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 8

KORD · gfs · lead 8

Target day = initialization date + 8 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
tmax00Zbilinear30d22 1 QC4.65 [3.14, 5.82]4.65-2.17 [-4.31, 0.33]5.93 [3.98, 7.38]9% [0%, 18%]27%41%-0.23-0.232026-08-09 → 2026-08-30
tmax00Zbilinear90d22 1 QC4.65 [2.99, 5.86]4.65-2.17 [-4.30, 0.45]5.93 [3.47, 7.41]9% [0%, 18%]27%41%-0.23-0.232026-08-09 → 2026-08-30
tmax00Zbilinear365d22 1 QC4.65 [2.80, 5.81]4.65-2.17 [-4.36, 0.80]5.93 [3.41, 7.50]9% [0%, 18%]27%41%-0.23-0.232026-08-09 → 2026-08-30
tmax00Zbilinearall22 1 QC4.65 [2.92, 5.89]4.65-2.17 [-4.37, 0.69]5.93 [3.15, 7.41]9% [0%, 18%]27%41%-0.23-0.232026-08-09 → 2026-08-30
tmax00Znearest30d22 1 QC4.68 [3.29, 5.69]4.75-2.07 [-4.25, 0.46]5.91 [4.00, 7.44]9% [0%, 21%]27%36%-0.24-0.262026-08-09 → 2026-08-30
tmax00Znearest90d22 1 QC4.68 [3.08, 5.68]4.75-2.07 [-4.35, 0.67]5.91 [3.54, 7.48]9% [0%, 25%]27%36%-0.24-0.262026-08-09 → 2026-08-30
tmax00Znearest365d22 1 QC4.68 [3.11, 5.71]4.75-2.07 [-4.40, 0.97]5.91 [3.65, 7.55]9% [0%, 25%]27%36%-0.24-0.262026-08-09 → 2026-08-30
tmax00Znearestall22 1 QC4.68 [3.00, 5.70]4.75-2.07 [-4.36, 0.68]5.91 [3.54, 7.45]9% [0%, 30%]27%36%-0.24-0.262026-08-09 → 2026-08-30
tmax12Zbilinear30d22 1 QC4.45 [2.99, 5.34]4.29-1.22 [-2.85, 0.66]5.34 [4.04, 6.10]18% [6%, 36%]27%36%-0.18-0.142026-08-09 → 2026-08-30
tmax12Zbilinear90d22 1 QC4.45 [2.58, 5.36]4.29-1.22 [-2.87, 0.76]5.34 [3.36, 6.11]18% [5%, 38%]27%36%-0.18-0.142026-08-09 → 2026-08-30
tmax12Zbilinear365d22 1 QC4.45 [2.58, 5.37]4.29-1.22 [-2.87, 0.98]5.34 [3.36, 6.16]18% [6%, 38%]27%36%-0.18-0.142026-08-09 → 2026-08-30
tmax12Zbilinearall22 1 QC4.45 [2.46, 5.58]4.29-1.22 [-3.01, 1.34]5.34 [3.18, 6.24]18% [0%, 40%]27%36%-0.18-0.142026-08-09 → 2026-08-30
tmax12Znearest30d22 1 QC4.17 [2.82, 5.19]4.06-1.23 [-2.88, 0.65]5.07 [3.75, 6.00]18% [6%, 37%]32%41%-0.11-0.082026-08-09 → 2026-08-30
tmax12Znearest90d22 1 QC4.17 [2.36, 5.24]4.06-1.23 [-2.91, 0.75]5.07 [3.12, 5.95]18% [5%, 38%]32%41%-0.11-0.082026-08-09 → 2026-08-30
tmax12Znearest365d22 1 QC4.17 [2.36, 5.21]4.06-1.23 [-2.95, 1.00]5.07 [3.03, 6.02]18% [6%, 38%]32%41%-0.11-0.082026-08-09 → 2026-08-30
tmax12Znearestall22 1 QC4.17 [2.24, 5.37]4.06-1.23 [-3.12, 1.21]5.07 [2.68, 6.11]18% [0%, 40%]32%41%-0.11-0.082026-08-09 → 2026-08-30
tmin00Zbilinear30d22 1 QC5.17 [3.83, 6.48]5.16-0.17 [-3.28, 3.22]6.15 [4.66, 7.25]14% [0%, 25%]27%32%-0.14-0.092026-08-09 → 2026-08-30
tmin00Zbilinear90d22 1 QC5.17 [3.69, 6.50]5.16-0.17 [-3.39, 3.74]6.15 [4.48, 7.34]14% [0%, 27%]27%32%-0.14-0.092026-08-09 → 2026-08-30
tmin00Zbilinear365d22 1 QC5.17 [3.66, 6.72]5.16-0.17 [-3.32, 3.76]6.15 [4.41, 7.44]14% [0%, 29%]27%32%-0.14-0.092026-08-09 → 2026-08-30
tmin00Zbilinearall22 1 QC5.17 [3.67, 6.94]5.16-0.17 [-3.84, 4.00]6.15 [4.40, 7.54]14% [0%, 29%]27%32%-0.14-0.092026-08-09 → 2026-08-30
tmin00Znearest30d22 1 QC5.35 [4.06, 6.55]5.27-0.66 [-3.76, 2.76]6.32 [4.98, 7.37]14% [0%, 25%]23%32%-0.18-0.112026-08-09 → 2026-08-30
tmin00Znearest90d22 1 QC5.35 [3.89, 6.53]5.27-0.66 [-3.93, 3.31]6.32 [4.74, 7.40]14% [0%, 27%]23%32%-0.18-0.112026-08-09 → 2026-08-30
tmin00Znearest365d22 1 QC5.35 [3.95, 6.81]5.27-0.66 [-3.87, 3.35]6.32 [4.65, 7.46]14% [0%, 29%]23%32%-0.18-0.112026-08-09 → 2026-08-30
tmin00Znearestall22 1 QC5.35 [3.82, 6.88]5.27-0.66 [-4.31, 3.50]6.32 [4.61, 7.55]14% [0%, 29%]23%32%-0.18-0.112026-08-09 → 2026-08-30
tmin12Zbilinear30d22 1 QC4.58 [2.58, 6.47]4.74+0.62 [-2.95, 4.22]6.26 [3.28, 8.27]27% [12%, 40%]32%41%-0.01+0.002026-08-09 → 2026-08-30
tmin12Zbilinear90d22 1 QC4.58 [2.21, 6.66]4.74+0.62 [-3.05, 4.40]6.26 [2.67, 8.43]27% [9%, 40%]32%41%-0.01+0.002026-08-09 → 2026-08-30
tmin12Zbilinear365d22 1 QC4.58 [2.23, 6.88]4.74+0.62 [-3.23, 4.88]6.26 [2.73, 8.77]27% [5%, 40%]32%41%-0.01+0.002026-08-09 → 2026-08-30
tmin12Zbilinearall22 1 QC4.58 [2.27, 6.87]4.74+0.62 [-3.39, 5.01]6.26 [2.71, 8.60]27% [0%, 40%]32%41%-0.01+0.002026-08-09 → 2026-08-30
tmin12Znearest30d22 1 QC4.76 [2.85, 6.45]4.80+0.18 [-3.33, 3.73]6.24 [3.40, 8.08]18% [5%, 31%]32%36%-0.05-0.012026-08-09 → 2026-08-30
tmin12Znearest90d22 1 QC4.76 [2.44, 6.69]4.80+0.18 [-3.49, 3.92]6.24 [2.85, 8.22]18% [0%, 33%]32%36%-0.05-0.012026-08-09 → 2026-08-30
tmin12Znearest365d22 1 QC4.76 [2.47, 6.83]4.80+0.18 [-3.63, 4.41]6.24 [2.92, 8.53]18% [0%, 33%]32%36%-0.05-0.012026-08-09 → 2026-08-30
tmin12Znearestall22 1 QC4.76 [2.51, 6.76]4.80+0.18 [-3.78, 4.50]6.24 [2.90, 8.32]18% [0%, 33%]32%36%-0.05-0.012026-08-09 → 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 8, 00Z bilinear tmax+20+100-10-202026-08-09: -3.02 °F2026-08-10: +2.97 °F2026-08-11: -4.78 °F2026-08-12: -9.83 °F2026-08-13: -6.04 °F2026-08-14: -7.86 °F2026-08-15: +1.03 °F2026-08-16: -8.22 °F2026-08-17: +1.83 °F2026-08-18: +0.2 °F2026-08-19: +2.11 °F2026-08-20: -3.45 °F2026-08-21: +4.46 °F2026-08-22: -3.91 °F2026-08-23: +6.4 °F2026-08-24: +5.73 °F2026-08-25: +1.4 °F2026-08-26: -14.51 °F2026-08-27: -10.98 °F2026-08-28: -0.01 °F2026-08-29: -2.48 °F2026-08-30: +1.12 °F2026-08-092026-08-30°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 (22 days, newest first) · download CSV
Climatological dayError °F
2026-08-30+1.12
2026-08-29-2.48
2026-08-28-0.01
2026-08-27-10.98
2026-08-26-14.51
2026-08-25+1.40
2026-08-24+5.73
2026-08-23+6.40
2026-08-22-3.91
2026-08-21+4.46
2026-08-20-3.45
2026-08-19+2.11
2026-08-18+0.20
2026-08-17+1.83
2026-08-16-8.22
2026-08-15+1.03
2026-08-14-7.86
2026-08-13-6.04
2026-08-12-9.83
2026-08-11-4.78
2026-08-10+2.97
2026-08-09-3.02

Error distribution

Distribution of the signed daily error in °F for NCEP GFS at KORD, lead day 8-20 to -18 °F: 0 days-18 to -16 °F: 0 days-16 to -14 °F: 1 day-14 to -12 °F: 0 days-12 to -10 °F: 1 day-10 to -8 °F: 2 days-8 to -6 °F: 2 days-6 to -4 °F: 1 day-4 to -2 °F: 4 days-2 to 0 °F: 1 day0 to 2 °F: 5 days2 to 4 °F: 2 days4 to 6 °F: 2 days6 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| 3.68 · P90 |e| 9.67 °F-200+20 °Fn = 22 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
-16.00-14.001
-14.00-12.000
-12.00-10.001
-10.00-8.002
-8.00-6.002
-6.00-4.001
-4.00-2.004
-2.00+0.001
+0.00+2.005
+2.00+4.002
+4.00+6.002
+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
2026-08224.65 -2.17

Availability

ModelScored period DaysCoverage
NCEP GFS2026-08-09 → 2026-08-30 22
NCEP GFS2026-08-09 → 2026-08-30 22
NCEP GFS2026-08-09 → 2026-08-30 22
NCEP GFS2026-08-09 → 2026-08-30 22

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 22 -0.88 [-3.12, 0.97] no
GraphCast (IFS init) 22 +0.09 [-2.51, 1.60] no
ECMWF IFS HRES 17 -0.96 [-2.95, 1.50] no
Persistence (baseline) 22 +0.88 [-1.66, 2.69] no

Cite this page

ShortCastCheck, KORD gfs lead 8, methodology v0.2, accessed 2026-08-31, https://castcheck.zifanzhang.com/station/KORD/model/gfs/lead/8/

LongCastCheck (2026). Station-level verification of raw weather-model 2 m temperature forecasts: KORD (Chicago O'Hare), model gfs, lead day 8. 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/8/

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