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 6

KORD · gfs · lead 6

Target day = initialization date + 6 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
tmax00Zbilinear30d24 1 QC2.84 [2.17, 3.61]2.73-1.04 [-2.32, 0.45]3.58 [2.68, 4.42]17% [4%, 33%]50%58%+0.16+0.182026-08-07 → 2026-08-30
tmax00Zbilinear90d24 1 QC2.84 [2.12, 3.72]2.73-1.04 [-2.31, 0.52]3.58 [2.60, 4.53]17% [0%, 36%]50%58%+0.16+0.182026-08-07 → 2026-08-30
tmax00Zbilinear365d24 1 QC2.84 [2.04, 3.82]2.73-1.04 [-2.41, 0.66]3.58 [2.58, 4.62]17% [0%, 33%]50%58%+0.16+0.182026-08-07 → 2026-08-30
tmax00Zbilinearall24 1 QC2.84 [2.08, 3.76]2.73-1.04 [-2.42, 0.70]3.58 [2.49, 4.55]17% [0%, 36%]50%58%+0.16+0.182026-08-07 → 2026-08-30
tmax00Znearest30d24 1 QC2.61 [1.99, 3.36]2.53-1.06 [-2.04, 0.11]3.41 [2.45, 4.28]25% [7%, 44%]46%67%+0.23+0.242026-08-07 → 2026-08-30
tmax00Znearest90d24 1 QC2.61 [1.95, 3.45]2.53-1.06 [-2.02, 0.18]3.41 [2.38, 4.41]25% [2%, 50%]46%67%+0.23+0.242026-08-07 → 2026-08-30
tmax00Znearest365d24 1 QC2.61 [1.91, 3.59]2.53-1.06 [-2.13, 0.27]3.41 [2.35, 4.50]25% [0%, 46%]46%67%+0.23+0.242026-08-07 → 2026-08-30
tmax00Znearestall24 1 QC2.61 [1.84, 3.49]2.53-1.06 [-2.11, 0.31]3.41 [2.25, 4.42]25% [0%, 50%]46%67%+0.23+0.242026-08-07 → 2026-08-30
tmax12Zbilinear30d24 1 QC3.20 [2.50, 4.09]3.17-1.17 [-2.07, -0.25]4.12 [3.34, 4.83]29% [11%, 47%]42%50%+0.05+0.052026-08-07 → 2026-08-30
tmax12Zbilinear90d24 1 QC3.20 [2.47, 4.10]3.17-1.17 [-2.11, -0.17]4.12 [3.16, 4.81]29% [6%, 48%]42%50%+0.05+0.052026-08-07 → 2026-08-30
tmax12Zbilinear365d24 1 QC3.20 [2.41, 4.20]3.17-1.17 [-2.18, -0.11]4.12 [3.14, 4.90]29% [6%, 50%]42%50%+0.05+0.052026-08-07 → 2026-08-30
tmax12Zbilinearall24 1 QC3.20 [2.42, 4.16]3.17-1.17 [-2.13, -0.12]4.12 [3.19, 4.89]29% [0%, 48%]42%50%+0.05+0.052026-08-07 → 2026-08-30
tmax12Znearest30d24 1 QC3.20 [2.60, 3.98]3.04-1.52 [-2.36, -0.66]4.07 [3.33, 4.79]33% [17%, 50%]42%58%+0.05+0.092026-08-07 → 2026-08-30
tmax12Znearest90d24 1 QC3.20 [2.61, 4.05]3.04-1.52 [-2.44, -0.68]4.07 [3.24, 4.75]33% [10%, 50%]42%58%+0.05+0.092026-08-07 → 2026-08-30
tmax12Znearest365d24 1 QC3.20 [2.56, 4.06]3.04-1.52 [-2.41, -0.52]4.07 [3.17, 4.81]33% [11%, 51%]42%58%+0.05+0.092026-08-07 → 2026-08-30
tmax12Znearestall24 1 QC3.20 [2.59, 4.05]3.04-1.52 [-2.44, -0.60]4.07 [3.20, 4.86]33% [10%, 50%]42%58%+0.05+0.092026-08-07 → 2026-08-30
tmin00Zbilinear30d24 1 QC3.94 [2.94, 4.78]3.98+0.62 [-2.02, 2.87]4.97 [3.69, 5.88]12% [0%, 24%]21%54%+0.12+0.112026-08-07 → 2026-08-30
tmin00Zbilinear90d24 1 QC3.94 [2.47, 4.73]3.98+0.62 [-2.18, 3.04]4.97 [2.85, 5.94]12% [0%, 25%]21%54%+0.12+0.112026-08-07 → 2026-08-30
tmin00Zbilinear365d24 1 QC3.94 [2.52, 4.91]3.98+0.62 [-2.32, 3.07]4.97 [2.98, 6.04]12% [0%, 27%]21%54%+0.12+0.112026-08-07 → 2026-08-30
tmin00Zbilinearall24 1 QC3.94 [2.44, 4.87]3.98+0.62 [-2.35, 3.40]4.97 [2.46, 5.98]12% [0%, 25%]21%54%+0.12+0.112026-08-07 → 2026-08-30
tmin00Znearest30d24 1 QC4.01 [2.99, 4.86]4.02+0.17 [-2.51, 2.48]5.00 [3.65, 5.95]8% [0%, 16%]25%50%+0.10+0.102026-08-07 → 2026-08-30
tmin00Znearest90d24 1 QC4.01 [2.58, 4.84]4.02+0.17 [-2.70, 2.66]5.00 [2.80, 6.03]8% [0%, 17%]25%50%+0.10+0.102026-08-07 → 2026-08-30
tmin00Znearest365d24 1 QC4.01 [2.66, 5.01]4.02+0.17 [-2.83, 2.68]5.00 [2.92, 6.17]8% [0%, 17%]25%50%+0.10+0.102026-08-07 → 2026-08-30
tmin00Znearestall24 1 QC4.01 [2.57, 4.90]4.02+0.17 [-2.84, 2.98]5.00 [2.74, 6.00]8% [0%, 16%]25%50%+0.10+0.102026-08-07 → 2026-08-30
tmin12Zbilinear30d24 1 QC2.99 [2.02, 3.97]2.84+1.21 [-0.79, 3.19]4.16 [2.71, 5.49]33% [18%, 48%]42%58%+0.33+0.372026-08-07 → 2026-08-30
tmin12Zbilinear90d24 1 QC2.99 [1.77, 4.04]2.84+1.21 [-0.82, 3.45]4.16 [2.21, 5.64]33% [16%, 50%]42%58%+0.33+0.372026-08-07 → 2026-08-30
tmin12Zbilinear365d24 1 QC2.99 [1.77, 4.25]2.84+1.21 [-0.86, 3.41]4.16 [2.27, 5.73]33% [14%, 50%]42%58%+0.33+0.372026-08-07 → 2026-08-30
tmin12Zbilinearall24 1 QC2.99 [1.60, 4.06]2.84+1.21 [-1.13, 3.43]4.16 [2.13, 5.65]33% [12%, 50%]42%58%+0.33+0.372026-08-07 → 2026-08-30
tmin12Znearest30d24 1 QC2.90 [1.91, 3.87]2.85+0.78 [-1.26, 2.80]4.08 [2.64, 5.40]25% [9%, 41%]46%62%+0.35+0.362026-08-07 → 2026-08-30
tmin12Znearest90d24 1 QC2.90 [1.57, 3.91]2.85+0.78 [-1.26, 3.14]4.08 [2.02, 5.48]25% [7%, 45%]46%62%+0.35+0.362026-08-07 → 2026-08-30
tmin12Znearest365d24 1 QC2.90 [1.56, 4.07]2.85+0.78 [-1.34, 3.01]4.08 [2.03, 5.73]25% [6%, 46%]46%62%+0.35+0.362026-08-07 → 2026-08-30
tmin12Znearestall24 1 QC2.90 [1.41, 3.97]2.85+0.78 [-1.55, 3.05]4.08 [1.89, 5.52]25% [0%, 45%]46%62%+0.35+0.362026-08-07 → 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 6, 00Z bilinear tmax+10+50-5-102026-08-07: +0.02 °F2026-08-08: +1.44 °F2026-08-09: +6.22 °F2026-08-10: -7.74 °F2026-08-11: -5.37 °F2026-08-12: -3.14 °F2026-08-13: -0.8 °F2026-08-14: -5.14 °F2026-08-15: -0.53 °F2026-08-16: -1.94 °F2026-08-17: -4.14 °F2026-08-18: +0.08 °F2026-08-19: -7.09 °F2026-08-20: +1.12 °F2026-08-21: +1.11 °F2026-08-22: -1.24 °F2026-08-23: -2.01 °F2026-08-24: +2.23 °F2026-08-25: +4.1 °F2026-08-26: +1.59 °F2026-08-27: -1.82 °F2026-08-28: -1.27 °F2026-08-29: -4.38 °F2026-08-30: +3.7 °F2026-08-072026-08-30°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 (24 days, newest first) · download CSV
Climatological dayError °F
2026-08-30+3.70
2026-08-29-4.38
2026-08-28-1.27
2026-08-27-1.82
2026-08-26+1.59
2026-08-25+4.10
2026-08-24+2.23
2026-08-23-2.01
2026-08-22-1.24
2026-08-21+1.11
2026-08-20+1.12
2026-08-19-7.09
2026-08-18+0.08
2026-08-17-4.14
2026-08-16-1.94
2026-08-15-0.53
2026-08-14-5.14
2026-08-13-0.80
2026-08-12-3.14
2026-08-11-5.37
2026-08-10-7.74
2026-08-09+6.22
2026-08-08+1.44
2026-08-07+0.02

Error distribution

Distribution of the signed daily error in °F for NCEP GFS at KORD, lead day 6-10 to -9 °F: 0 days-9 to -8 °F: 0 days-8 to -7 °F: 2 days-7 to -6 °F: 0 days-6 to -5 °F: 2 days-5 to -4 °F: 2 days-4 to -3 °F: 1 day-3 to -2 °F: 1 day-2 to -1 °F: 4 days-1 to 0 °F: 2 days0 to 1 °F: 2 days1 to 2 °F: 4 days2 to 3 °F: 1 day3 to 4 °F: 1 day4 to 5 °F: 1 day5 to 6 °F: 0 days6 to 7 °F: 1 day7 to 8 °F: 0 days8 to 9 °F: 0 days9 to 10 °F: 0 daysdashed: P50 |e| 1.97 · P90 |e| 5.96 °F-100+10 °Fn = 24 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
-10.00-9.000
-9.00-8.000
-8.00-7.002
-7.00-6.000
-6.00-5.002
-5.00-4.002
-4.00-3.001
-3.00-2.001
-2.00-1.004
-1.00+0.002
+0.00+1.002
+1.00+2.004
+2.00+3.001
+3.00+4.001
+4.00+5.001
+5.00+6.000
+6.00+7.001
+7.00+8.000
+8.00+9.000
+9.00+10.000

Month by month

00Z bilinear daily maximum, newest first.

Monthn MAE °FBias °F
2026-08242.84 -1.04

Availability

ModelScored period DaysCoverage
NCEP GFS2026-08-07 → 2026-08-30 24
NCEP GFS2026-08-07 → 2026-08-30 24
NCEP GFS2026-08-07 → 2026-08-30 24
NCEP GFS2026-08-07 → 2026-08-30 24

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 24 -1.40 [-2.94, -0.07] yes
GraphCast (IFS init) 24 -1.25 [-2.99, 0.06] no
ECMWF IFS HRES 19 -1.11 [-2.27, -0.15] yes
Persistence (baseline) 24 -0.53 [-2.56, 0.34] no

Cite this page

ShortCastCheck, KORD gfs lead 6, methodology v0.2, accessed 2026-08-31, https://castcheck.zifanzhang.com/station/KORD/model/gfs/lead/6/

LongCastCheck (2026). Station-level verification of raw weather-model 2 m temperature forecasts: KORD (Chicago O'Hare), model gfs, lead day 6. 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/6/

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