The Spread

Which weather model is most accurate in San Francisco?

Outlook Model accuracy

San Francisco, California · 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 San Francisco at 1-, 3-, and 7-day leads, then scores those forecasts against the SFOC1 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, ECMWF IFS has been most accurate (typical miss 1.74°F); at three days, too close to call; at seven days, ECMWF AIFS (AI) (2.39°F).

The largest standing bias belongs to NOAA AIGFS (AI), which has run warm by about 6.09°F at 1-day lead over this window.

The Spread's own bias-corrected blend scored a 1.65°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
ECMWF IFS 1.7° (+0.2°) 2.1° (-0.1°) 2.9° (-1.8°) 30
GEM (Canada) 2.2° (-0.7°) 2.5° (-1.2°) 3.3° (-1.6°) 30
UKMO (UK) 2.6° (+1.8°) 2.7° (+1.2°) — 30
ECMWF AIFS (AI) 2.7° (+2.1°) 2.9° (+2.2°) 2.4° (+1.7°) 30
DWD ICON 3.2° (-3.2°) 3.3° (-2.9°) — 30
NOAA GFS 4.6° (+4.4°) 4.5° (+4.3°) 4.9° (+4.4°) 30
NOAA AIGFS (AI) 6.2° (+6.1°) 5.3° (+5.0°) 4.8° (+4.3°) 30
NBM (US blend) 2.4° (+0.7°) 2.7° (+0.6°) 2.8° (+1.0°) 30
Blended (bias-corrected) 1.6° (+0.0°) 1.9° (+0.0°) 2.2° (-0.0°) 30

Method, honestly

The Spread's San Francisco point is the San Francisco Downtown station (SFOC1), 0.4 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 SFOC1 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 10 days out the models said 68–74; it hit 69. GFS led (off 0.9°F); ECMWF ran 4°F cold.
  • Mon Aug 31 9 days out the models said 66–75; it hit 65. GFS led (off 0.0°F); GEM ran 3°F cold.
  • Sun Aug 30 8 days out the models said 60–75; it hit 65. UKMO led (off 0.1°F); ICON ran 3°F cold.
  • Sat Aug 29 7 days out the models said 62–77; it hit 66. GFS led (off 0.5°F); ICON ran 4°F cold.
  • Fri Aug 28 6 days out the models said 64–74; it hit 68. AIFS led (off 0.4°F); GFS ran 6°F hot.
  • Thu Aug 27 5 days out the models said 67–79; it hit 70. ECMWF led (off 0.4°F); AIGFS ran 8°F hot.
  • Wed Aug 26 4 days out the models said 64–75; it hit 69. ICON led (off 1.1°F); UKMO ran 11°F hot.
  • Tue Aug 25 3 days out the models said 64–72; it hit 70. GFS led (off 1.0°F); ICON ran 5°F cold.
  • Wed Aug 19 13 days out the models said 64–69; it hit 64. ICON led (off 1.5°F); AIGFS ran 11°F hot.
  • Tue Aug 18 13 days out the models said 64–76; it hit 64. GEM led (off 0.7°F); AIGFS ran 9°F hot.
  • Mon Aug 17 13 days out the models said 64–69; it hit 66. UKMO led (off 0.1°F); AIGFS ran 7°F hot.
  • Sun Aug 16 13 days out the models said 63–72; it hit 65. GEM led (off 1.2°F); AIGFS ran 7°F hot.
  • Sat Aug 15 13 days out the models said 63–70; it hit 64. ICON led (off 0.5°F); AIGFS ran 3°F hot.
  • Fri Aug 14 13 days out the models said 65–74; it hit 65. UKMO led (off 0.0°F).
  • Thu Aug 13 13 days out the models said 65–72; it hit 66. ECMWF led (off 0.3°F); AIGFS ran 3°F hot.
  • Wed Aug 12 13 days out the models said 62–75; it hit 66. GEM led (off 0.3°F); AIGFS ran 6°F hot.
  • Tue Aug 11 13 days out the models said 64–71; it hit 65. GFS led (off 0.6°F); AIGFS ran 7°F hot.
  • Mon Aug 10 13 days out the models said 66–73; it hit 66. GFS led (off 1.3°F); AIGFS ran 9°F hot.
  • Sun Aug 9 13 days out the models said 62–75; it hit 66. ICON led (off 2.5°F); AIGFS ran 16°F hot.
  • Sat Aug 8 12 days out the models said 64–75; it hit 62. ICON led (off 0.7°F); AIGFS ran 16°F hot.
  • Fri Aug 7 11 days out the models said 66–77; it hit 62. ICON led (off 2.0°F); AIGFS ran 14°F hot.
  • Thu Aug 6 10 days out the models said 69–81; it hit 65. ICON led (off 0.4°F); AIGFS ran 10°F hot.
  • Wed Aug 5 9 days out the models said 68–83; it hit 66. ICON led (off 0.1°F); AIGFS ran 12°F hot.
  • Tue Aug 4 8 days out the models said 66–85; it hit 67. ICON led (off 2.5°F); AIGFS ran 11°F hot.
  • Mon Aug 3 7 days out the models said 69–84; it hit 69. ICON led (off 2.2°F); AIGFS ran 14°F hot.
  • Sun Aug 2 6 days out the models said 65–81; it hit 72. GEM led (off 0.6°F); GFS ran 11°F hot.
  • Sat Aug 1 5 days out the models said 66–81; it hit 71. ECMWF led (off 1.3°F); AIGFS ran 10°F hot.
  • Fri Jul 31 4 days out the models said 64–80; it hit 69. ECMWF led (off 1.7°F); AIGFS ran 6°F hot.
  • Thu Jul 30 3 days out the models said 64–77; it hit 65. GEM led (off 0.3°F); AIGFS ran 9°F hot.

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The Spread — the forecast spread — is in closed beta. These verification pages are public while the rest is gated.