SEC Demand Forecast Accuracy: Error, Bias and Worst Miss, 21 August to 20 September 2026
The day-ahead demand forecast for SEC was off by 11.8% on average (mean absolute percentage error) over 717 hours from 21 August to 20 September 2026, and 38% of hours landed within 5% of the reading. Its bias was +4.9%: it ran high on average, an over forecast. The largest miss was 345 MW (52.9%) too low at 10 Sept 2026, 11:00 EDT (UTC-04:00). Dates and times are local (America/New_York).
Key Facts
- The day-ahead demand forecast for SEC was off by 11.8% on average (mean absolute percentage error) over 717 hours from 21 August to 20 September 2026, and 38% of hours landed within 5% of the reading. Its bias was +4.9%: it ran high on average, an over forecast. The largest miss was 345 MW (52.9%) too low at 10 Sept 2026, 11:00 EDT (UTC-04:00).
- Across 53 US grids ranked by average error over their own latest 30 day windows, SEC came 47 (1 is the smallest error).
- On average the forecast differed from reported demand by 30 MW, against average demand of 258 MW.
- The forecast was above reported demand in 47% of compared hours.
Forecast Error at a Glance
717 hours from 21 August to 20 September 2026Average error11.8%
Bias+4.9%
Hours within 5%38%
Worst miss345 MW
Average error is the mean absolute percentage gap between the forecast and reported demand. Bias is the signed mean (+9 MW per hour on average): the forecast ran high on average, an over forecast. The worst miss was 345 MW (52.9%) too low at 10 Sept 2026, 11:00 EDT (UTC-04:00): forecast 307 MW, reported 652 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, 21:00 EDT (UTC-04:00)Data to 2026-09-20
| Local hour | Reported demand | Day-ahead forecast |
|---|---|---|
| 13 Sept, 22:00 | 238 MW | 263 MW |
| 13 Sept, 23:00 | 253 MW | 233 MW |
| 14 Sept, 00:00 | 230 MW | 225 MW |
| 14 Sept, 01:00 | 208 MW | 208 MW |
| 14 Sept, 02:00 | 197 MW | 195 MW |
| 14 Sept, 03:00 | 193 MW | 189 MW |
| 14 Sept, 04:00 | 194 MW | 188 MW |
| 14 Sept, 05:00 | 209 MW | 197 MW |
| 14 Sept, 06:00 | 223 MW | 208 MW |
| 14 Sept, 07:00 | 227 MW | 209 MW |
| 14 Sept, 08:00 | 232 MW | 222 MW |
| 14 Sept, 09:00 | 235 MW | 250 MW |
| 14 Sept, 10:00 | 250 MW | 282 MW |
| 14 Sept, 11:00 | 273 MW | 321 MW |
| 14 Sept, 12:00 | 307 MW | 354 MW |
| 14 Sept, 13:00 | 336 MW | 376 MW |
| 14 Sept, 14:00 | 354 MW | 389 MW |
| 14 Sept, 15:00 | 364 MW | 391 MW |
| 14 Sept, 16:00 | 370 MW | 397 MW |
| 14 Sept, 17:00 | 349 MW | 391 MW |
| 14 Sept, 18:00 | 329 MW | 377 MW |
| 14 Sept, 19:00 | 312 MW | 353 MW |
| 14 Sept, 20:00 | 287 MW | 335 MW |
| 14 Sept, 21:00 | 252 MW | 310 MW |
| 14 Sept, 22:00 | 220 MW | 275 MW |
| 14 Sept, 23:00 | 230 MW | 247 MW |
| 15 Sept, 00:00 | 232 MW | 224 MW |
| 15 Sept, 01:00 | 211 MW | 207 MW |
| 15 Sept, 02:00 | 197 MW | 196 MW |
| 15 Sept, 03:00 | 193 MW | 189 MW |
| 15 Sept, 04:00 | 191 MW | 190 MW |
| 15 Sept, 05:00 | 199 MW | 197 MW |
| 15 Sept, 06:00 | 217 MW | 210 MW |
| 15 Sept, 07:00 | 215 MW | 212 MW |
| 15 Sept, 08:00 | 216 MW | 223 MW |
| 15 Sept, 09:00 | 188 MW | 245 MW |
| 15 Sept, 10:00 | 210 MW | 277 MW |
| 15 Sept, 11:00 | 230 MW | 311 MW |
| 15 Sept, 12:00 | 248 MW | 339 MW |
| 15 Sept, 13:00 | 271 MW | 355 MW |
| 15 Sept, 14:00 | 297 MW | 361 MW |
| 15 Sept, 15:00 | 299 MW | 362 MW |
| 15 Sept, 16:00 | 300 MW | 367 MW |
| 15 Sept, 17:00 | 305 MW | 365 MW |
| 15 Sept, 18:00 | 291 MW | 353 MW |
| 15 Sept, 19:00 | 288 MW | 338 MW |
| 15 Sept, 20:00 | 269 MW | 323 MW |
| 15 Sept, 21:00 | 238 MW | 298 MW |
| 15 Sept, 22:00 | 224 MW | 268 MW |
| 15 Sept, 23:00 | 236 MW | 241 MW |
| 16 Sept, 00:00 | 224 MW | 215 MW |
| 16 Sept, 01:00 | 209 MW | 199 MW |
| 16 Sept, 02:00 | 201 MW | 190 MW |
| 16 Sept, 03:00 | 188 MW | 183 MW |
| 16 Sept, 04:00 | 189 MW | 185 MW |
| 16 Sept, 05:00 | 186 MW | 195 MW |
| 16 Sept, 06:00 | 207 MW | 205 MW |
| 16 Sept, 07:00 | 205 MW | 208 MW |
| 16 Sept, 08:00 | 217 MW | 218 MW |
| 16 Sept, 09:00 | 241 MW | 236 MW |
| 16 Sept, 10:00 | 258 MW | 262 MW |
| 16 Sept, 11:00 | 251 MW | 291 MW |
| 16 Sept, 12:00 | 265 MW | 316 MW |
| 16 Sept, 13:00 | 259 MW | 334 MW |
| 16 Sept, 14:00 | 294 MW | 345 MW |
| 16 Sept, 15:00 | 321 MW | 353 MW |
| 16 Sept, 16:00 | 331 MW | 359 MW |
| 16 Sept, 17:00 | 319 MW | 358 MW |
| 16 Sept, 18:00 | 303 MW | 343 MW |
| 16 Sept, 19:00 | 272 MW | 327 MW |
| 16 Sept, 20:00 | 255 MW | 312 MW |
| 16 Sept, 21:00 | 244 MW | 288 MW |
| 16 Sept, 22:00 | 247 MW | 259 MW |
| 16 Sept, 23:00 | 228 MW | 229 MW |
| 17 Sept, 00:00 | 207 MW | 208 MW |
| 17 Sept, 01:00 | 193 MW | 190 MW |
| 17 Sept, 02:00 | 182 MW | 179 MW |
| 17 Sept, 03:00 | 177 MW | 171 MW |
| 17 Sept, 04:00 | 179 MW | 171 MW |
| 17 Sept, 05:00 | 185 MW | 178 MW |
| 17 Sept, 06:00 | 200 MW | 190 MW |
| 17 Sept, 07:00 | 196 MW | 195 MW |
| 17 Sept, 08:00 | 208 MW | 204 MW |
| 17 Sept, 09:00 | 228 MW | 221 MW |
| 17 Sept, 10:00 | 251 MW | 244 MW |
| 17 Sept, 11:00 | 270 MW | 275 MW |
| 17 Sept, 12:00 | 267 MW | 301 MW |
| 17 Sept, 13:00 | 273 MW | 326 MW |
| 17 Sept, 14:00 | 283 MW | 342 MW |
| 17 Sept, 15:00 | 305 MW | 348 MW |
| 17 Sept, 16:00 | 318 MW | 358 MW |
| 17 Sept, 17:00 | 318 MW | 356 MW |
| 17 Sept, 18:00 | 308 MW | 341 MW |
| 17 Sept, 19:00 | 282 MW | 324 MW |
| 17 Sept, 20:00 | 260 MW | 307 MW |
| 17 Sept, 21:00 | 233 MW | 282 MW |
| 17 Sept, 22:00 | 260 MW | 252 MW |
| 17 Sept, 23:00 | 229 MW | 221 MW |
| 18 Sept, 00:00 | 206 MW | 198 MW |
| 18 Sept, 01:00 | 184 MW | 181 MW |
| 18 Sept, 02:00 | 174 MW | 172 MW |
| 18 Sept, 03:00 | 168 MW | 165 MW |
| 18 Sept, 04:00 | 170 MW | 166 MW |
| 18 Sept, 05:00 | 181 MW | 174 MW |
| 18 Sept, 06:00 | 192 MW | 186 MW |
| 18 Sept, 07:00 | 193 MW | 191 MW |
| 18 Sept, 08:00 | 206 MW | 200 MW |
| 18 Sept, 09:00 | 227 MW | 221 MW |
| 18 Sept, 10:00 | 255 MW | 247 MW |
| 18 Sept, 11:00 | 261 MW | 279 MW |
| 18 Sept, 12:00 | 258 MW | 309 MW |
| 18 Sept, 13:00 | 268 MW | 334 MW |
| 18 Sept, 14:00 | 267 MW | 350 MW |
| 18 Sept, 15:00 | 289 MW | 359 MW |
| 18 Sept, 16:00 | 299 MW | 368 MW |
| 18 Sept, 17:00 | 304 MW | 363 MW |
| 18 Sept, 18:00 | 286 MW | 348 MW |
| 18 Sept, 19:00 | 269 MW | 326 MW |
| 18 Sept, 20:00 | 235 MW | 307 MW |
| 18 Sept, 21:00 | 227 MW | 283 MW |
| 18 Sept, 22:00 | 197 MW | 255 MW |
| 18 Sept, 23:00 | 211 MW | 229 MW |
| 19 Sept, 00:00 | 199 MW | 194 MW |
| 19 Sept, 01:00 | 182 MW | 177 MW |
| 19 Sept, 02:00 | 172 MW | 166 MW |
| 19 Sept, 03:00 | 160 MW | 157 MW |
| 19 Sept, 04:00 | 159 MW | 154 MW |
| 19 Sept, 05:00 | 155 MW | 156 MW |
| 19 Sept, 06:00 | 161 MW | 159 MW |
| 19 Sept, 07:00 | 170 MW | 169 MW |
| 19 Sept, 08:00 | 205 MW | 191 MW |
| 19 Sept, 09:00 | 263 MW | 216 MW |
| 19 Sept, 10:00 | 278 MW | 246 MW |
| 19 Sept, 11:00 | 273 MW | 277 MW |
| 19 Sept, 12:00 | 288 MW | 307 MW |
| 19 Sept, 13:00 | 291 MW | 332 MW |
| 19 Sept, 14:00 | 316 MW | 345 MW |
| 19 Sept, 15:00 | 339 MW | 357 MW |
| 19 Sept, 16:00 | 354 MW | 364 MW |
| 19 Sept, 17:00 | 339 MW | 361 MW |
| 19 Sept, 18:00 | 310 MW | 344 MW |
| 19 Sept, 19:00 | 279 MW | 323 MW |
| 19 Sept, 20:00 | 256 MW | 303 MW |
| 19 Sept, 21:00 | 240 MW | 278 MW |
| 19 Sept, 22:00 | 249 MW | 251 MW |
| 19 Sept, 23:00 | 251 MW | 226 MW |
| 20 Sept, 00:00 | 266 MW | 207 MW |
| 20 Sept, 01:00 | 244 MW | 189 MW |
| 20 Sept, 02:00 | 228 MW | 176 MW |
| 20 Sept, 03:00 | 218 MW | 167 MW |
| 20 Sept, 04:00 | 210 MW | 162 MW |
| 20 Sept, 05:00 | 210 MW | 161 MW |
| 20 Sept, 06:00 | 214 MW | 164 MW |
| 20 Sept, 07:00 | 222 MW | 173 MW |
| 20 Sept, 08:00 | 247 MW | 198 MW |
| 20 Sept, 09:00 | 280 MW | 223 MW |
| 20 Sept, 10:00 | 306 MW | 248 MW |
| 20 Sept, 11:00 | 329 MW | 277 MW |
| 20 Sept, 12:00 | 367 MW | 305 MW |
| 20 Sept, 13:00 | 379 MW | 322 MW |
| 20 Sept, 14:00 | 371 MW | 335 MW |
| 20 Sept, 15:00 | 360 MW | 338 MW |
| 20 Sept, 16:00 | 359 MW | 337 MW |
| 20 Sept, 17:00 | 364 MW | 331 MW |
| 20 Sept, 18:00 | 359 MW | 316 MW |
| 20 Sept, 19:00 | 357 MW | 299 MW |
| 20 Sept, 20:00 | 347 MW | 284 MW |
| 20 Sept, 21:00 | 320 MW | 260 MW |
Assumptions
- Only hours with both a forecast and a positive demand reading count (717 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.