The Spread

Which weather model is most accurate in Seattle?

Outlook Model accuracy

Seattle, Washington · daily high temperature in °C · trailing 30 days · refreshed at most every 6 hours

Every day, The Spread archives what each major weather model predicted for Seattle at 1-, 3-, and 7-day leads, then scores those forecasts against the SEA 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 3.12°C at 1-day lead over this window.

The Spread's own bias-corrected blend scored a 0.92°C 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 °C 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
UKMO (UK) 1.1° (+0.4°) 1.5° (+0.4°) — 30
GEM (Canada) 1.2° (+0.8°) 2.0° (-1.4°) 2.3° (-1.4°) 30
ECMWF IFS 1.2° (-0.7°) 1.5° (-0.5°) 2.3° (-1.2°) 30
NOAA AIGFS (AI) 1.2° (-0.1°) 1.5° (+0.0°) 2.6° (-1.2°) 30
DWD ICON 1.8° (-1.7°) 1.9° (-1.2°) — 30
NOAA GFS 2.7° (+2.7°) 3.0° (+2.6°) 3.3° (+2.6°) 30
ECMWF AIFS (AI) 3.1° (-3.1°) 3.0° (-2.9°) 2.9° (-2.5°) 30
NBM (US blend) 1.4° (-0.7°) 1.7° (-0.8°) 2.4° (-1.6°) 30
Blended (bias-corrected) 0.9° (-0.0°) 1.3° (-0.0°) 1.7° (-0.0°) 30

Method, honestly

The Spread's Seattle point is the Seattle-Tacoma Intl station (SEA), 18 km 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 SEA 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 9 days out the models said 19–22; it hit 19. AIFS led (off 0.5°C); GFS ran 4°C hot.
  • Mon Aug 31 8 days out the models said 19–23; it hit 24. GEM led (off 0.1°C); AIFS ran 2°C cold.
  • Sun Aug 30 7 days out the models said 17–21; it hit 22. UKMO led (off 0.1°C); AIFS ran 2°C cold.
  • Sat Aug 29 6 days out the models said 18–23; it hit 22. GFS led (off 0.2°C); AIGFS ran 4°C cold.
  • Fri Aug 28 5 days out the models said 20–25; it hit 23. GEM led (off 0.1°C); AIGFS ran 2°C cold.
  • Thu Aug 27 4 days out the models said 20–25; it hit 23. GFS led (off 0.6°C); AIFS ran 2°C cold.
  • Wed Aug 26 3 days out the models said 23–28; it hit 25. GEM led (off 0.3°C); GFS ran 3°C hot.
  • Tue Aug 18 14 days out the models said 18–28; it hit 28. AIGFS led (off 0.0°C); AIFS ran 4°C cold.
  • Mon Aug 17 14 days out the models said 20–24; it hit 25. ECMWF led (off 0.2°C); AIFS ran 2°C cold.
  • Sun Aug 16 14 days out the models said 24–28; it hit 24. ECMWF led (off 0.1°C); AIFS ran 3°C cold.
  • Sat Aug 15 14 days out the models said 19–27; it hit 25. GEM led (off 0.6°C); AIFS ran 4°C cold.
  • Fri Aug 14 14 days out the models said 24–27; it hit 27. UKMO led (off 0.2°C); AIFS ran 3°C cold.
  • Thu Aug 13 14 days out the models said 19–25; it hit 26. ECMWF led (off 0.2°C); AIGFS ran 3°C hot.
  • Wed Aug 12 14 days out the models said 25–31; it hit 24. UKMO led (off 0.1°C); AIGFS ran 2°C hot.
  • Tue Aug 11 14 days out the models said 21–24; it hit 25. GEM led (off 0.1°C); AIGFS ran 2°C hot.
  • Mon Aug 10 14 days out the models said 25–26; it hit 24. GEM led (off 0.2°C); GFS ran 3°C cold.
  • Sun Aug 9 14 days out the models said 24–28; it hit 24. GEM led (off 0.1°C); AIFS ran 2°C cold.
  • Sat Aug 8 14 days out the models said 20–27; it hit 28. ECMWF led (off 0.1°C); AIFS ran 2°C cold.
  • Fri Aug 7 14 days out the models said 22–35; it hit 30. ECMWF led (off 0.3°C); AIFS ran 3°C cold.
  • Thu Aug 6 14 days out the models said 19–26; it hit 30. ECMWF led (off 0.2°C); AIGFS ran 3°C hot.
  • Wed Aug 5 14 days out the models said 22–27; it hit 29. ECMWF led (off 0.0°C); AIGFS ran 3°C hot.
  • Tue Aug 4 14 days out the models said 22–30; it hit 26. AIFS led (off 0.1°C); AIGFS ran 3°C hot.
  • Mon Aug 3 14 days out the models said 24–36; it hit 23. ECMWF led (off 0.3°C); AIGFS ran 2°C hot.
  • Sun Aug 2 14 days out the models said 19–29; it hit 21. ECMWF led (off 0.1°C); AIGFS ran 3°C cold.
  • Sat Aug 1 14 days out the models said 22–28; it hit 23. GEM led (off 0.4°C); AIFS ran 2°C cold.
  • Fri Jul 31 14 days out the models said 23–33; it hit 28. ECMWF led (off 0.1°C); AIGFS ran 3°C hot.
  • Thu Jul 30 13 days out the models said 21–31; it hit 25. UKMO led (off 0.2°C); AIGFS ran 2°C hot.
  • Wed Jul 29 12 days out the models said 22–30; it hit 23. GFS led (off 0.3°C); AIGFS ran 3°C hot.
  • Tue Jul 28 11 days out the models said 21–30; it hit 23. UKMO led (off 0.1°C); GFS ran 2°C cold.
  • Mon Jul 27 10 days out the models said 19–27; it hit 26. GEM led (off 0.0°C); AIFS ran 2°C cold.
  • Sun Jul 26 9 days out the models said 20–27; it hit 22. GEM led (off 0.0°C); ICON ran 3°C cold.
  • Sat Jul 25 8 days out the models said 22–25; it hit 22. ECMWF led (off 0.7°C); ICON ran 2°C cold.
  • Fri Jul 24 7 days out the models said 24–31; it hit 26. ICON led (off 0.3°C); AIFS ran 2°C cold.
  • Thu Jul 23 6 days out the models said 23–32; it hit 24. ECMWF led (off 0.1°C); AIFS ran 3°C cold.
  • Wed Jul 22 5 days out the models said 26–32; it hit 31. UKMO led (off 0.1°C); AIGFS ran 3°C hot.
  • Tue Jul 21 4 days out the models said 27–32; it hit 32. GEM led (off 0.4°C); ICON ran 3°C cold.
  • Mon Jul 20 3 days out the models said 24–31; it hit 26. GFS led (off 0.1°C); AIGFS ran 2°C hot.

Other cities

Atlanta, Georgia Berlin, State of Berlin Boston, Massachusetts Buffalo, New York Charlotte, North Carolina Chicago, Illinois Dallas, Texas Denver, Colorado Detroit, Michigan Houston, Texas London, England Los Angeles, California Miami, Florida Milan, Lombardy Minneapolis, Minnesota New Orleans, Louisiana New York, New York Oklahoma City, Oklahoma Orlando, Florida Paris, Île-de-France Region Philadelphia, Pennsylvania Phoenix, Arizona Salt Lake City, Utah San Antonio, Texas San Diego, California San Francisco, California St. Louis, Missouri Tampa, Florida Washington, District of Columbia

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