GVL Demand Forecast Accuracy: Error, Bias and Worst Miss, 21 August to 20 September 2026
The day-ahead demand forecast for GVL was off by 10.7% on average (mean absolute percentage error) over 626 hours from 21 August to 20 September 2026, and 16% of hours landed within 5% of the reading. Its bias was -9.5%: it ran low on average, an under forecast. The largest miss was 95 MW (24.7%) too low at 3 Sept 2026, 18:00 EDT (UTC-04:00). Dates and times are local (America/New_York).
Key Facts
- The day-ahead demand forecast for GVL was off by 10.7% on average (mean absolute percentage error) over 626 hours from 21 August to 20 September 2026, and 16% of hours landed within 5% of the reading. Its bias was -9.5%: it ran low on average, an under forecast. The largest miss was 95 MW (24.7%) too low at 3 Sept 2026, 18:00 EDT (UTC-04:00).
- Across 53 US grids ranked by average error over their own latest 30 day windows, GVL came 45 (1 is the smallest error).
- On average the forecast differed from reported demand by 32 MW, against average demand of 298 MW.
- The forecast was above reported demand in 9% of compared hours.
Forecast Error at a Glance
626 hours from 21 August to 20 September 2026Average error10.7%
Bias-9.5%
Hours within 5%16%
Worst miss95 MW
Average error is the mean absolute percentage gap between the forecast and reported demand. Bias is the signed mean (-28 MW per hour on average): the forecast ran low on average, an under forecast. The worst miss was 95 MW (24.7%) too low at 3 Sept 2026, 18:00 EDT (UTC-04:00): forecast 290 MW, reported 385 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 | 316 MW | 274 MW |
| 13 Sept, 23:00 | 290 MW | 247 MW |
| 14 Sept, 00:00 | 267 MW | 241 MW |
| 14 Sept, 01:00 | 247 MW | 222 MW |
| 14 Sept, 02:00 | 233 MW | 205 MW |
| 14 Sept, 03:00 | 224 MW | 198 MW |
| 14 Sept, 04:00 | 223 MW | 194 MW |
| 14 Sept, 05:00 | 228 MW | 199 MW |
| 14 Sept, 06:00 | 242 MW | 211 MW |
| 14 Sept, 07:00 | 250 MW | 220 MW |
| 14 Sept, 08:00 | 264 MW | 232 MW |
| 14 Sept, 09:00 | 284 MW | 251 MW |
| 14 Sept, 10:00 | 311 MW | 271 MW |
| 14 Sept, 11:00 | 341 MW | 297 MW |
| 14 Sept, 12:00 | 362 MW | 322 MW |
| 14 Sept, 13:00 | 381 MW | 342 MW |
| 14 Sept, 14:00 | 398 MW | 358 MW |
| 14 Sept, 15:00 | 420 MW | 373 MW |
| 14 Sept, 16:00 | 434 MW | 384 MW |
| 14 Sept, 17:00 | 426 MW | 359 MW |
| 14 Sept, 18:00 | 404 MW | 329 MW |
| 14 Sept, 19:00 | 391 MW | 328 MW |
| 14 Sept, 20:00 | 376 MW | 315 MW |
| 14 Sept, 21:00 | 349 MW | 296 MW |
| 14 Sept, 22:00 | 320 MW | 270 MW |
| 14 Sept, 23:00 | 293 MW | 247 MW |
| 15 Sept, 00:00 | 268 MW | 238 MW |
| 15 Sept, 01:00 | 248 MW | 219 MW |
| 15 Sept, 02:00 | 233 MW | 206 MW |
| 15 Sept, 03:00 | 224 MW | 197 MW |
| 15 Sept, 04:00 | 220 MW | 195 MW |
| 15 Sept, 05:00 | 224 MW | 201 MW |
| 15 Sept, 06:00 | 240 MW | 214 MW |
| 15 Sept, 07:00 | 249 MW | 220 MW |
| 15 Sept, 08:00 | 263 MW | 228 MW |
| 15 Sept, 09:00 | 286 MW | 243 MW |
| 15 Sept, 10:00 | 309 MW | 266 MW |
| 15 Sept, 11:00 | 335 MW | 292 MW |
| 15 Sept, 12:00 | 363 MW | 317 MW |
| 15 Sept, 13:00 | 387 MW | 339 MW |
| 15 Sept, 14:00 | 403 MW | 353 MW |
| 15 Sept, 15:00 | 403 MW | 363 MW |
| 15 Sept, 16:00 | 383 MW | 370 MW |
| 15 Sept, 17:00 | 371 MW | 371 MW |
| 15 Sept, 18:00 | 359 MW | 363 MW |
| 15 Sept, 19:00 | 352 MW | 343 MW |
| 15 Sept, 20:00 | 347 MW | 332 MW |
| 15 Sept, 21:00 | 330 MW | 313 MW |
| 15 Sept, 22:00 | 307 MW | 288 MW |
| 15 Sept, 23:00 | 284 MW | 264 MW |
| 16 Sept, 00:00 | 263 MW | 241 MW |
| 16 Sept, 01:00 | 246 MW | 222 MW |
| 16 Sept, 02:00 | 234 MW | 205 MW |
| 16 Sept, 03:00 | 226 MW | 198 MW |
| 16 Sept, 04:00 | 222 MW | 194 MW |
| 16 Sept, 05:00 | 227 MW | 199 MW |
| 16 Sept, 06:00 | 241 MW | 211 MW |
| 16 Sept, 07:00 | 245 MW | 220 MW |
| 16 Sept, 08:00 | 255 MW | 232 MW |
| 16 Sept, 09:00 | 270 MW | 251 MW |
| 16 Sept, 10:00 | 290 MW | 271 MW |
| 16 Sept, 11:00 | 310 MW | 297 MW |
| 16 Sept, 12:00 | 330 MW | 322 MW |
| 16 Sept, 13:00 | 350 MW | 342 MW |
| 16 Sept, 14:00 | 365 MW | 358 MW |
| 16 Sept, 15:00 | 376 MW | 373 MW |
| 16 Sept, 16:00 | 387 MW | 384 MW |
| 16 Sept, 17:00 | 392 MW | 359 MW |
| 16 Sept, 18:00 | 384 MW | 329 MW |
| 16 Sept, 19:00 | 367 MW | 328 MW |
| 16 Sept, 20:00 | 350 MW | 315 MW |
| 16 Sept, 21:00 | 330 MW | 296 MW |
| 16 Sept, 22:00 | 303 MW | 270 MW |
| 16 Sept, 23:00 | 273 MW | 247 MW |
| 17 Sept, 00:00 | 249 MW | 235 MW |
| 17 Sept, 01:00 | 232 MW | 218 MW |
| 17 Sept, 02:00 | 218 MW | 205 MW |
| 17 Sept, 03:00 | 210 MW | 197 MW |
| 17 Sept, 04:00 | 208 MW | 194 MW |
| 17 Sept, 05:00 | 213 MW | 200 MW |
| 17 Sept, 06:00 | 226 MW | 216 MW |
| 17 Sept, 07:00 | 225 MW | 223 MW |
| 17 Sept, 08:00 | 225 MW | 235 MW |
| 17 Sept, 09:00 | 243 MW | 253 MW |
| 17 Sept, 10:00 | 261 MW | 278 MW |
| 17 Sept, 11:00 | 283 MW | 299 MW |
| 17 Sept, 12:00 | 302 MW | 324 MW |
| 17 Sept, 13:00 | 317 MW | 346 MW |
| 17 Sept, 14:00 | 327 MW | 364 MW |
| 17 Sept, 15:00 | 342 MW | 371 MW |
| 17 Sept, 16:00 | 368 MW | 378 MW |
| 17 Sept, 17:00 | 373 MW | 380 MW |
| 17 Sept, 18:00 | 366 MW | 373 MW |
| 17 Sept, 19:00 | 350 MW | 359 MW |
| 17 Sept, 20:00 | 337 MW | 349 MW |
| 17 Sept, 21:00 | 314 MW | 330 MW |
| 17 Sept, 22:00 | 287 MW | 302 MW |
| 17 Sept, 23:00 | 260 MW | 274 MW |
| 18 Sept, 00:00 | 238 MW | 240 MW |
| 18 Sept, 01:00 | 221 MW | 223 MW |
| 18 Sept, 02:00 | 208 MW | 211 MW |
| 18 Sept, 03:00 | 201 MW | 202 MW |
| 18 Sept, 04:00 | 199 MW | 197 MW |
| 18 Sept, 05:00 | 204 MW | 195 MW |
| 18 Sept, 06:00 | 218 MW | 199 MW |
| 18 Sept, 07:00 | 226 MW | 202 MW |
| 18 Sept, 08:00 | 235 MW | 215 MW |
| 18 Sept, 09:00 | 249 MW | 236 MW |
| 18 Sept, 10:00 | 269 MW | 259 MW |
| 18 Sept, 11:00 | 297 MW | 281 MW |
| 18 Sept, 12:00 | 325 MW | 302 MW |
| 18 Sept, 13:00 | 341 MW | 322 MW |
| 18 Sept, 14:00 | 355 MW | 338 MW |
| 18 Sept, 15:00 | 359 MW | 347 MW |
| 18 Sept, 16:00 | 355 MW | 352 MW |
| 18 Sept, 17:00 | 353 MW | 351 MW |
| 18 Sept, 18:00 | 353 MW | 340 MW |
| 18 Sept, 19:00 | 339 MW | 322 MW |
| 18 Sept, 20:00 | 325 MW | 308 MW |
| 18 Sept, 21:00 | 306 MW | 287 MW |
| 18 Sept, 22:00 | 285 MW | 264 MW |
| 18 Sept, 23:00 | 264 MW | 243 MW |
| 19 Sept, 00:00 | 242 MW | 210 MW |
| 19 Sept, 01:00 | 224 MW | 193 MW |
| 19 Sept, 02:00 | 210 MW | 181 MW |
| 19 Sept, 03:00 | 199 MW | 172 MW |
| 19 Sept, 04:00 | 194 MW | 167 MW |
| 19 Sept, 05:00 | 192 MW | 165 MW |
| 19 Sept, 06:00 | 195 MW | 169 MW |
| 19 Sept, 07:00 | 199 MW | 172 MW |
| 19 Sept, 08:00 | 216 MW | 185 MW |
| 19 Sept, 09:00 | 239 MW | 206 MW |
| 19 Sept, 10:00 | 262 MW | 229 MW |
| 19 Sept, 11:00 | 291 MW | 251 MW |
| 19 Sept, 12:00 | 323 MW | 272 MW |
| 19 Sept, 13:00 | 347 MW | 292 MW |
| 19 Sept, 14:00 | 356 MW | 308 MW |
| 19 Sept, 15:00 | 374 MW | 317 MW |
| 19 Sept, 16:00 | 381 MW | 322 MW |
| 19 Sept, 17:00 | 360 MW | 321 MW |
| 19 Sept, 18:00 | 338 MW | 310 MW |
| 19 Sept, 19:00 | 324 MW | 292 MW |
| 19 Sept, 20:00 | 313 MW | 278 MW |
| 19 Sept, 21:00 | 299 MW | 257 MW |
| 19 Sept, 22:00 | 282 MW | 234 MW |
| 19 Sept, 23:00 | 265 MW | 213 MW |
| 20 Sept, 00:00 | 246 MW | 220 MW |
| 20 Sept, 01:00 | 228 MW | 203 MW |
| 20 Sept, 02:00 | 215 MW | 189 MW |
| 20 Sept, 03:00 | 206 MW | 177 MW |
| 20 Sept, 04:00 | 200 MW | 171 MW |
| 20 Sept, 05:00 | 199 MW | 170 MW |
| 20 Sept, 06:00 | 201 MW | 174 MW |
| 20 Sept, 07:00 | 206 MW | 177 MW |
| 20 Sept, 08:00 | 220 MW | 193 MW |
| 20 Sept, 09:00 | 243 MW | 221 MW |
| 20 Sept, 10:00 | 269 MW | 255 MW |
| 20 Sept, 11:00 | 296 MW | 286 MW |
| 20 Sept, 12:00 | 317 MW | 311 MW |
| 20 Sept, 13:00 | 339 MW | 333 MW |
| 20 Sept, 14:00 | 356 MW | 347 MW |
| 20 Sept, 15:00 | 341 MW | 340 MW |
| 20 Sept, 16:00 | 314 MW | 341 MW |
| 20 Sept, 17:00 | 305 MW | 332 MW |
| 20 Sept, 18:00 | 300 MW | 311 MW |
| 20 Sept, 19:00 | 300 MW | 293 MW |
| 20 Sept, 20:00 | 298 MW | 290 MW |
| 20 Sept, 21:00 | 286 MW | 277 MW |
Assumptions
- Only hours with both a forecast and a positive demand reading count (626 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.