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 9

KORD · gfs · lead 9

Target day = initialization date + 9 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
tmax00Zbilinear30d21 1 QC7.17 [5.67, 8.32]6.37-3.20 [-6.47, 0.59]8.34 [6.34, 9.56]5% [0%, 13%]10%10%-0.91-0.722026-08-10 → 2026-08-30
tmax00Zbilinear90d21 1 QC7.17 [5.37, 8.27]6.37-3.20 [-6.08, 1.05]8.34 [5.82, 9.49]5% [0%, 15%]10%10%-0.91-0.722026-08-10 → 2026-08-30
tmax00Zbilinear365d21 1 QC7.17 [5.23, 8.24]6.37-3.20 [-6.26, 1.49]8.34 [5.68, 9.41]5% [0%, 15%]10%10%-0.91-0.722026-08-10 → 2026-08-30
tmax00Zbilinearall21 1 QC7.17 [5.27, 8.28]6.37-3.20 [-6.77, 1.44]8.34 [5.68, 9.48]5% [0%, 15%]10%10%-0.91-0.722026-08-10 → 2026-08-30
tmax00Znearest30d21 1 QC7.03 [5.48, 8.26]6.26-3.30 [-6.61, 0.48]8.30 [6.11, 9.59]5% [0%, 13%]5%19%-0.87-0.692026-08-10 → 2026-08-30
tmax00Znearest90d21 1 QC7.03 [5.15, 8.19]6.26-3.30 [-6.25, 0.92]8.30 [5.56, 9.51]5% [0%, 15%]5%19%-0.87-0.692026-08-10 → 2026-08-30
tmax00Znearest365d21 1 QC7.03 [5.16, 8.19]6.26-3.30 [-6.43, 1.33]8.30 [5.56, 9.45]5% [0%, 15%]5%19%-0.87-0.692026-08-10 → 2026-08-30
tmax00Znearestall21 1 QC7.03 [5.05, 8.23]6.26-3.30 [-6.91, 1.40]8.30 [5.43, 9.55]5% [0%, 15%]5%19%-0.87-0.692026-08-10 → 2026-08-30
tmax12Zbilinear30d21 1 QC4.86 [3.82, 6.33]4.52-2.60 [-5.81, -0.16]5.89 [4.65, 7.58]5% [0%, 13%]33%33%-0.29-0.222026-08-10 → 2026-08-30
tmax12Zbilinear90d21 1 QC4.86 [3.75, 6.75]4.52-2.60 [-6.23, 0.02]5.89 [4.54, 8.04]5% [0%, 14%]33%33%-0.29-0.222026-08-10 → 2026-08-30
tmax12Zbilinear365d21 1 QC4.86 [3.68, 6.64]4.52-2.60 [-5.99, 0.15]5.89 [4.41, 7.88]5% [0%, 14%]33%33%-0.29-0.222026-08-10 → 2026-08-30
tmax12Zbilinearall21 1 QC4.86 [3.44, 6.70]4.52-2.60 [-6.16, 0.17]5.89 [4.30, 7.89]5% [0%, 14%]33%33%-0.29-0.222026-08-10 → 2026-08-30
tmax12Znearest30d21 1 QC4.40 [3.39, 5.79]4.17-2.35 [-5.33, -0.09]5.50 [4.34, 7.13]19% [0%, 31%]33%43%-0.17-0.132026-08-10 → 2026-08-30
tmax12Znearest90d21 1 QC4.40 [3.35, 6.23]4.17-2.35 [-5.75, 0.10]5.50 [4.18, 7.54]19% [0%, 29%]33%43%-0.17-0.132026-08-10 → 2026-08-30
tmax12Znearest365d21 1 QC4.40 [3.36, 6.11]4.17-2.35 [-5.73, 0.29]5.50 [4.13, 7.42]19% [0%, 29%]33%43%-0.17-0.132026-08-10 → 2026-08-30
tmax12Znearestall21 1 QC4.40 [3.10, 6.17]4.17-2.35 [-5.78, 0.29]5.50 [3.93, 7.41]19% [0%, 29%]33%43%-0.17-0.132026-08-10 → 2026-08-30
tmin00Zbilinear30d21 1 QC5.58 [4.01, 6.54]5.65-0.53 [-4.53, 3.56]6.47 [4.92, 7.34]10% [0%, 25%]14%29%-0.13-0.102026-08-10 → 2026-08-30
tmin00Zbilinear90d21 1 QC5.58 [3.49, 6.53]5.65-0.53 [-4.65, 3.79]6.47 [4.49, 7.31]10% [0%, 29%]14%29%-0.13-0.102026-08-10 → 2026-08-30
tmin00Zbilinear365d21 1 QC5.58 [3.70, 6.50]5.65-0.53 [-4.72, 3.96]6.47 [4.66, 7.32]10% [0%, 25%]14%29%-0.13-0.102026-08-10 → 2026-08-30
tmin00Zbilinearall21 1 QC5.58 [3.39, 6.60]5.65-0.53 [-4.99, 4.54]6.47 [4.36, 7.45]10% [0%, 26%]14%29%-0.13-0.102026-08-10 → 2026-08-30
tmin00Znearest30d21 1 QC5.57 [3.93, 6.65]5.67-0.85 [-4.88, 3.24]6.58 [4.92, 7.63]10% [0%, 25%]14%33%-0.13-0.112026-08-10 → 2026-08-30
tmin00Znearest90d21 1 QC5.57 [3.42, 6.59]5.67-0.85 [-4.98, 3.46]6.58 [4.47, 7.57]10% [0%, 29%]14%33%-0.13-0.112026-08-10 → 2026-08-30
tmin00Znearest365d21 1 QC5.57 [3.67, 6.63]5.67-0.85 [-5.08, 3.64]6.58 [4.52, 7.61]10% [0%, 25%]14%33%-0.13-0.112026-08-10 → 2026-08-30
tmin00Znearestall21 1 QC5.57 [3.25, 6.79]5.67-0.85 [-5.35, 4.24]6.58 [4.23, 7.74]10% [0%, 26%]14%33%-0.13-0.112026-08-10 → 2026-08-30
tmin12Zbilinear30d21 1 QC4.06 [2.46, 5.20]4.05+0.12 [-3.85, 3.23]5.34 [3.02, 6.36]10% [0%, 28%]38%48%+0.18+0.212026-08-10 → 2026-08-30
tmin12Zbilinear90d21 1 QC4.06 [1.86, 5.21]4.05+0.12 [-4.33, 3.29]5.34 [2.37, 6.28]10% [0%, 31%]38%48%+0.18+0.212026-08-10 → 2026-08-30
tmin12Zbilinear365d21 1 QC4.06 [1.85, 5.26]4.05+0.12 [-4.33, 3.46]5.34 [2.29, 6.27]10% [0%, 32%]38%48%+0.18+0.212026-08-10 → 2026-08-30
tmin12Zbilinearall21 1 QC4.06 [1.81, 5.25]4.05+0.12 [-4.34, 3.62]5.34 [2.12, 6.33]10% [0%, 31%]38%48%+0.18+0.212026-08-10 → 2026-08-30
tmin12Znearest30d21 1 QC4.17 [2.49, 5.45]4.19-0.35 [-4.33, 2.76]5.44 [2.98, 6.61]10% [0%, 28%]38%52%+0.16+0.182026-08-10 → 2026-08-30
tmin12Znearest90d21 1 QC4.17 [2.08, 5.52]4.19-0.35 [-4.82, 2.89]5.44 [2.66, 6.59]10% [0%, 31%]38%52%+0.16+0.182026-08-10 → 2026-08-30
tmin12Znearest365d21 1 QC4.17 [2.08, 5.61]4.19-0.35 [-4.82, 3.00]5.44 [2.47, 6.64]10% [0%, 32%]38%52%+0.16+0.182026-08-10 → 2026-08-30
tmin12Znearestall21 1 QC4.17 [1.88, 5.65]4.19-0.35 [-4.86, 3.10]5.44 [2.33, 6.71]10% [0%, 31%]38%52%+0.16+0.182026-08-10 → 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 9, 00Z bilinear tmax+20+100-10-202026-08-10: -3.6 °F2026-08-11: +9.08 °F2026-08-12: -12.95 °F2026-08-13: -0.45 °F2026-08-14: -9.91 °F2026-08-15: -6.96 °F2026-08-16: -15.54 °F2026-08-17: -5.87 °F2026-08-18: -3.48 °F2026-08-19: +7.56 °F2026-08-20: +7.44 °F2026-08-21: -3.53 °F2026-08-22: +1.38 °F2026-08-23: +6.95 °F2026-08-24: +6.23 °F2026-08-25: -5.21 °F2026-08-26: -18.01 °F2026-08-27: -9.35 °F2026-08-28: -8.33 °F2026-08-29: +3.02 °F2026-08-30: -5.73 °F2026-08-102026-08-30°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 (21 days, newest first) · download CSV
Climatological dayError °F
2026-08-30-5.73
2026-08-29+3.02
2026-08-28-8.33
2026-08-27-9.35
2026-08-26-18.01
2026-08-25-5.21
2026-08-24+6.23
2026-08-23+6.95
2026-08-22+1.38
2026-08-21-3.53
2026-08-20+7.44
2026-08-19+7.56
2026-08-18-3.48
2026-08-17-5.87
2026-08-16-15.54
2026-08-15-6.96
2026-08-14-9.91
2026-08-13-0.45
2026-08-12-12.95
2026-08-11+9.08
2026-08-10-3.60

Error distribution

Distribution of the signed daily error in °F for NCEP GFS at KORD, lead day 9-20 to -18 °F: 1 day-18 to -16 °F: 0 days-16 to -14 °F: 1 day-14 to -12 °F: 1 day-12 to -10 °F: 0 days-10 to -8 °F: 3 days-8 to -6 °F: 1 day-6 to -4 °F: 3 days-4 to -2 °F: 3 days-2 to 0 °F: 1 day0 to 2 °F: 1 day2 to 4 °F: 1 day4 to 6 °F: 0 days6 to 8 °F: 4 days8 to 10 °F: 1 day10 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| 6.95 · P90 |e| 12.95 °F-200+20 °Fn = 21 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
-20.00-18.001
-18.00-16.000
-16.00-14.001
-14.00-12.001
-12.00-10.000
-10.00-8.003
-8.00-6.001
-6.00-4.003
-4.00-2.003
-2.00+0.001
+0.00+2.001
+2.00+4.001
+4.00+6.000
+6.00+8.004
+8.00+10.001
+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
2026-08217.17 -3.20

Availability

ModelScored period DaysCoverage
NCEP GFS2026-08-10 → 2026-08-30 21
NCEP GFS2026-08-10 → 2026-08-30 21
NCEP GFS2026-08-10 → 2026-08-30 21
NCEP GFS2026-08-10 → 2026-08-30 21

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 21 +1.89 [0.36, 2.88] yes
GraphCast (IFS init) 21 +2.06 [-1.22, 3.42] no
ECMWF IFS HRES 16 +1.22 [-1.24, 2.95] no
Persistence (baseline) 21 +3.41 [0.44, 5.26] yes

Cite this page

ShortCastCheck, KORD gfs lead 9, methodology v0.2, accessed 2026-08-31, https://castcheck.zifanzhang.com/station/KORD/model/gfs/lead/9/

LongCastCheck (2026). Station-level verification of raw weather-model 2 m temperature forecasts: KORD (Chicago O'Hare), model gfs, lead day 9. 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/9/

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