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 2

KORD · gfs · lead 2

Target day = initialization date + 2 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
tmax00Zbilinear30d28 1 QC2.94 [2.45, 3.45]2.62-1.21 [-2.20, -0.33]3.49 [2.96, 4.01]18% [7%, 29%]39%61%+0.09+0.202026-08-03 → 2026-08-30
tmax00Zbilinear90d28 1 QC2.94 [2.42, 3.51]2.62-1.21 [-2.39, -0.19]3.49 [2.90, 4.08]18% [6%, 30%]39%61%+0.09+0.202026-08-03 → 2026-08-30
tmax00Zbilinear365d28 1 QC2.94 [2.38, 3.55]2.62-1.21 [-2.32, -0.15]3.49 [2.88, 4.08]18% [5%, 30%]39%61%+0.09+0.202026-08-03 → 2026-08-30
tmax00Zbilinearall28 1 QC2.94 [2.43, 3.59]2.62-1.21 [-2.39, -0.23]3.49 [2.90, 4.14]18% [6%, 29%]39%61%+0.09+0.202026-08-03 → 2026-08-30
tmax00Znearest30d28 1 QC2.97 [2.40, 3.58]2.53-1.47 [-2.50, -0.41]3.62 [2.95, 4.26]14% [4%, 27%]39%68%+0.08+0.232026-08-03 → 2026-08-30
tmax00Znearest90d28 1 QC2.97 [2.33, 3.63]2.53-1.47 [-2.64, -0.40]3.62 [2.86, 4.35]14% [0%, 27%]39%68%+0.08+0.232026-08-03 → 2026-08-30
tmax00Znearest365d28 1 QC2.97 [2.32, 3.66]2.53-1.47 [-2.62, -0.39]3.62 [2.80, 4.33]14% [0%, 29%]39%68%+0.08+0.232026-08-03 → 2026-08-30
tmax00Znearestall28 1 QC2.97 [2.35, 3.68]2.53-1.47 [-2.61, -0.46]3.62 [2.84, 4.35]14% [0%, 29%]39%68%+0.08+0.232026-08-03 → 2026-08-30
tmax12Zbilinear30d28 1 QC2.22 [1.54, 3.13]2.20-0.27 [-1.01, 0.45]3.19 [2.06, 4.34]39% [18%, 60%]64%82%+0.31+0.332026-08-03 → 2026-08-30
tmax12Zbilinear90d28 1 QC2.22 [1.47, 3.21]2.20-0.27 [-1.02, 0.66]3.19 [1.93, 4.33]39% [17%, 61%]64%82%+0.31+0.332026-08-03 → 2026-08-30
tmax12Zbilinear365d28 1 QC2.22 [1.50, 3.33]2.20-0.27 [-1.01, 0.61]3.19 [1.94, 4.51]39% [13%, 62%]64%82%+0.31+0.332026-08-03 → 2026-08-30
tmax12Zbilinearall28 1 QC2.22 [1.49, 3.32]2.20-0.27 [-1.10, 0.60]3.19 [1.91, 4.40]39% [14%, 62%]64%82%+0.31+0.332026-08-03 → 2026-08-30
tmax12Znearest30d28 1 QC2.14 [1.40, 3.04]2.05-0.41 [-1.32, 0.39]3.19 [1.84, 4.37]39% [23%, 58%]68%86%+0.34+0.372026-08-03 → 2026-08-30
tmax12Znearest90d28 1 QC2.14 [1.25, 3.06]2.05-0.41 [-1.27, 0.55]3.19 [1.59, 4.37]39% [24%, 63%]68%86%+0.34+0.372026-08-03 → 2026-08-30
tmax12Znearest365d28 1 QC2.14 [1.27, 3.16]2.05-0.41 [-1.28, 0.51]3.19 [1.65, 4.47]39% [24%, 62%]68%86%+0.34+0.372026-08-03 → 2026-08-30
tmax12Znearestall28 1 QC2.14 [1.20, 3.18]2.05-0.41 [-1.31, 0.52]3.19 [1.53, 4.42]39% [23%, 64%]68%86%+0.34+0.372026-08-03 → 2026-08-30
tmin00Zbilinear30d28 1 QC1.88 [1.49, 2.44]1.85+0.46 [-0.21, 1.26]2.35 [1.85, 2.90]32% [17%, 48%]61%82%+0.40+0.422026-08-03 → 2026-08-30
tmin00Zbilinear90d28 1 QC1.88 [1.33, 2.46]1.85+0.46 [-0.20, 1.35]2.35 [1.74, 2.97]32% [14%, 50%]61%82%+0.40+0.422026-08-03 → 2026-08-30
tmin00Zbilinear365d28 1 QC1.88 [1.27, 2.50]1.85+0.46 [-0.26, 1.39]2.35 [1.65, 2.97]32% [14%, 50%]61%82%+0.40+0.422026-08-03 → 2026-08-30
tmin00Zbilinearall28 1 QC1.88 [1.30, 2.56]1.85+0.46 [-0.26, 1.48]2.35 [1.72, 3.03]32% [12%, 52%]61%82%+0.40+0.422026-08-03 → 2026-08-30
tmin00Znearest30d28 1 QC1.85 [1.52, 2.26]1.85-0.00 [-0.62, 0.74]2.23 [1.81, 2.72]32% [17%, 54%]61%86%+0.41+0.422026-08-03 → 2026-08-30
tmin00Znearest90d28 1 QC1.85 [1.37, 2.31]1.85-0.00 [-0.60, 0.83]2.23 [1.73, 2.73]32% [14%, 61%]61%86%+0.41+0.422026-08-03 → 2026-08-30
tmin00Znearest365d28 1 QC1.85 [1.30, 2.32]1.85-0.00 [-0.65, 0.81]2.23 [1.64, 2.75]32% [14%, 68%]61%86%+0.41+0.422026-08-03 → 2026-08-30
tmin00Znearestall28 1 QC1.85 [1.38, 2.35]1.85-0.00 [-0.69, 0.90]2.23 [1.70, 2.79]32% [14%, 62%]61%86%+0.41+0.422026-08-03 → 2026-08-30
tmin12Zbilinear30d28 1 QC2.20 [1.92, 2.49]2.05+0.42 [-0.36, 1.29]2.53 [2.28, 2.82]21% [7%, 35%]46%75%+0.30+0.362026-08-03 → 2026-08-30
tmin12Zbilinear90d28 1 QC2.20 [1.75, 2.54]2.05+0.42 [-0.39, 1.39]2.53 [2.14, 2.91]21% [8%, 38%]46%75%+0.30+0.362026-08-03 → 2026-08-30
tmin12Zbilinear365d28 1 QC2.20 [1.74, 2.57]2.05+0.42 [-0.34, 1.41]2.53 [2.11, 2.89]21% [7%, 38%]46%75%+0.30+0.362026-08-03 → 2026-08-30
tmin12Zbilinearall28 1 QC2.20 [1.81, 2.60]2.05+0.42 [-0.36, 1.46]2.53 [2.19, 2.90]21% [8%, 36%]46%75%+0.30+0.362026-08-03 → 2026-08-30
tmin12Znearest30d28 1 QC2.10 [1.71, 2.47]2.10-0.04 [-0.80, 0.85]2.58 [2.21, 2.93]29% [13%, 50%]50%79%+0.33+0.342026-08-03 → 2026-08-30
tmin12Znearest90d28 1 QC2.10 [1.49, 2.54]2.10-0.04 [-0.80, 0.92]2.58 [2.10, 2.97]29% [13%, 57%]50%79%+0.33+0.342026-08-03 → 2026-08-30
tmin12Znearest365d28 1 QC2.10 [1.47, 2.56]2.10-0.04 [-0.77, 0.96]2.58 [2.04, 2.96]29% [12%, 60%]50%79%+0.33+0.342026-08-03 → 2026-08-30
tmin12Znearestall28 1 QC2.10 [1.53, 2.57]2.10-0.04 [-0.79, 0.98]2.58 [2.13, 2.98]29% [12%, 56%]50%79%+0.33+0.342026-08-03 → 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 2, 00Z bilinear tmax+10+50-5-102026-08-03: -5.5 °F2026-08-04: -2.13 °F2026-08-05: +0.41 °F2026-08-06: -6.48 °F2026-08-07: -1.9 °F2026-08-08: +2.51 °F2026-08-09: -6.5 °F2026-08-10: -2.32 °F2026-08-11: -0.83 °F2026-08-12: -5.6 °F2026-08-13: +5.51 °F2026-08-14: -3.2 °F2026-08-15: +2.78 °F2026-08-16: -1.41 °F2026-08-17: -1.88 °F2026-08-18: +1.61 °F2026-08-19: -3.22 °F2026-08-20: +5.67 °F2026-08-21: -2.68 °F2026-08-22: -1.37 °F2026-08-23: +0.75 °F2026-08-24: +0.95 °F2026-08-25: -1.73 °F2026-08-26: -5.3 °F2026-08-27: -2.64 °F2026-08-28: +0.07 °F2026-08-29: -3.35 °F2026-08-30: +3.91 °F2026-08-032026-08-30°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 (28 days, newest first) · download CSV
Climatological dayError °F
2026-08-30+3.91
2026-08-29-3.35
2026-08-28+0.07
2026-08-27-2.64
2026-08-26-5.30
2026-08-25-1.73
2026-08-24+0.95
2026-08-23+0.75
2026-08-22-1.37
2026-08-21-2.68
2026-08-20+5.67
2026-08-19-3.22
2026-08-18+1.61
2026-08-17-1.88
2026-08-16-1.41
2026-08-15+2.78
2026-08-14-3.20
2026-08-13+5.51
2026-08-12-5.60
2026-08-11-0.83
2026-08-10-2.32
2026-08-09-6.50
2026-08-08+2.51
2026-08-07-1.90
2026-08-06-6.48
2026-08-05+0.41
2026-08-04-2.13
2026-08-03-5.50

Error distribution

Distribution of the signed daily error in °F for NCEP GFS at KORD, lead day 2-10 to -9 °F: 0 days-9 to -8 °F: 0 days-8 to -7 °F: 0 days-7 to -6 °F: 2 days-6 to -5 °F: 3 days-5 to -4 °F: 0 days-4 to -3 °F: 3 days-3 to -2 °F: 4 days-2 to -1 °F: 5 days-1 to 0 °F: 1 day0 to 1 °F: 4 days1 to 2 °F: 1 day2 to 3 °F: 2 days3 to 4 °F: 1 day4 to 5 °F: 0 days5 to 6 °F: 2 days6 to 7 °F: 0 days7 to 8 °F: 0 days8 to 9 °F: 0 days9 to 10 °F: 0 daysdashed: P50 |e| 2.57 · P90 |e| 5.62 °F-100+10 °Fn = 28 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
-8.00-7.000
-7.00-6.002
-6.00-5.003
-5.00-4.000
-4.00-3.003
-3.00-2.004
-2.00-1.005
-1.00+0.001
+0.00+1.004
+1.00+2.001
+2.00+3.002
+3.00+4.001
+4.00+5.000
+5.00+6.002
+6.00+7.000
+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
2026-08282.94 -1.21

Availability

ModelScored period DaysCoverage
NCEP GFS2026-08-03 → 2026-08-30 28
NCEP GFS2026-08-03 → 2026-08-30 28
NCEP GFS2026-08-03 → 2026-08-30 28
NCEP GFS2026-08-03 → 2026-08-30 28

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 28 -0.64 [-1.64, 0.31] no
Aurora (IFS init) 1 +2.48 [2.48, 2.48] yes
FourCastNet v2 (IFS init) 1 +3.89 [3.89, 3.89] yes
GraphCast (IFS init) 26 -1.26 [-2.59, -0.11] yes
ECMWF IFS HRES 22 +0.11 [-0.75, 0.89] no
Pangu-Weather (IFS init) 1 +2.47 [2.47, 2.47] yes
Persistence (baseline) 28 -0.28 [-1.43, 0.66] no

Cite this page

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

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

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