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

Chicago O'Hare · NCEP GFS · lead day 4

KORD · gfs · lead 4

Target day = initialization date + 4 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
tmax00Zbilinear30d26 1 QC3.15 [1.72, 4.65]3.26-1.15 [-2.75, 0.53]4.34 [2.42, 6.01]27% [5%, 57%]38%58%-0.02-0.072026-08-05 → 2026-08-30
tmax00Zbilinear90d26 1 QC3.15 [1.58, 4.92]3.26-1.15 [-2.88, 0.75]4.34 [2.24, 6.18]27% [0%, 58%]38%58%-0.02-0.072026-08-05 → 2026-08-30
tmax00Zbilinear365d26 1 QC3.15 [1.43, 4.98]3.26-1.15 [-2.91, 0.80]4.34 [2.08, 6.18]27% [0%, 62%]38%58%-0.02-0.072026-08-05 → 2026-08-30
tmax00Zbilinearall26 1 QC3.15 [1.46, 5.01]3.26-1.15 [-3.01, 0.89]4.34 [2.12, 6.28]27% [0%, 60%]38%58%-0.02-0.072026-08-05 → 2026-08-30
tmax00Znearest30d26 1 QC2.97 [1.73, 4.46]2.93-0.94 [-2.26, 0.48]4.18 [2.35, 5.89]27% [0%, 61%]50%62%+0.03+0.042026-08-05 → 2026-08-30
tmax00Znearest90d26 1 QC2.97 [1.69, 4.71]2.93-0.94 [-2.38, 0.59]4.18 [2.28, 6.02]27% [0%, 64%]50%62%+0.03+0.042026-08-05 → 2026-08-30
tmax00Znearest365d26 1 QC2.97 [1.59, 4.74]2.93-0.94 [-2.41, 0.63]4.18 [2.19, 6.03]27% [0%, 66%]50%62%+0.03+0.042026-08-05 → 2026-08-30
tmax00Znearestall26 1 QC2.97 [1.65, 4.77]2.93-0.94 [-2.52, 0.70]4.18 [2.25, 6.13]27% [0%, 67%]50%62%+0.03+0.042026-08-05 → 2026-08-30
tmax12Zbilinear30d26 1 QC3.04 [2.03, 4.13]2.91-1.16 [-2.16, -0.08]3.80 [2.40, 5.02]23% [11%, 36%]31%58%+0.01+0.052026-08-05 → 2026-08-30
tmax12Zbilinear90d26 1 QC3.04 [1.88, 4.33]2.91-1.16 [-2.23, 0.06]3.80 [2.23, 5.16]23% [9%, 40%]31%58%+0.01+0.052026-08-05 → 2026-08-30
tmax12Zbilinear365d26 1 QC3.04 [1.86, 4.32]2.91-1.16 [-2.20, 0.22]3.80 [2.19, 5.23]23% [9%, 43%]31%58%+0.01+0.052026-08-05 → 2026-08-30
tmax12Zbilinearall26 1 QC3.04 [1.87, 4.40]2.91-1.16 [-2.29, 0.29]3.80 [2.19, 5.26]23% [7%, 40%]31%58%+0.01+0.052026-08-05 → 2026-08-30
tmax12Znearest30d26 1 QC2.72 [1.62, 3.93]2.66-1.07 [-1.89, -0.16]3.59 [2.15, 4.79]27% [7%, 48%]42%65%+0.12+0.132026-08-05 → 2026-08-30
tmax12Znearest90d26 1 QC2.72 [1.49, 4.14]2.66-1.07 [-1.98, -0.07]3.59 [2.02, 4.97]27% [6%, 52%]42%65%+0.12+0.132026-08-05 → 2026-08-30
tmax12Znearest365d26 1 QC2.72 [1.43, 4.10]2.66-1.07 [-1.91, 0.10]3.59 [1.92, 5.02]27% [5%, 56%]42%65%+0.12+0.132026-08-05 → 2026-08-30
tmax12Znearestall26 1 QC2.72 [1.53, 4.19]2.66-1.07 [-2.00, 0.10]3.59 [2.05, 5.03]27% [0%, 50%]42%65%+0.12+0.132026-08-05 → 2026-08-30
tmin00Zbilinear30d26 1 QC2.45 [1.62, 3.09]2.42+0.57 [-0.73, 1.95]3.08 [2.20, 3.65]31% [15%, 57%]46%50%+0.32+0.332026-08-05 → 2026-08-30
tmin00Zbilinear90d26 1 QC2.45 [1.44, 3.15]2.42+0.57 [-0.82, 2.08]3.08 [1.97, 3.71]31% [14%, 62%]46%50%+0.32+0.332026-08-05 → 2026-08-30
tmin00Zbilinear365d26 1 QC2.45 [1.44, 3.14]2.42+0.57 [-0.85, 2.14]3.08 [1.98, 3.68]31% [14%, 64%]46%50%+0.32+0.332026-08-05 → 2026-08-30
tmin00Zbilinearall26 1 QC2.45 [1.27, 3.15]2.42+0.57 [-0.94, 2.36]3.08 [1.80, 3.66]31% [14%, 67%]46%50%+0.32+0.332026-08-05 → 2026-08-30
tmin00Znearest30d26 1 QC2.56 [1.75, 3.15]2.57+0.25 [-0.98, 1.54]3.14 [2.31, 3.70]19% [4%, 45%]38%58%+0.29+0.292026-08-05 → 2026-08-30
tmin00Znearest90d26 1 QC2.56 [1.46, 3.17]2.57+0.25 [-1.16, 1.64]3.14 [2.07, 3.68]19% [4%, 50%]38%58%+0.29+0.292026-08-05 → 2026-08-30
tmin00Znearest365d26 1 QC2.56 [1.47, 3.17]2.57+0.25 [-1.08, 1.72]3.14 [2.08, 3.69]19% [0%, 50%]38%58%+0.29+0.292026-08-05 → 2026-08-30
tmin00Znearestall26 1 QC2.56 [1.32, 3.17]2.57+0.25 [-1.22, 1.94]3.14 [1.96, 3.71]19% [0%, 60%]38%58%+0.29+0.292026-08-05 → 2026-08-30
tmin12Zbilinear30d26 1 QC2.55 [1.74, 3.48]2.47+0.98 [-0.46, 2.54]3.17 [2.11, 4.14]27% [16%, 40%]38%69%+0.29+0.322026-08-05 → 2026-08-30
tmin12Zbilinear90d26 1 QC2.55 [1.55, 3.54]2.47+0.98 [-0.63, 2.65]3.17 [1.90, 4.17]27% [14%, 43%]38%69%+0.29+0.322026-08-05 → 2026-08-30
tmin12Zbilinear365d26 1 QC2.55 [1.62, 3.58]2.47+0.98 [-0.61, 2.69]3.17 [1.96, 4.21]27% [14%, 42%]38%69%+0.29+0.322026-08-05 → 2026-08-30
tmin12Zbilinearall26 1 QC2.55 [1.54, 3.69]2.47+0.98 [-0.66, 3.01]3.17 [1.85, 4.26]27% [14%, 43%]38%69%+0.29+0.322026-08-05 → 2026-08-30
tmin12Znearest30d26 1 QC2.54 [1.84, 3.34]2.51+0.55 [-0.88, 2.07]3.08 [2.23, 3.88]23% [8%, 38%]42%65%+0.30+0.312026-08-05 → 2026-08-30
tmin12Znearest90d26 1 QC2.54 [1.65, 3.37]2.51+0.55 [-1.04, 2.24]3.08 [2.00, 3.93]23% [6%, 42%]42%65%+0.30+0.312026-08-05 → 2026-08-30
tmin12Znearest365d26 1 QC2.54 [1.75, 3.41]2.51+0.55 [-1.07, 2.23]3.08 [2.04, 3.95]23% [0%, 41%]42%65%+0.30+0.312026-08-05 → 2026-08-30
tmin12Znearestall26 1 QC2.54 [1.65, 3.52]2.51+0.55 [-1.13, 2.53]3.08 [1.98, 4.04]23% [3%, 41%]42%65%+0.30+0.312026-08-05 → 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 4, 00Z bilinear tmax+20+100-10-202026-08-05: +3.22 °F2026-08-06: -3.94 °F2026-08-07: -4.13 °F2026-08-08: +4.74 °F2026-08-09: +2.47 °F2026-08-10: -13.33 °F2026-08-11: -9.68 °F2026-08-12: +1.17 °F2026-08-13: -2.56 °F2026-08-14: -3.63 °F2026-08-15: +0.66 °F2026-08-16: -6.2 °F2026-08-17: -2.5 °F2026-08-18: +2.08 °F2026-08-19: -2.05 °F2026-08-20: -5.83 °F2026-08-21: +1.37 °F2026-08-22: +0.61 °F2026-08-23: +3.94 °F2026-08-24: +0.18 °F2026-08-25: +0.45 °F2026-08-26: +0.43 °F2026-08-27: -0.82 °F2026-08-28: +0.36 °F2026-08-29: -1.22 °F2026-08-30: +4.23 °F2026-08-052026-08-30°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 (26 days, newest first) · download CSV
Climatological dayError °F
2026-08-30+4.23
2026-08-29-1.22
2026-08-28+0.36
2026-08-27-0.82
2026-08-26+0.43
2026-08-25+0.45
2026-08-24+0.18
2026-08-23+3.94
2026-08-22+0.61
2026-08-21+1.37
2026-08-20-5.83
2026-08-19-2.05
2026-08-18+2.08
2026-08-17-2.50
2026-08-16-6.20
2026-08-15+0.66
2026-08-14-3.63
2026-08-13-2.56
2026-08-12+1.17
2026-08-11-9.68
2026-08-10-13.33
2026-08-09+2.47
2026-08-08+4.74
2026-08-07-4.13
2026-08-06-3.94
2026-08-05+3.22

Error distribution

Distribution of the signed daily error in °F for NCEP GFS at KORD, lead day 4-20 to -18 °F: 0 days-18 to -16 °F: 0 days-16 to -14 °F: 0 days-14 to -12 °F: 1 day-12 to -10 °F: 0 days-10 to -8 °F: 1 day-8 to -6 °F: 1 day-6 to -4 °F: 2 days-4 to -2 °F: 5 days-2 to 0 °F: 2 days0 to 2 °F: 8 days2 to 4 °F: 4 days4 to 6 °F: 2 days6 to 8 °F: 0 days8 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| 2.48 · P90 |e| 6.02 °F-200+20 °Fn = 26 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
-14.00-12.001
-12.00-10.000
-10.00-8.001
-8.00-6.001
-6.00-4.002
-4.00-2.005
-2.00+0.002
+0.00+2.008
+2.00+4.004
+4.00+6.002
+6.00+8.000
+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
2026-08263.15 -1.15

Availability

ModelScored period DaysCoverage
NCEP GFS2026-08-05 → 2026-08-30 26
NCEP GFS2026-08-05 → 2026-08-30 26
NCEP GFS2026-08-05 → 2026-08-30 26
NCEP GFS2026-08-05 → 2026-08-30 26

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 26 -0.04 [-1.92, 1.67] no
GraphCast (IFS init) 25 -0.98 [-2.88, 0.20] no
ECMWF IFS HRES 20 +0.12 [-1.64, 2.19] no
Persistence (baseline) 26 +0.07 [-1.25, 1.24] no

Cite this page

ShortCastCheck, KORD gfs lead 4, methodology v0.2, accessed 2026-08-31, https://castcheck.zifanzhang.com/station/KORD/model/gfs/lead/4/

LongCastCheck (2026). Station-level verification of raw weather-model 2 m temperature forecasts: KORD (Chicago O'Hare), model gfs, lead day 4. 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/4/

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