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 the MDW observations once the day has happened. This page covers the trailing 30 days (2026-08-04 to 2026-09-02), for daily high temperature.
One day out, too close to call; at three days, too close to call; at seven days, too close to call.
The largest standing bias belongs to ECMWF AIFS (AI), which has run cool by about 3.19°F at 3-day lead over this window.
The Spread's own bias-corrected blend scored a 0.94°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 |
|---|---|---|---|---|
| DWD ICON | 1.6° (-0.2°) | 2.9° (+0.7°) | — | 30 |
| NOAA GFS | 1.6° (+1.2°) | 3.2° (+2.6°) | 3.4° (+0.8°) | 30 |
| NOAA AIGFS (AI) | 2.0° (-1.9°) | 2.7° (-1.8°) | 4.0° (-2.8°) | 30 |
| UKMO (UK) | 2.0° (+0.6°) | 2.9° (+1.1°) | — | 30 |
| ECMWF IFS | 2.4° (-1.4°) | 2.6° (-0.7°) | 3.0° (-1.5°) | 30 |
| ECMWF AIFS (AI) | 3.0° (-3.0°) | 3.2° (-3.2°) | 4.2° (-4.0°) | 30 |
| GEM (Canada) | 3.1° (+2.7°) | 3.5° (-3.1°) | 3.0° (-1.9°) | 30 |
| NBM (US blend) | 2.6° (-2.2°) | 3.1° (-2.6°) | 4.7° (-4.5°) | 30 |
| Blended (bias-corrected) | 0.9° (+0.0°) | 1.7° (+0.0°) | 2.0° (+0.0°) | 30 |
Method, honestly
The Spread's Chicago point is the Chicago Midway station (MDW), 9 mi from downtown, used for both forecasts and verifications. 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 MDW observations — the station's own daily highs, a thermometer rather than a grid, and no correction applies: the thermometer is the truth outright. 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.
- Tue Sep 1 11 days out the models said 76–98; it hit 94. GFS led (off 0.1°F); AIFS ran 5°F cold.
- Mon Aug 31 10 days out the models said 80–96; it hit 91. GFS led (off 0.6°F); AIFS ran 6°F cold.
- Sun Aug 30 9 days out the models said 75–88; it hit 81. AIFS led (off 0.0°F); ICON ran 7°F hot.
- Sat Aug 29 8 days out the models said 76–86; it hit 82. ICON led (off 0.2°F); GEM ran 3°F hot.
- Fri Aug 28 7 days out the models said 74–83; it hit 84. GFS led (off 0.9°F); AIFS ran 4°F cold.
- Thu Aug 27 6 days out the models said 76–88; it hit 81. ECMWF led (off 0.3°F); GFS ran 4°F hot.
- Wed Aug 26 5 days out the models said 80–87; it hit 85. ICON led (off 0.4°F); AIFS ran 3°F cold.
- Tue Aug 25 4 days out the models said 76–84; it hit 81. UKMO led (off 0.4°F); AIFS ran 4°F cold.
- Mon Aug 24 3 days out the models said 74–82; it hit 79. GFS led (off 1.1°F); AIFS ran 4°F cold.
- Tue Aug 18 13 days out the models said 76–80; it hit 83. ICON led (off 0.8°F); AIFS ran 5°F cold.
- Mon Aug 17 13 days out the models said 74–80; it hit 78. UKMO led (off 0.6°F); GFS ran 4°F cold.
- Sun Aug 16 13 days out the models said 73–82; it hit 88. GEM led (off 1.2°F); GFS ran 5°F cold.
- Sat Aug 15 13 days out the models said 83–91; it hit 84. GEM led (off 2.9°F); AIGFS ran 8°F cold.
- Fri Aug 14 13 days out the models said 78–81; it hit 78. GEM led (off 0.3°F); UKMO ran 3°F hot.
- Thu Aug 13 13 days out the models said 71–83; it hit 79. ICON led (off 1.0°F); AIFS ran 4°F cold.
- Wed Aug 12 13 days out the models said 76–85; it hit 83. ECMWF led (off 1.0°F); UKMO ran 6°F cold.
- Tue Aug 11 13 days out the models said 73–91; it hit 79. ECMWF led (off 0.3°F); ICON ran 3°F hot.
- Mon Aug 10 13 days out the models said 70–99; it hit 84. UKMO led (off 1.4°F); GFS ran 6°F cold.
- 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.
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The Spread — the forecast spread — is in closed beta. These verification pages are public while the rest is gated.