Which weather model is most accurate in Chicago?
Chicago, Illinois · daily high temperature · trailing 30 days · refreshed at most every 6 hours
Every day, The Spread archives what each major weather model predicted for Chicago at 1-, 3-, and 7-day leads, then scores those forecasts against ERA5 reanalysis once the day has happened. This page covers the trailing 30 days (2026-07-06 to 2026-08-05), for daily high temperature.
One day out, ECMWF AIFS (AI) has been most accurate (typical miss 1.67°F); at three days, ECMWF AIFS (AI) (2.18°F); at seven days, ECMWF AIFS (AI) (3.33°F).
The largest standing bias belongs to DWD ICON, which has run warm by about 3.87°F at 3-day lead over this window.
The Spread's own bias-corrected blend scored a 1.28°F typical miss at one day. Its corrections come from the same window it is scored on (in-sample), so read it as a ceiling, not a promise.
The scoreboard
Typical miss (MAE) with the signed bias in parentheses — positive bias means the model ran warm. Days = scored days behind the 1-day number.
| Model | 1-day | 3-day | 7-day | Days |
|---|---|---|---|---|
| ECMWF AIFS (AI) | 1.7° (-0.3°) | 2.2° (-0.1°) | 3.3° (+1.1°) | 30 |
| NOAA AIGFS (AI) | 1.9° (+0.1°) | 2.6° (+0.6°) | 4.0° (+2.0°) | 30 |
| ECMWF IFS | 2.5° (+1.5°) | 3.1° (+2.3°) | 7.1° (+6.1°) | 30 |
| DWD ICON | 3.1° (+2.7°) | 4.0° (+3.9°) | — | 30 |
| GEM (Canada) | 3.4° (+3.3°) | 2.4° (-0.2°) | 4.7° (+1.8°) | 30 |
| UKMO (UK) | 3.5° (+3.4°) | 4.3° (+3.5°) | — | 30 |
| NOAA GFS | 3.5° (-0.1°) | 3.0° (+0.8°) | 6.4° (+2.9°) | 30 |
| NBM (US blend) | 1.9° (+0.9°) | 2.5° (+1.0°) | 3.9° (+2.4°) | 30 |
| Blended (bias-corrected) | 1.3° (+0.0°) | 2.0° (-0.0°) | 3.0° (-0.0°) | 30 |
Method, honestly
Forecasts come from each model's actual archived runs via Open-Meteo's Previous Runs API — what the model said at the time, not a reconstruction. Truth is ERA5 reanalysis daily highs. Rankings cover the models themselves; the two consensus products at the bottom of the table — NBM, which is itself a blend of models, and The Spread's own bias-corrected blend — are shown for comparison, never ranked or named "most accurate" here. The blend's corrections come from the same trailing window it is scored on (in-sample), so treat its score as a ceiling. A rolling 30-day window means these numbers move — that is the point.
Receipts — was the forecast right?
One page per settled date: what every model said as the day approached, what happened, and who was closest.
- Mon Aug 3 7 days out the models said 80–84; it hit 78. GEM led (off 0.1°); GFS ran 6° cold.
- Sun Aug 2 6 days out the models said 75–80; it hit 72. UKMO led (off 0.1°); ICON ran 5° hot.
- Sat Aug 1 5 days out the models said 73–78; it hit 72. AIFS led (off 0.3°).
- Fri Jul 31 4 days out the models said 76–89; it hit 81. AIGFS led (off 0.2°); AIFS ran 4° cold.
- Thu Jul 30 3 days out the models said 81–90; it hit 84. AIGFS led (off 0.2°); GFS ran 8° cold.
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The Spread — the forecast spread — is in closed beta. These verification pages are public while the rest is gated.