Raw model output on the native 0.25° grid — no MOS, no bias correction, no post-processing. Scores understate operational forecast quality. Read the fairness statement →

CastCheck methodology v0.2 · data through 2026-08-30

Chicago O'Hare · NCEP GFS · lead day 3

KORD · gfs · lead 3

Target day = initialization date + 3 days. This page is a permanent link: the numbers change as history accumulates, the address and the methodology version do not.

Scores use the latest model version segment, gfs-0p25, starting 2026-08-01 — days before that ran a different version of the model and are excluded rather than silently pooled. Of the scored days, 1 carry a QC flag on the observation.

JSON for this page CSV of the daily errors Cite this page

Every number for this combination

All four windows × both initializations × both interpolations × both variables. Errors are computed in °C and shown in °F; CI is a 95 % moving-block bootstrap interval. MAE debiased and skill, debiased remove the constant offset of the window first, so a station that the model always reads a degree too warm is not scored as if it had no skill — compare the two skill columns to see how much of the error is a fixed offset. n QC next to n counts days whose observation carries a QC flag.

VariableInitMethod Windown MAE °F MAE debiased Bias °F RMSE °F ±1 °F±2 °F±3 °F Skill Skill, debiased Period
tmax00Zbilinear30d27 1 QC3.92 [3.00, 4.90]3.87-1.27 [-2.51, -0.01]4.81 [3.81, 5.77]15% [0%, 30%]22%48%-0.29-0.242026-08-04 → 2026-08-30
tmax00Zbilinear90d27 1 QC3.92 [2.96, 4.89]3.87-1.27 [-2.57, 0.07]4.81 [3.81, 5.76]15% [0%, 30%]22%48%-0.29-0.242026-08-04 → 2026-08-30
tmax00Zbilinear365d27 1 QC3.92 [2.89, 4.99]3.87-1.27 [-2.58, 0.21]4.81 [3.70, 5.78]15% [0%, 31%]22%48%-0.29-0.242026-08-04 → 2026-08-30
tmax00Zbilinearall27 1 QC3.92 [2.84, 4.94]3.87-1.27 [-2.57, 0.20]4.81 [3.62, 5.80]15% [0%, 31%]22%48%-0.29-0.242026-08-04 → 2026-08-30
tmax00Znearest30d27 1 QC3.85 [2.99, 4.69]3.78-0.86 [-2.04, 0.38]4.69 [3.72, 5.56]15% [7%, 26%]33%44%-0.27-0.212026-08-04 → 2026-08-30
tmax00Znearest90d27 1 QC3.85 [2.93, 4.68]3.78-0.86 [-2.05, 0.50]4.69 [3.68, 5.54]15% [3%, 27%]33%44%-0.27-0.212026-08-04 → 2026-08-30
tmax00Znearest365d27 1 QC3.85 [2.78, 4.75]3.78-0.86 [-2.08, 0.55]4.69 [3.58, 5.62]15% [3%, 29%]33%44%-0.27-0.212026-08-04 → 2026-08-30
tmax00Znearestall27 1 QC3.85 [2.74, 4.77]3.78-0.86 [-2.06, 0.63]4.69 [3.53, 5.64]15% [3%, 29%]33%44%-0.27-0.212026-08-04 → 2026-08-30
tmax12Zbilinear30d27 1 QC2.52 [1.62, 3.42]2.57+0.24 [-0.84, 1.36]3.51 [2.24, 4.56]37% [18%, 57%]59%70%+0.17+0.182026-08-04 → 2026-08-30
tmax12Zbilinear90d27 1 QC2.52 [1.61, 3.59]2.57+0.24 [-1.05, 1.43]3.51 [2.12, 4.62]37% [14%, 57%]59%70%+0.17+0.182026-08-04 → 2026-08-30
tmax12Zbilinear365d27 1 QC2.52 [1.43, 3.84]2.57+0.24 [-1.09, 1.45]3.51 [1.81, 4.82]37% [15%, 57%]59%70%+0.17+0.182026-08-04 → 2026-08-30
tmax12Zbilinearall27 1 QC2.52 [1.44, 3.61]2.57+0.24 [-1.04, 1.45]3.51 [1.79, 4.76]37% [12%, 57%]59%70%+0.17+0.182026-08-04 → 2026-08-30
tmax12Znearest30d27 1 QC2.73 [1.86, 3.63]2.82+0.32 [-0.98, 1.66]3.76 [2.54, 4.81]41% [25%, 55%]52%67%+0.10+0.092026-08-04 → 2026-08-30
tmax12Znearest90d27 1 QC2.73 [1.78, 3.83]2.82+0.32 [-1.22, 1.76]3.76 [2.35, 4.86]41% [21%, 54%]52%67%+0.10+0.092026-08-04 → 2026-08-30
tmax12Znearest365d27 1 QC2.73 [1.72, 3.93]2.82+0.32 [-1.45, 1.77]3.76 [2.25, 5.04]41% [22%, 55%]52%67%+0.10+0.092026-08-04 → 2026-08-30
tmax12Znearestall27 1 QC2.73 [1.68, 3.78]2.82+0.32 [-1.27, 1.72]3.76 [2.20, 4.95]41% [21%, 57%]52%67%+0.10+0.092026-08-04 → 2026-08-30
tmin00Zbilinear30d27 1 QC2.27 [1.52, 3.17]2.23+0.79 [-0.27, 1.73]2.91 [1.94, 3.79]26% [12%, 40%]52%78%+0.41+0.422026-08-04 → 2026-08-30
tmin00Zbilinear90d27 1 QC2.27 [1.50, 3.09]2.23+0.79 [-0.42, 1.80]2.91 [1.81, 3.77]26% [12%, 39%]52%78%+0.41+0.422026-08-04 → 2026-08-30
tmin00Zbilinear365d27 1 QC2.27 [1.47, 3.19]2.23+0.79 [-0.43, 1.82]2.91 [1.81, 3.89]26% [10%, 41%]52%78%+0.41+0.422026-08-04 → 2026-08-30
tmin00Zbilinearall27 1 QC2.27 [1.48, 3.32]2.23+0.79 [-0.53, 1.82]2.91 [1.78, 3.91]26% [7%, 43%]52%78%+0.41+0.422026-08-04 → 2026-08-30
tmin00Znearest30d27 1 QC2.18 [1.55, 2.97]2.19+0.39 [-0.64, 1.28]2.80 [1.90, 3.68]26% [16%, 37%]56%78%+0.43+0.432026-08-04 → 2026-08-30
tmin00Znearest90d27 1 QC2.18 [1.55, 2.90]2.19+0.39 [-0.78, 1.35]2.80 [1.85, 3.67]26% [15%, 36%]56%78%+0.43+0.432026-08-04 → 2026-08-30
tmin00Znearest365d27 1 QC2.18 [1.49, 2.96]2.19+0.39 [-0.81, 1.38]2.80 [1.81, 3.76]26% [14%, 36%]56%78%+0.43+0.432026-08-04 → 2026-08-30
tmin00Znearestall27 1 QC2.18 [1.52, 3.07]2.19+0.39 [-0.89, 1.32]2.80 [1.82, 3.78]26% [14%, 36%]56%78%+0.43+0.432026-08-04 → 2026-08-30
tmin12Zbilinear30d27 1 QC2.51 [1.93, 3.12]2.24+1.02 [-0.27, 2.00]2.92 [2.34, 3.44]15% [0%, 30%]44%67%+0.35+0.422026-08-04 → 2026-08-30
tmin12Zbilinear90d27 1 QC2.51 [1.81, 3.14]2.24+1.02 [-0.42, 2.13]2.92 [2.28, 3.48]15% [0%, 33%]44%67%+0.35+0.422026-08-04 → 2026-08-30
tmin12Zbilinear365d27 1 QC2.51 [1.81, 3.17]2.24+1.02 [-0.33, 2.15]2.92 [2.20, 3.50]15% [0%, 36%]44%67%+0.35+0.422026-08-04 → 2026-08-30
tmin12Zbilinearall27 1 QC2.51 [1.79, 3.26]2.24+1.02 [-0.59, 2.24]2.92 [2.23, 3.58]15% [0%, 35%]44%67%+0.35+0.422026-08-04 → 2026-08-30
tmin12Znearest30d27 1 QC2.37 [1.78, 2.92]2.26+0.59 [-0.64, 1.50]2.80 [2.27, 3.25]22% [7%, 41%]41%70%+0.38+0.422026-08-04 → 2026-08-30
tmin12Znearest90d27 1 QC2.37 [1.71, 3.00]2.26+0.59 [-0.78, 1.59]2.80 [2.21, 3.30]22% [3%, 43%]41%70%+0.38+0.422026-08-04 → 2026-08-30
tmin12Znearest365d27 1 QC2.37 [1.61, 3.03]2.26+0.59 [-0.78, 1.65]2.80 [2.10, 3.32]22% [0%, 44%]41%70%+0.38+0.422026-08-04 → 2026-08-30
tmin12Znearestall27 1 QC2.37 [1.60, 3.16]2.26+0.59 [-0.94, 1.70]2.80 [2.17, 3.39]22% [0%, 46%]41%70%+0.38+0.422026-08-04 → 2026-08-30

+ model too warm · − model too cold · bias interval includes zero · ★ lowest MAE · = not distinguishable from the leader · ▼ significantly worse · n < 30 greyed and unranked · CI is a 95 % moving-block bootstrap interval.

Daily error, last 90 days

Daily forecast minus observed error in °F for NCEP GFS at KORD, lead day 3, 00Z bilinear tmax+20+100-10-202026-08-04: -2.02 °F2026-08-05: +2.13 °F2026-08-06: -7.96 °F2026-08-07: -2.43 °F2026-08-08: +4.47 °F2026-08-09: -10.72 °F2026-08-10: -7.87 °F2026-08-11: +3.64 °F2026-08-12: -1.13 °F2026-08-13: +2.41 °F2026-08-14: -3.61 °F2026-08-15: +7.99 °F2026-08-16: -4.84 °F2026-08-17: +2.11 °F2026-08-18: +0.16 °F2026-08-19: -7.93 °F2026-08-20: +3.98 °F2026-08-21: +2.16 °F2026-08-22: -0.67 °F2026-08-23: -1.61 °F2026-08-24: -0.3 °F2026-08-25: -5.93 °F2026-08-26: -5.56 °F2026-08-27: -0.47 °F2026-08-28: -6.97 °F2026-08-29: +2.78 °F2026-08-30: +3.96 °F2026-08-042026-08-30°F, forecast − observed
Forecast − observed, °F, 00Z bilinear daily maximum. The dashed line is zero; the thick line is a centred 7-day mean, drawn only where the whole window is present. Gaps are days with no score, never interpolation. Hover a point for its date and value.
The same series as a table (27 days, newest first) · download CSV
Climatological dayError °F
2026-08-30+3.96
2026-08-29+2.78
2026-08-28-6.97
2026-08-27-0.47
2026-08-26-5.56
2026-08-25-5.93
2026-08-24-0.30
2026-08-23-1.61
2026-08-22-0.67
2026-08-21+2.16
2026-08-20+3.98
2026-08-19-7.93
2026-08-18+0.16
2026-08-17+2.11
2026-08-16-4.84
2026-08-15+7.99
2026-08-14-3.61
2026-08-13+2.41
2026-08-12-1.13
2026-08-11+3.64
2026-08-10-7.87
2026-08-09-10.72
2026-08-08+4.47
2026-08-07-2.43
2026-08-06-7.96
2026-08-05+2.13
2026-08-04-2.02

Error distribution

Distribution of the signed daily error in °F for NCEP GFS at KORD, lead day 3-20 to -18 °F: 0 days-18 to -16 °F: 0 days-16 to -14 °F: 0 days-14 to -12 °F: 0 days-12 to -10 °F: 1 day-10 to -8 °F: 0 days-8 to -6 °F: 4 days-6 to -4 °F: 3 days-4 to -2 °F: 3 days-2 to 0 °F: 5 days0 to 2 °F: 1 day2 to 4 °F: 8 days4 to 6 °F: 1 day6 to 8 °F: 1 day8 to 10 °F: 0 days10 to 12 °F: 0 days12 to 14 °F: 0 days14 to 16 °F: 0 days16 to 18 °F: 0 days18 to 20 °F: 0 daysdashed: P50 |e| 3.61 · P90 |e| 7.94 °F-200+20 °Fn = 27 days
All scored days for 00Z bilinear daily maximum, 20 equal bins. The dashed marks are the 50th and 90th percentiles of the absolute error, mirrored on both sides. Hover a bar for its bin and count.
Bin counts as a table
From °FTo °FDays
-20.00-18.000
-18.00-16.000
-16.00-14.000
-14.00-12.000
-12.00-10.001
-10.00-8.000
-8.00-6.004
-6.00-4.003
-4.00-2.003
-2.00+0.005
+0.00+2.001
+2.00+4.008
+4.00+6.001
+6.00+8.001
+8.00+10.000
+10.00+12.000
+12.00+14.000
+14.00+16.000
+16.00+18.000
+18.00+20.000

Month by month

00Z bilinear daily maximum, newest first.

Monthn MAE °FBias °F
2026-08273.92 -1.27

Availability

ModelScored period DaysCoverage
NCEP GFS2026-08-04 → 2026-08-30 27
NCEP GFS2026-08-04 → 2026-08-30 27
NCEP GFS2026-08-04 → 2026-08-30 27
NCEP GFS2026-08-04 → 2026-08-30 27

Compared with other models

Paired bootstrap on the days both models cover (90d, 00Z, bilinear, daily maximum). Negative means NCEP GFS has the lower MAE. "Distinguishable" means the 95 % interval excludes zero.

Other modelCommon days MAE difference °FDistinguishable
ECMWF AIFS Single 27 +0.26 [-0.65, 1.41] no
GraphCast (IFS init) 25 -0.01 [-1.48, 1.16] no
ECMWF IFS HRES 22 +0.93 [-0.35, 1.90] no
Persistence (baseline) 27 +0.88 [-0.72, 2.39] no

Cite this page

ShortCastCheck, KORD gfs lead 3, methodology v0.2, accessed 2026-08-31, https://castcheck.zifanzhang.com/station/KORD/model/gfs/lead/3/

LongCastCheck (2026). Station-level verification of raw weather-model 2 m temperature forecasts: KORD (Chicago O'Hare), model gfs, lead day 3. Methodology version 0.2, schema version 0.1, data through 2026-08-30. Accessed 2026-08-31. https://castcheck.zifanzhang.com/station/KORD/model/gfs/lead/3/

Accessed2026-08-31 (data through 2026-08-30; page built 2026-08-31T03:52:06+00:00)

JSON CSV all scores methodology v0.2 licence