PJM Demand Forecast Accuracy: Error, Bias and Worst Miss, 21 August to 20 September 2026
The day-ahead demand forecast for PJM was off by 4.0% on average (mean absolute percentage error) over 719 hours from 21 August to 20 September 2026, and 64% 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 12,035 MW (10.3%) too high at 31 Aug 2026, 11:00 EDT (UTC-04:00). Dates and times are local (America/New_York).
Key Facts
- The day-ahead demand forecast for PJM was off by 4.0% on average (mean absolute percentage error) over 719 hours from 21 August to 20 September 2026, and 64% 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 12,035 MW (10.3%) too high at 31 Aug 2026, 11:00 EDT (UTC-04:00).
- Across 53 US grids ranked by average error over their own latest 30 day windows, PJM came 26 (1 is the smallest error).
- On average the forecast differed from reported demand by 4,159 MW, against average demand of 105.9 GW.
- The forecast was above reported demand in 36% of compared hours.
Forecast Error at a Glance
719 hours from 21 August to 20 September 2026Average error4.0%
Bias-2.0%
Hours within 5%64%
Worst miss12,035 MW
Average error is the mean absolute percentage gap between the forecast and reported demand. Bias is the signed mean (-1,943 MW per hour on average): the forecast ran low on average, an under forecast. The worst miss was 12,035 MW (10.3%) too high at 31 Aug 2026, 11:00 EDT (UTC-04:00): forecast 128.7 GW, reported 116.6 GW.
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)Data to 2026-09-20
| Local hour | Reported demand | Day-ahead forecast |
|---|---|---|
| 13 Sept, 22:00 | 103.1 GW | 93,706 MW |
| 13 Sept, 23:00 | 97,804 MW | 87,742 MW |
| 14 Sept, 00:00 | 93,207 MW | 85,757 MW |
| 14 Sept, 01:00 | 90,170 MW | 83,167 MW |
| 14 Sept, 02:00 | 88,090 MW | 81,680 MW |
| 14 Sept, 03:00 | 86,595 MW | 81,905 MW |
| 14 Sept, 04:00 | 86,844 MW | 85,043 MW |
| 14 Sept, 05:00 | 88,669 MW | 90,365 MW |
| 14 Sept, 06:00 | 91,925 MW | 93,953 MW |
| 14 Sept, 07:00 | 94,942 MW | 95,669 MW |
| 14 Sept, 08:00 | 96,631 MW | 97,206 MW |
| 14 Sept, 09:00 | 98,995 MW | 99,167 MW |
| 14 Sept, 10:00 | 101.2 GW | 101.0 GW |
| 14 Sept, 11:00 | 102.5 GW | 102.9 GW |
| 14 Sept, 12:00 | 103.1 GW | 104.9 GW |
| 14 Sept, 13:00 | 104.6 GW | 106.3 GW |
| 14 Sept, 14:00 | 106.0 GW | 107.1 GW |
| 14 Sept, 15:00 | 107.7 GW | 107.9 GW |
| 14 Sept, 16:00 | 109.7 GW | 108.3 GW |
| 14 Sept, 17:00 | 110.8 GW | 107.0 GW |
| 14 Sept, 18:00 | 109.3 GW | 104.8 GW |
| 14 Sept, 19:00 | 106.5 GW | 102.8 GW |
| 14 Sept, 20:00 | 104.1 GW | 98,631 MW |
| 14 Sept, 21:00 | 98,911 MW | 92,657 MW |
| 14 Sept, 22:00 | 93,044 MW | 86,671 MW |
| 14 Sept, 23:00 | 88,619 MW | 82,466 MW |
| 15 Sept, 00:00 | 84,896 MW | 79,441 MW |
| 15 Sept, 01:00 | 81,780 MW | 77,331 MW |
| 15 Sept, 02:00 | 79,763 MW | 76,124 MW |
| 15 Sept, 03:00 | 78,739 MW | 76,613 MW |
| 15 Sept, 04:00 | 79,151 MW | 79,522 MW |
| 15 Sept, 05:00 | 82,175 MW | 84,676 MW |
| 15 Sept, 06:00 | 85,815 MW | 87,974 MW |
| 15 Sept, 07:00 | 88,051 MW | 89,714 MW |
| 15 Sept, 08:00 | 90,051 MW | 91,005 MW |
| 15 Sept, 09:00 | 92,063 MW | 93,094 MW |
| 15 Sept, 10:00 | 93,716 MW | 95,462 MW |
| 15 Sept, 11:00 | 94,490 MW | 98,392 MW |
| 15 Sept, 12:00 | 96,665 MW | 101.7 GW |
| 15 Sept, 13:00 | 100.8 GW | 104.9 GW |
| 15 Sept, 14:00 | 105.2 GW | 108.0 GW |
| 15 Sept, 15:00 | 109.9 GW | 111.4 GW |
| 15 Sept, 16:00 | 114.7 GW | 113.6 GW |
| 15 Sept, 17:00 | 117.7 GW | 113.5 GW |
| 15 Sept, 18:00 | 117.3 GW | 111.5 GW |
| 15 Sept, 19:00 | 115.0 GW | 108.8 GW |
| 15 Sept, 20:00 | 112.7 GW | 104.1 GW |
| 15 Sept, 21:00 | 107.4 GW | 97,753 MW |
| 15 Sept, 22:00 | 100.7 GW | 91,237 MW |
| 15 Sept, 23:00 | 95,161 MW | 86,196 MW |
| 16 Sept, 00:00 | 91,088 MW | 84,261 MW |
| 16 Sept, 01:00 | 88,457 MW | 81,394 MW |
| 16 Sept, 02:00 | 86,158 MW | 79,728 MW |
| 16 Sept, 03:00 | 84,637 MW | 79,903 MW |
| 16 Sept, 04:00 | 84,698 MW | 82,377 MW |
| 16 Sept, 05:00 | 87,472 MW | 87,361 MW |
| 16 Sept, 06:00 | 91,811 MW | 91,117 MW |
| 16 Sept, 07:00 | 95,269 MW | 93,670 MW |
| 16 Sept, 08:00 | 98,425 MW | 96,347 MW |
| 16 Sept, 09:00 | 100.3 GW | 99,984 MW |
| 16 Sept, 10:00 | 102.8 GW | 103.8 GW |
| 16 Sept, 11:00 | 105.3 GW | 108.2 GW |
| 16 Sept, 12:00 | 108.5 GW | 112.4 GW |
| 16 Sept, 13:00 | 113.6 GW | 116.0 GW |
| 16 Sept, 14:00 | 118.2 GW | 119.3 GW |
| 16 Sept, 15:00 | 122.7 GW | 122.3 GW |
| 16 Sept, 16:00 | 126.2 GW | 123.9 GW |
| 16 Sept, 17:00 | 127.7 GW | 122.6 GW |
| 16 Sept, 18:00 | 125.8 GW | 119.5 GW |
| 16 Sept, 19:00 | 123.0 GW | 116.2 GW |
| 16 Sept, 20:00 | 120.0 GW | 111.3 GW |
| 16 Sept, 21:00 | 114.7 GW | 104.3 GW |
| 16 Sept, 22:00 | 107.8 GW | 97,262 MW |
| 16 Sept, 23:00 | 101.9 GW | 91,988 MW |
| 17 Sept, 00:00 | 98,242 MW | 88,886 MW |
| 17 Sept, 01:00 | 94,231 MW | 85,912 MW |
| 17 Sept, 02:00 | 91,283 MW | 84,228 MW |
| 17 Sept, 03:00 | 89,638 MW | 84,424 MW |
| 17 Sept, 04:00 | 89,872 MW | 87,192 MW |
| 17 Sept, 05:00 | 92,663 MW | 92,421 MW |
| 17 Sept, 06:00 | 97,827 MW | 96,364 MW |
| 17 Sept, 07:00 | 101.6 GW | 99,525 MW |
| 17 Sept, 08:00 | 105.2 GW | 102.8 GW |
| 17 Sept, 09:00 | 107.9 GW | 107.0 GW |
| 17 Sept, 10:00 | 111.3 GW | 111.6 GW |
| 17 Sept, 11:00 | 114.3 GW | 116.3 GW |
| 17 Sept, 12:00 | 118.9 GW | 120.9 GW |
| 17 Sept, 13:00 | 123.4 GW | 124.5 GW |
| 17 Sept, 14:00 | 124.5 GW | 127.4 GW |
| 17 Sept, 15:00 | 124.6 GW | 129.8 GW |
| 17 Sept, 16:00 | 126.0 GW | 130.9 GW |
| 17 Sept, 17:00 | 126.4 GW | 129.2 GW |
| 17 Sept, 18:00 | 124.2 GW | 125.5 GW |
| 17 Sept, 19:00 | 122.5 GW | 121.9 GW |
| 17 Sept, 20:00 | 119.8 GW | 116.6 GW |
| 17 Sept, 21:00 | 114.7 GW | 109.4 GW |
| 17 Sept, 22:00 | 109.3 GW | 102.3 GW |
| 17 Sept, 23:00 | 104.8 GW | 96,123 MW |
| 18 Sept, 00:00 | 100.4 GW | 92,923 MW |
| 18 Sept, 01:00 | 96,809 MW | 89,729 MW |
| 18 Sept, 02:00 | 94,053 MW | 87,807 MW |
| 18 Sept, 03:00 | 92,173 MW | 87,666 MW |
| 18 Sept, 04:00 | 91,815 MW | 90,012 MW |
| 18 Sept, 05:00 | 94,532 MW | 94,782 MW |
| 18 Sept, 06:00 | 98,787 MW | 98,427 MW |
| 18 Sept, 07:00 | 102.7 GW | 101.3 GW |
| 18 Sept, 08:00 | 105.7 GW | 104.2 GW |
| 18 Sept, 09:00 | 109.1 GW | 107.5 GW |
| 18 Sept, 10:00 | 111.4 GW | 111.1 GW |
| 18 Sept, 11:00 | 113.4 GW | 114.7 GW |
| 18 Sept, 12:00 | 115.9 GW | 117.8 GW |
| 18 Sept, 13:00 | 118.0 GW | 120.1 GW |
| 18 Sept, 14:00 | 119.2 GW | 121.5 GW |
| 18 Sept, 15:00 | 120.8 GW | 122.1 GW |
| 18 Sept, 16:00 | 121.8 GW | 121.6 GW |
| 18 Sept, 17:00 | 121.4 GW | 118.6 GW |
| 18 Sept, 18:00 | 118.3 GW | 114.8 GW |
| 18 Sept, 19:00 | 114.3 GW | 111.8 GW |
| 18 Sept, 20:00 | 111.0 GW | 107.2 GW |
| 18 Sept, 21:00 | 106.4 GW | 101.4 GW |
| 18 Sept, 22:00 | 101.0 GW | 95,270 MW |
| 18 Sept, 23:00 | 95,557 MW | 90,237 MW |
| 19 Sept, 00:00 | 90,976 MW | 86,685 MW |
| 19 Sept, 01:00 | 87,970 MW | 83,611 MW |
| 19 Sept, 02:00 | 85,871 MW | 81,545 MW |
| 19 Sept, 03:00 | 83,628 MW | 80,415 MW |
| 19 Sept, 04:00 | 82,525 MW | 80,831 MW |
| 19 Sept, 05:00 | 82,840 MW | 82,254 MW |
| 19 Sept, 06:00 | 84,312 MW | 83,633 MW |
| 19 Sept, 07:00 | 85,920 MW | 86,074 MW |
| 19 Sept, 08:00 | 87,596 MW | 88,741 MW |
| 19 Sept, 09:00 | 90,406 MW | 91,383 MW |
| 19 Sept, 10:00 | 92,258 MW | 93,694 MW |
| 19 Sept, 11:00 | 94,457 MW | 96,038 MW |
| 19 Sept, 12:00 | 96,368 MW | 98,182 MW |
| 19 Sept, 13:00 | 98,943 MW | 100.3 GW |
| 19 Sept, 14:00 | 101.9 GW | 102.4 GW |
| 19 Sept, 15:00 | 103.4 GW | 104.8 GW |
| 19 Sept, 16:00 | 104.5 GW | 106.0 GW |
| 19 Sept, 17:00 | 104.8 GW | 105.5 GW |
| 19 Sept, 18:00 | 104.0 GW | 103.5 GW |
| 19 Sept, 19:00 | 103.4 GW | 101.7 GW |
| 19 Sept, 20:00 | 101.9 GW | 98,252 MW |
| 19 Sept, 21:00 | 98,731 MW | 93,500 MW |
| 19 Sept, 22:00 | 95,032 MW | 88,288 MW |
| 19 Sept, 23:00 | 91,378 MW | 85,138 MW |
| 20 Sept, 00:00 | 88,179 MW | 81,257 MW |
| 20 Sept, 01:00 | 85,757 MW | 78,813 MW |
| 20 Sept, 02:00 | 84,600 MW | 77,097 MW |
| 20 Sept, 03:00 | 83,082 MW | 76,406 MW |
| 20 Sept, 04:00 | 82,113 MW | 76,674 MW |
| 20 Sept, 05:00 | 82,151 MW | 77,757 MW |
| 20 Sept, 06:00 | 83,092 MW | 79,194 MW |
| 20 Sept, 07:00 | 84,502 MW | 82,116 MW |
| 20 Sept, 08:00 | 87,742 MW | 85,753 MW |
| 20 Sept, 09:00 | 91,210 MW | 89,479 MW |
| 20 Sept, 10:00 | 94,125 MW | 93,267 MW |
| 20 Sept, 11:00 | 95,899 MW | 96,933 MW |
| 20 Sept, 12:00 | 98,983 MW | 100.2 GW |
| 20 Sept, 13:00 | 101.9 GW | 102.9 GW |
| 20 Sept, 14:00 | 104.1 GW | 105.6 GW |
| 20 Sept, 15:00 | 106.1 GW | 107.9 GW |
| 20 Sept, 16:00 | 107.8 GW | 109.3 GW |
| 20 Sept, 17:00 | 108.8 GW | 108.7 GW |
| 20 Sept, 18:00 | 108.4 GW | 106.6 GW |
| 20 Sept, 19:00 | 108.1 GW | 104.6 GW |
| 20 Sept, 20:00 | 106.3 GW | 101.0 GW |
| 20 Sept, 21:00 | 102.1 GW | 95,733 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.