The Spread

Which weather model is most accurate in Salt Lake City?

Outlook Model accuracy

Salt Lake City, Utah · 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 Salt Lake City at 1-, 3-, and 7-day leads, then scores those forecasts against the SLC 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 2.31°C at 1-day lead over this window.

The Spread's own bias-corrected blend scored a 0.56°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
DWD ICON 1.1° (-0.7°) 1.3° (-0.9°) — 30
NOAA GFS 1.1° (-0.2°) 1.2° (+0.3°) 2.9° (+1.1°) 30
GEM (Canada) 1.2° (-0.8°) 2.3° (-1.6°) 2.4° (-1.1°) 30
NOAA AIGFS (AI) 1.5° (-1.4°) 1.8° (-1.6°) 3.0° (-2.3°) 30
ECMWF IFS 1.6° (-1.4°) 1.4° (-0.8°) 2.5° (+1.0°) 30
UKMO (UK) 1.6° (-1.4°) 1.6° (-1.2°) — 30
ECMWF AIFS (AI) 2.3° (-2.3°) 2.2° (-2.2°) 2.9° (-2.5°) 30
NBM (US blend) 1.6° (-1.6°) 1.7° (-1.6°) 3.2° (-1.2°) 30
Blended (bias-corrected) 0.6° (+0.0°) 0.8° (-0.0°) 1.8° (-0.0°) 30

Method, honestly

The Spread's Salt Lake City point is the Salt Lake City Intl station (SLC), 7.1 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 SLC 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 12 days out the models said 29–37; it hit 29. GFS led (off 0.5°C); UKMO ran 3°C cold.
  • Mon Aug 31 11 days out the models said 28–36; it hit 31. GFS led (off 0.9°C); AIFS ran 6°C cold.
  • Sun Aug 30 10 days out the models said 26–33; it hit 28. GFS led (off 0.5°C); ECMWF ran 5°C cold.
  • Sat Aug 29 9 days out the models said 26–38; it hit 24. ECMWF led (off 0.0°C); GFS ran 5°C hot.
  • Fri Aug 28 8 days out the models said 26–37; it hit 33. UKMO led (off 0.1°C); AIFS ran 5°C cold.
  • Thu Aug 27 7 days out the models said 32–36; it hit 36. ICON led (off 0.2°C); AIFS ran 4°C cold.
  • Wed Aug 26 6 days out the models said 33–36; it hit 36. GFS led (off 0.2°C); AIFS ran 2°C cold.
  • Tue Aug 25 5 days out the models said 32–36; it hit 34. GEM led (off 0.2°C); AIFS ran 2°C cold.
  • Mon Aug 24 4 days out the models said 31–35; it hit 35. ICON led (off 0.0°C); AIFS ran 5°C cold.
  • Sun Aug 23 3 days out the models said 33–36; it hit 34. ICON led (off 0.1°C); AIFS ran 3°C cold.
  • Tue Aug 18 14 days out the models said 23–36; it hit 35. ICON led (off 0.0°C).
  • Mon Aug 17 14 days out the models said 24–36; it hit 35. GEM led (off 0.0°C); UKMO ran 2°C cold.
  • Sun Aug 16 14 days out the models said 23–38; it hit 33. GEM led (off 0.4°C); UKMO ran 2°C cold.
  • Sat Aug 15 14 days out the models said 28–33; it hit 28. UKMO led (off 0.2°C); GFS ran 2°C hot.
  • Fri Aug 14 14 days out the models said 29–38; it hit 25. UKMO led (off 0.3°C); GFS ran 3°C hot.
  • Thu Aug 13 14 days out the models said 28–38; it hit 24. GEM led (off 0.1°C); AIGFS ran 2°C hot.
  • Wed Aug 12 14 days out the models said 26–38; it hit 31. GFS led (off 0.2°C); AIFS ran 5°C cold.
  • Tue Aug 11 14 days out the models said 28–38; it hit 36. ECMWF led (off 0.2°C); AIFS ran 3°C cold.
  • Mon Aug 10 14 days out the models said 32–37; it hit 36. AIGFS led (off 0.0°C); AIFS ran 2°C cold.
  • Sun Aug 9 14 days out the models said 34–38; it hit 38. GEM led (off 0.3°C); AIFS ran 4°C cold.
  • Sat Aug 8 14 days out the models said 32–39; it hit 39. GFS led (off 0.6°C); GEM ran 3°C cold.
  • Fri Aug 7 14 days out the models said 32–39; it hit 40. GFS led (off 0.0°C); GEM ran 3°C cold.
  • Thu Aug 6 14 days out the models said 34–38; it hit 39. GFS led (off 0.2°C); GEM ran 3°C cold.
  • Wed Aug 5 14 days out the models said 34–41; it hit 35. GFS led (off 0.3°C); GEM ran 2°C cold.
  • Tue Aug 4 14 days out the models said 37–40; it hit 33. GFS led (off 0.3°C); GEM ran 3°C cold.
  • Mon Aug 3 14 days out the models said 32–41; it hit 33. GFS led (off 0.3°C); ICON ran 2°C cold.
  • Sun Aug 2 14 days out the models said 37–38; it hit 38. GFS led (off 0.2°C); ICON ran 2°C cold.
  • Sat Aug 1 14 days out the models said 33–37; it hit 40. ECMWF led (off 0.3°C); GEM ran 2°C cold.
  • Fri Jul 31 14 days out the models said 35–42; it hit 39. ECMWF led (off 0.1°C); GEM ran 2°C cold.
  • Thu Jul 30 13 days out the models said 34–42; it hit 35. GEM led (off 0.1°C); GFS ran 2°C hot.
  • Wed Jul 29 12 days out the models said 34–42; it hit 34. UKMO led (off 0.1°C); AIFS ran 4°C cold.
  • Tue Jul 28 11 days out the models said 31–39; it hit 35. UKMO led (off 0.3°C); AIFS ran 1°C cold.
  • Mon Jul 27 10 days out the models said 33–39; it hit 36. UKMO led (off 0.1°C); AIFS ran 2°C cold.
  • Sun Jul 26 9 days out the models said 30–39; it hit 39. GEM led (off 0.1°C); GFS ran 2°C hot.
  • Sat Jul 25 8 days out the models said 27–39; it hit 39. GEM led (off 0.3°C); UKMO ran 2°C cold.
  • Fri Jul 24 7 days out the models said 28–39; it hit 37. ECMWF led (off 0.0°C); AIFS ran 2°C cold.
  • Thu Jul 23 6 days out the models said 26–36; it hit 36. GFS led (off 0.1°C); UKMO ran 3°C cold.
  • Wed Jul 22 5 days out the models said 26–37; it hit 31. ECMWF led (off 0.1°C); AIFS ran 3°C cold.
  • Tue Jul 21 4 days out the models said 32–36; it hit 37. GFS led (off 0.1°C); AIGFS ran 3°C cold.
  • Mon Jul 20 3 days out the models said 36–39; it hit 39. ECMWF led (off 0.3°C); AIGFS ran 3°C cold.

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