TPWR Demand Forecast Accuracy: Error, Bias and Worst Miss, 21 August to 20 September 2026
The day-ahead demand forecast for TPWR was off by 2.0% on average (mean absolute percentage error) over 719 hours from 21 August to 20 September 2026, and 95% of hours landed within 5% of the reading. Its bias was +1.3%: it ran high on average, an over forecast. The largest miss was 38 MW (7.4%) too high at 31 Aug 2026, 19:00 PDT (UTC-07:00). Dates and times are local (America/Los_Angeles).
Key Facts
- The day-ahead demand forecast for TPWR was off by 2.0% on average (mean absolute percentage error) over 719 hours from 21 August to 20 September 2026, and 95% of hours landed within 5% of the reading. Its bias was +1.3%: it ran high on average, an over forecast. The largest miss was 38 MW (7.4%) too high at 31 Aug 2026, 19:00 PDT (UTC-07:00).
- Across 53 US grids ranked by average error over their own latest 30 day windows, TPWR came 6 (1 is the smallest error).
- On average the forecast differed from reported demand by 9 MW, against average demand of 432 MW.
- The forecast was above reported demand in 73% of compared hours.
Forecast Error at a Glance
719 hours from 21 August to 20 September 2026Average error2.0%
Bias+1.3%
Hours within 5%95%
Worst miss38 MW
Average error is the mean absolute percentage gap between the forecast and reported demand. Bias is the signed mean (+5 MW per hour on average): the forecast ran high on average, an over forecast. The worst miss was 38 MW (7.4%) too high at 31 Aug 2026, 19:00 PDT (UTC-07:00): forecast 550 MW, reported 512 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)Data to 2026-09-20
| Local hour | Reported demand | Day-ahead forecast |
|---|---|---|
| 13 Sept, 19:00 | 477 MW | 472 MW |
| 13 Sept, 20:00 | 481 MW | 467 MW |
| 13 Sept, 21:00 | 453 MW | 447 MW |
| 13 Sept, 22:00 | 416 MW | 416 MW |
| 13 Sept, 23:00 | 391 MW | 381 MW |
| 14 Sept, 00:00 | 361 MW | 353 MW |
| 14 Sept, 01:00 | 347 MW | 339 MW |
| 14 Sept, 02:00 | 342 MW | 332 MW |
| 14 Sept, 03:00 | 343 MW | 333 MW |
| 14 Sept, 04:00 | 357 MW | 345 MW |
| 14 Sept, 05:00 | 386 MW | 377 MW |
| 14 Sept, 06:00 | 431 MW | 425 MW |
| 14 Sept, 07:00 | 460 MW | 449 MW |
| 14 Sept, 08:00 | 468 MW | 463 MW |
| 14 Sept, 09:00 | 469 MW | 471 MW |
| 14 Sept, 10:00 | 475 MW | 474 MW |
| 14 Sept, 11:00 | 478 MW | 480 MW |
| 14 Sept, 12:00 | 482 MW | 484 MW |
| 14 Sept, 13:00 | 478 MW | 482 MW |
| 14 Sept, 14:00 | 476 MW | 481 MW |
| 14 Sept, 15:00 | 469 MW | 482 MW |
| 14 Sept, 16:00 | 481 MW | 489 MW |
| 14 Sept, 17:00 | 478 MW | 498 MW |
| 14 Sept, 18:00 | 487 MW | 499 MW |
| 14 Sept, 19:00 | 494 MW | 501 MW |
| 14 Sept, 20:00 | 488 MW | 497 MW |
| 14 Sept, 21:00 | 458 MW | 467 MW |
| 14 Sept, 22:00 | 415 MW | 432 MW |
| 14 Sept, 23:00 | 388 MW | 395 MW |
| 15 Sept, 00:00 | 366 MW | 363 MW |
| 15 Sept, 01:00 | 345 MW | 347 MW |
| 15 Sept, 02:00 | 341 MW | 340 MW |
| 15 Sept, 03:00 | 339 MW | 341 MW |
| 15 Sept, 04:00 | 356 MW | 352 MW |
| 15 Sept, 05:00 | 386 MW | 382 MW |
| 15 Sept, 06:00 | 428 MW | 431 MW |
| 15 Sept, 07:00 | 457 MW | 456 MW |
| 15 Sept, 08:00 | 472 MW | 467 MW |
| 15 Sept, 09:00 | 477 MW | 474 MW |
| 15 Sept, 10:00 | 477 MW | 476 MW |
| 15 Sept, 11:00 | 484 MW | 480 MW |
| 15 Sept, 12:00 | 480 MW | 480 MW |
| 15 Sept, 13:00 | 477 MW | 479 MW |
| 15 Sept, 14:00 | 471 MW | 475 MW |
| 15 Sept, 15:00 | 473 MW | 475 MW |
| 15 Sept, 16:00 | 476 MW | 479 MW |
| 15 Sept, 17:00 | 485 MW | 488 MW |
| 15 Sept, 18:00 | 493 MW | 490 MW |
| 15 Sept, 19:00 | 502 MW | 495 MW |
| 15 Sept, 20:00 | 493 MW | 489 MW |
| 15 Sept, 21:00 | 470 MW | 464 MW |
| 15 Sept, 22:00 | 428 MW | 428 MW |
| 15 Sept, 23:00 | 394 MW | 395 MW |
| 16 Sept, 00:00 | 373 MW | 367 MW |
| 16 Sept, 01:00 | 356 MW | 351 MW |
| 16 Sept, 02:00 | 349 MW | 342 MW |
| 16 Sept, 03:00 | 349 MW | 342 MW |
| 16 Sept, 04:00 | 366 MW | 353 MW |
| 16 Sept, 05:00 | 388 MW | 386 MW |
| 16 Sept, 06:00 | 439 MW | 428 MW |
| 16 Sept, 07:00 | 467 MW | 453 MW |
| 16 Sept, 08:00 | 474 MW | 464 MW |
| 16 Sept, 09:00 | 470 MW | 468 MW |
| 16 Sept, 10:00 | 471 MW | 470 MW |
| 16 Sept, 11:00 | 478 MW | 477 MW |
| 16 Sept, 12:00 | 479 MW | 482 MW |
| 16 Sept, 13:00 | 472 MW | 490 MW |
| 16 Sept, 14:00 | 482 MW | 495 MW |
| 16 Sept, 15:00 | 482 MW | 503 MW |
| 16 Sept, 16:00 | 500 MW | 514 MW |
| 16 Sept, 17:00 | 503 MW | 521 MW |
| 16 Sept, 18:00 | 506 MW | 517 MW |
| 16 Sept, 19:00 | 507 MW | 515 MW |
| 16 Sept, 20:00 | 507 MW | 511 MW |
| 16 Sept, 21:00 | 469 MW | 481 MW |
| 16 Sept, 22:00 | 438 MW | 441 MW |
| 16 Sept, 23:00 | 393 MW | 401 MW |
| 17 Sept, 00:00 | 373 MW | 368 MW |
| 17 Sept, 01:00 | 353 MW | 350 MW |
| 17 Sept, 02:00 | 345 MW | 340 MW |
| 17 Sept, 03:00 | 342 MW | 340 MW |
| 17 Sept, 04:00 | 357 MW | 350 MW |
| 17 Sept, 05:00 | 382 MW | 379 MW |
| 17 Sept, 06:00 | 430 MW | 417 MW |
| 17 Sept, 07:00 | 460 MW | 441 MW |
| 17 Sept, 08:00 | 464 MW | 454 MW |
| 17 Sept, 09:00 | 466 MW | 465 MW |
| 17 Sept, 10:00 | 472 MW | 471 MW |
| 17 Sept, 11:00 | 478 MW | 480 MW |
| 17 Sept, 12:00 | 484 MW | 486 MW |
| 17 Sept, 13:00 | 489 MW | 498 MW |
| 17 Sept, 14:00 | 497 MW | 506 MW |
| 17 Sept, 15:00 | 502 MW | 515 MW |
| 17 Sept, 16:00 | 511 MW | 525 MW |
| 17 Sept, 17:00 | 524 MW | 530 MW |
| 17 Sept, 18:00 | 512 MW | 523 MW |
| 17 Sept, 19:00 | 519 MW | 521 MW |
| 17 Sept, 20:00 | 503 MW | 517 MW |
| 17 Sept, 21:00 | 469 MW | 485 MW |
| 17 Sept, 22:00 | 430 MW | 444 MW |
| 17 Sept, 23:00 | 395 MW | 404 MW |
| 18 Sept, 00:00 | 372 MW | 370 MW |
| 18 Sept, 01:00 | 354 MW | 352 MW |
| 18 Sept, 02:00 | 342 MW | 343 MW |
| 18 Sept, 03:00 | 338 MW | 343 MW |
| 18 Sept, 04:00 | 356 MW | 351 MW |
| 18 Sept, 05:00 | 375 MW | 378 MW |
| 18 Sept, 06:00 | 420 MW | 413 MW |
| 18 Sept, 07:00 | 442 MW | 438 MW |
| 18 Sept, 08:00 | 452 MW | 451 MW |
| 18 Sept, 09:00 | 465 MW | 462 MW |
| 18 Sept, 10:00 | 464 MW | 465 MW |
| 18 Sept, 11:00 | 475 MW | 470 MW |
| 18 Sept, 12:00 | 465 MW | 472 MW |
| 18 Sept, 13:00 | 467 MW | 477 MW |
| 18 Sept, 14:00 | 465 MW | 479 MW |
| 18 Sept, 15:00 | 472 MW | 483 MW |
| 18 Sept, 16:00 | 482 MW | 490 MW |
| 18 Sept, 17:00 | 480 MW | 493 MW |
| 18 Sept, 18:00 | 479 MW | 487 MW |
| 18 Sept, 19:00 | 481 MW | 483 MW |
| 18 Sept, 20:00 | 465 MW | 476 MW |
| 18 Sept, 21:00 | 447 MW | 454 MW |
| 18 Sept, 22:00 | 413 MW | 422 MW |
| 18 Sept, 23:00 | 383 MW | 392 MW |
| 19 Sept, 00:00 | 367 MW | 368 MW |
| 19 Sept, 01:00 | 345 MW | 351 MW |
| 19 Sept, 02:00 | 338 MW | 342 MW |
| 19 Sept, 03:00 | 331 MW | 339 MW |
| 19 Sept, 04:00 | 332 MW | 340 MW |
| 19 Sept, 05:00 | 343 MW | 347 MW |
| 19 Sept, 06:00 | 363 MW | 366 MW |
| 19 Sept, 07:00 | 389 MW | 383 MW |
| 19 Sept, 08:00 | 417 MW | 409 MW |
| 19 Sept, 09:00 | 432 MW | 429 MW |
| 19 Sept, 10:00 | 447 MW | 432 MW |
| 19 Sept, 11:00 | 443 MW | 433 MW |
| 19 Sept, 12:00 | 444 MW | 431 MW |
| 19 Sept, 13:00 | 431 MW | 429 MW |
| 19 Sept, 14:00 | 431 MW | 430 MW |
| 19 Sept, 15:00 | 427 MW | 431 MW |
| 19 Sept, 16:00 | 428 MW | 440 MW |
| 19 Sept, 17:00 | 443 MW | 446 MW |
| 19 Sept, 18:00 | 439 MW | 446 MW |
| 19 Sept, 19:00 | 447 MW | 451 MW |
| 19 Sept, 20:00 | 444 MW | 445 MW |
| 19 Sept, 21:00 | 419 MW | 427 MW |
| 19 Sept, 22:00 | 405 MW | 401 MW |
| 19 Sept, 23:00 | 382 MW | 375 MW |
| 20 Sept, 00:00 | 354 MW | 362 MW |
| 20 Sept, 01:00 | 341 MW | 347 MW |
| 20 Sept, 02:00 | 334 MW | 337 MW |
| 20 Sept, 03:00 | 331 MW | 334 MW |
| 20 Sept, 04:00 | 329 MW | 334 MW |
| 20 Sept, 05:00 | 343 MW | 344 MW |
| 20 Sept, 06:00 | 355 MW | 363 MW |
| 20 Sept, 07:00 | 379 MW | 382 MW |
| 20 Sept, 08:00 | 407 MW | 409 MW |
| 20 Sept, 09:00 | 428 MW | 426 MW |
| 20 Sept, 10:00 | 441 MW | 431 MW |
| 20 Sept, 11:00 | 446 MW | 433 MW |
| 20 Sept, 12:00 | 440 MW | 432 MW |
| 20 Sept, 13:00 | 443 MW | 431 MW |
| 20 Sept, 14:00 | 441 MW | 432 MW |
| 20 Sept, 15:00 | 450 MW | 437 MW |
| 20 Sept, 16:00 | 462 MW | 447 MW |
| 20 Sept, 17:00 | 480 MW | 458 MW |
| 20 Sept, 18:00 | 476 MW | 465 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.