SPA Demand Forecast Accuracy: Error, Bias and Worst Miss, 22 August to 20 September 2026

The day-ahead demand forecast for SPA was off by 33.5% on average (mean absolute percentage error) over 600 hours from 22 August to 20 September 2026, and 12% of hours landed within 5% of the reading. Its bias was +23.8%: it ran high on average, an over forecast. The largest miss was 28 MW (280.0%) too high at 14 Sept 2026, 18:00 CDT (UTC-05:00). Dates and times are local (America/Chicago).

Key Facts

The day-ahead demand forecast for SPA was off by 33.5% on average (mean absolute percentage error) over 600 hours from 22 August to 20 September 2026, and 12% of hours landed within 5% of the reading. Its bias was +23.8%: it ran high on average, an over forecast. The largest miss was 28 MW (280.0%) too high at 14 Sept 2026, 18:00 CDT (UTC-05:00).
Across 53 US grids ranked by average error over their own latest 30 day windows, SPA came 53 (1 is the smallest error).
On average the forecast differed from reported demand by 7 MW, against average demand of 24 MW.
The forecast was above reported demand in 70% of compared hours.

Forecast Error at a Glance

600 hours from 22 August to 20 September 2026

Average error33.5%

Bias+23.8%

Hours within 5%12%

Worst miss28 MW

Average error is the mean absolute percentage gap between the forecast and reported demand. Bias is the signed mean (+4 MW per hour on average): the forecast ran high on average, an over forecast. The worst miss was 28 MW (280.0%) too high at 14 Sept 2026, 18:00 CDT (UTC-05:00): forecast 38 MW, reported 10 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)

Hourly reported demand and the day-ahead forecast for SPA 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

SPA day-ahead demand forecast and reported demand by hour
Local hour	Reported demand	Day-ahead forecast
13 Sept, 21:00	25 MW	20 MW
13 Sept, 22:00	26 MW	23 MW
13 Sept, 23:00	18 MW	n/a
14 Sept, 00:00	18 MW	n/a
14 Sept, 01:00	29 MW	17 MW
14 Sept, 02:00	21 MW	17 MW
14 Sept, 03:00	30 MW	20 MW
14 Sept, 04:00	23 MW	20 MW
14 Sept, 05:00	24 MW	22 MW
14 Sept, 06:00	28 MW	24 MW
14 Sept, 07:00	22 MW	21 MW
14 Sept, 08:00	21 MW	27 MW
14 Sept, 09:00	21 MW	28 MW
14 Sept, 10:00	19 MW	28 MW
14 Sept, 11:00	25 MW	29 MW
14 Sept, 12:00	24 MW	35 MW
14 Sept, 13:00	27 MW	34 MW
14 Sept, 14:00	26 MW	36 MW
14 Sept, 15:00	21 MW	39 MW
14 Sept, 16:00	26 MW	38 MW
14 Sept, 17:00	27 MW	40 MW
14 Sept, 18:00	10 MW	38 MW
14 Sept, 19:00	26 MW	35 MW
14 Sept, 20:00	31 MW	34 MW
14 Sept, 21:00	18 MW	33 MW
14 Sept, 22:00	22 MW	26 MW
14 Sept, 23:00	23 MW	n/a
15 Sept, 00:00	21 MW	n/a
15 Sept, 01:00	18 MW	17 MW
15 Sept, 02:00	20 MW	16 MW
15 Sept, 03:00	27 MW	22 MW
15 Sept, 04:00	27 MW	22 MW
15 Sept, 05:00	16 MW	23 MW
15 Sept, 06:00	28 MW	26 MW
15 Sept, 07:00	20 MW	24 MW
15 Sept, 08:00	19 MW	28 MW
15 Sept, 09:00	23 MW	30 MW
15 Sept, 10:00	29 MW	34 MW
15 Sept, 11:00	29 MW	37 MW
15 Sept, 12:00	30 MW	37 MW
15 Sept, 13:00	31 MW	39 MW
15 Sept, 14:00	30 MW	40 MW
15 Sept, 15:00	31 MW	38 MW
15 Sept, 16:00	27 MW	41 MW
15 Sept, 17:00	26 MW	39 MW
15 Sept, 18:00	32 MW	39 MW
15 Sept, 19:00	15 MW	38 MW
15 Sept, 20:00	24 MW	32 MW
15 Sept, 21:00	23 MW	32 MW
15 Sept, 22:00	20 MW	29 MW
15 Sept, 23:00	18 MW	n/a
16 Sept, 00:00	20 MW	n/a
16 Sept, 01:00	12 MW	14 MW
16 Sept, 02:00	14 MW	17 MW
16 Sept, 03:00	18 MW	21 MW
16 Sept, 04:00	8 MW	22 MW
16 Sept, 05:00	25 MW	24 MW
16 Sept, 06:00	16 MW	23 MW
16 Sept, 07:00	20 MW	24 MW
16 Sept, 08:00	15 MW	27 MW
16 Sept, 09:00	29 MW	31 MW
16 Sept, 10:00	19 MW	31 MW
16 Sept, 11:00	26 MW	38 MW
16 Sept, 12:00	23 MW	37 MW
16 Sept, 13:00	21 MW	37 MW
16 Sept, 14:00	24 MW	39 MW
16 Sept, 15:00	28 MW	40 MW
16 Sept, 16:00	23 MW	40 MW
16 Sept, 17:00	35 MW	40 MW
16 Sept, 18:00	33 MW	38 MW
16 Sept, 19:00	17 MW	35 MW
16 Sept, 20:00	22 MW	35 MW
16 Sept, 21:00	23 MW	32 MW
16 Sept, 22:00	22 MW	29 MW
16 Sept, 23:00	16 MW	n/a
17 Sept, 00:00	26 MW	n/a
17 Sept, 01:00	20 MW	n/a
17 Sept, 02:00	18 MW	17 MW
17 Sept, 03:00	21 MW	21 MW
17 Sept, 04:00	26 MW	19 MW
17 Sept, 05:00	13 MW	22 MW
17 Sept, 06:00	24 MW	22 MW
17 Sept, 07:00	25 MW	22 MW
17 Sept, 08:00	22 MW	25 MW
17 Sept, 09:00	21 MW	26 MW
17 Sept, 10:00	25 MW	33 MW
17 Sept, 11:00	19 MW	34 MW
17 Sept, 12:00	25 MW	37 MW
17 Sept, 13:00	23 MW	36 MW
17 Sept, 14:00	30 MW	40 MW
17 Sept, 15:00	23 MW	37 MW
17 Sept, 16:00	25 MW	40 MW
17 Sept, 17:00	24 MW	38 MW
17 Sept, 18:00	28 MW	36 MW
17 Sept, 19:00	24 MW	35 MW
17 Sept, 20:00	16 MW	33 MW
17 Sept, 21:00	22 MW	30 MW
17 Sept, 22:00	20 MW	31 MW
17 Sept, 23:00	17 MW	n/a
18 Sept, 00:00	27 MW	n/a
18 Sept, 01:00	15 MW	n/a
18 Sept, 02:00	26 MW	15 MW
18 Sept, 03:00	18 MW	19 MW
18 Sept, 04:00	15 MW	20 MW
18 Sept, 05:00	30 MW	23 MW
18 Sept, 06:00	16 MW	23 MW
18 Sept, 07:00	17 MW	23 MW
18 Sept, 08:00	19 MW	25 MW
18 Sept, 09:00	21 MW	28 MW
18 Sept, 10:00	20 MW	29 MW
18 Sept, 11:00	19 MW	34 MW
18 Sept, 12:00	32 MW	35 MW
18 Sept, 13:00	27 MW	36 MW
18 Sept, 14:00	17 MW	37 MW
18 Sept, 15:00	27 MW	38 MW
18 Sept, 16:00	26 MW	37 MW
18 Sept, 17:00	23 MW	36 MW
18 Sept, 18:00	26 MW	37 MW
18 Sept, 19:00	21 MW	36 MW
18 Sept, 20:00	22 MW	31 MW
18 Sept, 21:00	24 MW	30 MW
18 Sept, 22:00	21 MW	26 MW
18 Sept, 23:00	26 MW	n/a
19 Sept, 00:00	37 MW	n/a
19 Sept, 01:00	11 MW	11 MW
19 Sept, 02:00	29 MW	14 MW
19 Sept, 03:00	24 MW	17 MW
19 Sept, 04:00	26 MW	18 MW
19 Sept, 05:00	25 MW	20 MW
19 Sept, 06:00	24 MW	18 MW
19 Sept, 07:00	21 MW	20 MW
19 Sept, 08:00	24 MW	20 MW
19 Sept, 09:00	25 MW	22 MW
19 Sept, 10:00	18 MW	28 MW
19 Sept, 11:00	27 MW	27 MW
19 Sept, 12:00	23 MW	29 MW
19 Sept, 13:00	13 MW	30 MW
19 Sept, 14:00	24 MW	31 MW
19 Sept, 15:00	18 MW	32 MW
19 Sept, 16:00	27 MW	31 MW
19 Sept, 17:00	25 MW	34 MW
19 Sept, 18:00	24 MW	32 MW
19 Sept, 19:00	18 MW	29 MW
19 Sept, 20:00	17 MW	29 MW
19 Sept, 21:00	41 MW	26 MW
19 Sept, 22:00	14 MW	23 MW
19 Sept, 23:00	22 MW	n/a
20 Sept, 00:00	25 MW	n/a
20 Sept, 01:00	15 MW	n/a
20 Sept, 02:00	22 MW	n/a
20 Sept, 03:00	12 MW	13 MW
20 Sept, 04:00	23 MW	18 MW
20 Sept, 05:00	12 MW	22 MW
20 Sept, 06:00	12 MW	16 MW
20 Sept, 07:00	18 MW	21 MW
20 Sept, 08:00	14 MW	21 MW
20 Sept, 09:00	20 MW	23 MW
20 Sept, 10:00	15 MW	25 MW
20 Sept, 11:00	18 MW	26 MW
20 Sept, 12:00	18 MW	28 MW
20 Sept, 13:00	14 MW	30 MW
20 Sept, 14:00	20 MW	30 MW
20 Sept, 15:00	18 MW	29 MW
20 Sept, 16:00	27 MW	30 MW
20 Sept, 17:00	25 MW	29 MW
20 Sept, 18:00	24 MW	26 MW
20 Sept, 19:00	18 MW	26 MW
20 Sept, 20:00	17 MW	23 MW

Assumptions

Only hours with both a forecast and a positive demand reading count (600 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.

SPA Demand Forecast Accuracy: Error, Bias and Worst Miss, 22 August to 20 September 2026

Key Facts

Forecast Error at a Glance

Forecast and Reported Demand, Last 7 Days

Assumptions

Related