 Sept, 15:002,509 MW1,089 MW
20 Sept, 16:002,602 MW1,154 MW
20 Sept, 17:002,718 MW1,409 MW
20 Sept, 18:002,757 MW1,365 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.