Which weather model is most accurate in Chicago?
Chicago, Illinois · daily high temperature in °F · 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 (2026-07-12 to 2026-08-11), for daily high temperature.
One day out, NOAA AIGFS (AI) has been most accurate (typical miss 1.87°F); at three days, ECMWF AIFS (AI) (2.42°F); at seven days, ECMWF AIFS (AI) (3.64°F).
The largest standing bias belongs to DWD ICON, which has run warm by about 3.49°F at 3-day lead over this window.
The Spread's own bias-corrected blend scored a 1.76°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) in °F 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 |
|---|---|---|---|---|
| NOAA AIGFS (AI) | 1.9° (-0.2°) | 2.9° (-0.1°) | 3.7° (+1.2°) | 31 |
| ECMWF AIFS (AI) | 2.1° (-0.9°) | 2.4° (-0.7°) | 3.6° (+0.7°) | 31 |
| ECMWF IFS | 2.6° (+0.9°) | 3.5° (+2.2°) | 7.1° (+6.3°) | 31 |
| DWD ICON | 3.1° (+2.8°) | 4.3° (+3.5°) | — | 31 |
| NOAA GFS | 3.7° (+0.3°) | 3.3° (+1.6°) | 6.2° (+3.8°) | 31 |
| GEM (Canada) | 3.9° (+2.9°) | 2.8° (-0.7°) | 4.8° (+1.7°) | 31 |
| UKMO (UK) | 3.9° (+3.0°) | 4.7° (+3.2°) | — | 31 |
| NBM (US blend) | 2.5° (+0.0°) | 3.0° (+0.1°) | 3.5° (+1.4°) | 31 |
| Blended (bias-corrected) | 1.8° (-0.0°) | 2.4° (+0.0°) | 3.3° (+0.0°) | 31 |
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.
- Sun Aug 9 13 days out the models said 68–92; it hit 78. AIFS led (off 0.3°F); UKMO ran 14°F hot.
- Sat Aug 8 12 days out the models said 73–93; it hit 80. ECMWF led (off 0.3°F); GFS ran 4°F cold.
- Fri Aug 7 11 days out the models said 76–88; it hit 83. AIGFS led (off 0.0°F); ICON ran 4°F hot.
- Thu Aug 6 10 days out the models said 72–85; it hit 78. ECMWF led (off 0.5°F); GFS ran 5°F cold.
- Wed Aug 5 9 days out the models said 78–84; it hit 84. UKMO led (off 1.3°F); AIFS ran 6°F cold.
- Tue Aug 4 8 days out the models said 81–89; it hit 84. ECMWF led (off 0.1°F); GFS ran 5°F cold.
- Mon Aug 3 7 days out the models said 80–84; it hit 78. GEM led (off 0.1°F); GFS ran 6°F cold.
- Sun Aug 2 6 days out the models said 75–80; it hit 72. UKMO led (off 0.1°F); ICON ran 5°F hot.
- Sat Aug 1 5 days out the models said 73–78; it hit 72. AIFS led (off 0.3°F).
- Fri Jul 31 4 days out the models said 76–89; it hit 81. AIGFS led (off 0.2°F); AIFS ran 4°F cold.
- Thu Jul 30 3 days out the models said 81–90; it hit 84. AIGFS led (off 0.2°F); GFS ran 8°F cold.
Other cities
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The Spread — the forecast spread — is in closed beta. These verification pages are public while the rest is gated.