The Spread

Which weather model is most accurate in Salt Lake City?

Outlook Model accuracy

Salt Lake City, Utah · 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 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 4.15°F at 1-day lead over this window.

The Spread's own bias-corrected blend scored a 1.01°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 2.0° (-1.2°) 2.4° (-1.6°) — 30
NOAA GFS 2.0° (-0.3°) 2.2° (+0.5°) 5.3° (+2.0°) 30
GEM (Canada) 2.2° (-1.4°) 4.2° (-3.0°) 4.3° (-1.9°) 30
NOAA AIGFS (AI) 2.6° (-2.5°) 3.2° (-2.9°) 5.3° (-4.1°) 30
ECMWF IFS 2.9° (-2.6°) 2.5° (-1.4°) 4.5° (+1.8°) 30
UKMO (UK) 2.9° (-2.5°) 2.9° (-2.1°) — 30
ECMWF AIFS (AI) 4.2° (-4.2°) 3.9° (-3.9°) 5.2° (-4.4°) 30
NBM (US blend) 2.9° (-2.8°) 3.1° (-2.8°) 5.8° (-2.2°) 30
Blended (bias-corrected) 1.0° (+0.0°) 1.4° (-0.0°) 3.2° (-0.0°) 30

Method, honestly

The Spread's Salt Lake City point is the Salt Lake City Intl station (SLC), 4.4 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 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 84–99; it hit 84. GFS led (off 0.9°F); UKMO ran 6°F cold.
  • Mon Aug 31 11 days out the models said 82–96; it hit 87. GFS led (off 1.7°F); AIFS ran 10°F cold.
  • Sun Aug 30 10 days out the models said 78–91; it hit 82. GFS led (off 0.9°F); ECMWF ran 9°F cold.
  • Sat Aug 29 9 days out the models said 78–101; it hit 75. ECMWF led (off 0.0°F); GFS ran 9°F hot.
  • Fri Aug 28 8 days out the models said 79–98; it hit 92. UKMO led (off 0.1°F); AIFS ran 9°F cold.
  • Thu Aug 27 7 days out the models said 89–96; it hit 97. ICON led (off 0.3°F); AIFS ran 7°F cold.
  • Wed Aug 26 6 days out the models said 91–97; it hit 96. GFS led (off 0.3°F); AIFS ran 4°F cold.
  • Tue Aug 25 5 days out the models said 89–96; it hit 94. GEM led (off 0.4°F); AIFS ran 3°F cold.
  • Mon Aug 24 4 days out the models said 89–95; it hit 95. ICON led (off 0.0°F); AIFS ran 9°F cold.
  • Sun Aug 23 3 days out the models said 92–96; it hit 94. ICON led (off 0.1°F); AIFS ran 6°F cold.
  • Tue Aug 18 14 days out the models said 73–96; it hit 94. ICON led (off 0.0°F).
  • Mon Aug 17 14 days out the models said 75–97; it hit 96. GEM led (off 0.0°F); UKMO ran 4°F cold.
  • Sun Aug 16 14 days out the models said 73–100; it hit 91. GEM led (off 0.8°F); UKMO ran 3°F cold.
  • Sat Aug 15 14 days out the models said 82–92; it hit 83. UKMO led (off 0.3°F); GFS ran 4°F hot.
  • Fri Aug 14 14 days out the models said 84–100; it hit 78. UKMO led (off 0.6°F); GFS ran 5°F hot.
  • Thu Aug 13 14 days out the models said 82–100; it hit 75. GEM led (off 0.1°F); AIGFS ran 4°F hot.
  • Wed Aug 12 14 days out the models said 79–100; it hit 88. GFS led (off 0.3°F); AIFS ran 8°F cold.
  • Tue Aug 11 14 days out the models said 83–100; it hit 97. ECMWF led (off 0.3°F); AIFS ran 6°F cold.
  • Mon Aug 10 14 days out the models said 90–99; it hit 98. AIGFS led (off 0.0°F); AIFS ran 3°F cold.
  • Sun Aug 9 14 days out the models said 93–100; it hit 100. GEM led (off 0.5°F); AIFS ran 7°F cold.
  • Sat Aug 8 14 days out the models said 89–102; it hit 103. GFS led (off 1.0°F); GEM ran 6°F cold.
  • Fri Aug 7 14 days out the models said 90–102; it hit 104. GFS led (off 0.0°F); GEM ran 6°F cold.
  • Thu Aug 6 14 days out the models said 94–100; it hit 101. GFS led (off 0.4°F); GEM ran 6°F cold.
  • Wed Aug 5 14 days out the models said 93–106; it hit 95. GFS led (off 0.5°F); GEM ran 4°F cold.
  • Tue Aug 4 14 days out the models said 98–103; it hit 91. GFS led (off 0.5°F); GEM ran 5°F cold.
  • Mon Aug 3 14 days out the models said 90–105; it hit 91. GFS led (off 0.6°F); ICON ran 3°F cold.
  • Sun Aug 2 14 days out the models said 99–101; it hit 101. GFS led (off 0.3°F); ICON ran 4°F cold.
  • Sat Aug 1 14 days out the models said 92–99; it hit 105. ECMWF led (off 0.6°F); GEM ran 4°F cold.
  • Fri Jul 31 14 days out the models said 94–108; it hit 102. ECMWF led (off 0.1°F); GEM ran 4°F cold.
  • Thu Jul 30 13 days out the models said 93–108; it hit 95. GEM led (off 0.1°F); GFS ran 4°F hot.
  • Wed Jul 29 12 days out the models said 94–107; it hit 93. UKMO led (off 0.1°F); AIFS ran 7°F cold.
  • Tue Jul 28 11 days out the models said 88–103; it hit 95. UKMO led (off 0.6°F); AIFS ran 2°F cold.
  • Mon Jul 27 10 days out the models said 92–102; it hit 96. UKMO led (off 0.1°F); AIFS ran 4°F cold.
  • Sun Jul 26 9 days out the models said 85–101; it hit 101. GEM led (off 0.2°F); GFS ran 3°F hot.
  • Sat Jul 25 8 days out the models said 81–102; it hit 102. GEM led (off 0.6°F); UKMO ran 4°F cold.
  • Fri Jul 24 7 days out the models said 82–103; it hit 99. ECMWF led (off 0.0°F); AIFS ran 3°F cold.
  • Thu Jul 23 6 days out the models said 78–96; it hit 96. GFS led (off 0.2°F); UKMO ran 5°F cold.
  • Wed Jul 22 5 days out the models said 80–98; it hit 87. ECMWF led (off 0.2°F); AIFS ran 5°F cold.
  • Tue Jul 21 4 days out the models said 89–98; it hit 99. GFS led (off 0.1°F); AIGFS ran 6°F cold.
  • Mon Jul 20 3 days out the models said 96–102; it hit 102. ECMWF led (off 0.6°F); AIGFS ran 6°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.