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

Trenton Mercer · NCEP GFS · lead day 6

KTTN · 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 QC3.70 [2.81, 4.52]3.50+1.18 [-0.16, 2.54]4.70 [3.63, 5.66]25% [12%, 38%]38%50%-0.01+0.042026-08-07 → 2026-08-30
tmax00Zbilinear90d24 1 QC3.70 [2.61, 4.50]3.50+1.18 [-0.11, 2.56]4.70 [3.37, 5.69]25% [11%, 40%]38%50%-0.01+0.042026-08-07 → 2026-08-30
tmax00Zbilinear365d24 1 QC3.70 [2.63, 4.54]3.50+1.18 [-0.16, 2.72]4.70 [3.37, 5.73]25% [9%, 39%]38%50%-0.01+0.042026-08-07 → 2026-08-30
tmax00Zbilinearall24 1 QC3.70 [2.63, 4.70]3.50+1.18 [-0.32, 2.68]4.70 [3.27, 5.89]25% [9%, 40%]38%50%-0.01+0.042026-08-07 → 2026-08-30
tmax00Znearest30d24 1 QC3.96 [2.96, 4.86]3.59+1.65 [0.26, 3.08]4.99 [3.83, 5.96]21% [9%, 32%]33%50%-0.08+0.012026-08-07 → 2026-08-30
tmax00Znearest90d24 1 QC3.96 [2.79, 4.88]3.59+1.65 [0.31, 3.12]4.99 [3.60, 5.99]21% [8%, 33%]33%50%-0.08+0.012026-08-07 → 2026-08-30
tmax00Znearest365d24 1 QC3.96 [2.75, 4.92]3.59+1.65 [0.25, 3.21]4.99 [3.60, 6.02]21% [5%, 33%]33%50%-0.08+0.012026-08-07 → 2026-08-30
tmax00Znearestall24 1 QC3.96 [2.67, 5.11]3.59+1.65 [0.09, 3.19]4.99 [3.34, 6.22]21% [7%, 32%]33%50%-0.08+0.012026-08-07 → 2026-08-30
tmax12Zbilinear30d24 1 QC4.09 [2.74, 5.42]4.09+0.32 [-2.03, 3.37]5.57 [3.64, 7.08]25% [10%, 40%]33%46%-0.12-0.122026-08-07 → 2026-08-30
tmax12Zbilinear90d24 1 QC4.09 [2.62, 5.67]4.09+0.32 [-2.42, 4.24]5.57 [3.47, 7.29]25% [8%, 41%]33%46%-0.12-0.122026-08-07 → 2026-08-30
tmax12Zbilinear365d24 1 QC4.09 [2.53, 5.77]4.09+0.32 [-2.71, 4.42]5.57 [3.29, 7.51]25% [6%, 43%]33%46%-0.12-0.122026-08-07 → 2026-08-30
tmax12Zbilinearall24 1 QC4.09 [2.50, 5.77]4.09+0.32 [-2.70, 4.65]5.57 [3.27, 7.61]25% [0%, 43%]33%46%-0.12-0.122026-08-07 → 2026-08-30
tmax12Znearest30d24 1 QC4.37 [2.91, 5.75]4.29+0.83 [-1.63, 4.02]5.81 [3.92, 7.25]25% [10%, 40%]29%42%-0.19-0.182026-08-07 → 2026-08-30
tmax12Znearest90d24 1 QC4.37 [2.81, 6.12]4.29+0.83 [-2.01, 5.04]5.81 [3.74, 7.47]25% [8%, 41%]29%42%-0.19-0.182026-08-07 → 2026-08-30
tmax12Znearest365d24 1 QC4.37 [2.80, 6.17]4.29+0.83 [-2.34, 5.20]5.81 [3.55, 7.69]25% [6%, 43%]29%42%-0.19-0.182026-08-07 → 2026-08-30
tmax12Znearestall24 1 QC4.37 [2.73, 6.05]4.29+0.83 [-2.37, 5.43]5.81 [3.48, 7.71]25% [0%, 43%]29%42%-0.19-0.182026-08-07 → 2026-08-30
tmin00Zbilinear30d24 1 QC4.60 [3.70, 5.61]2.78+3.44 [1.62, 5.33]5.23 [4.21, 6.37]4% [0%, 11%]8%25%-0.28+0.172026-08-07 → 2026-08-30
tmin00Zbilinear90d24 1 QC4.60 [3.72, 5.78]2.78+3.44 [1.71, 5.54]5.23 [4.16, 6.54]4% [0%, 12%]8%25%-0.28+0.172026-08-07 → 2026-08-30
tmin00Zbilinear365d24 1 QC4.60 [3.59, 5.77]2.78+3.44 [1.31, 5.57]5.23 [4.04, 6.54]4% [0%, 12%]8%25%-0.28+0.172026-08-07 → 2026-08-30
tmin00Zbilinearall24 1 QC4.60 [3.57, 5.95]2.78+3.44 [1.43, 5.76]5.23 [4.03, 6.76]4% [0%, 13%]8%25%-0.28+0.172026-08-07 → 2026-08-30
tmin00Znearest30d24 1 QC4.71 [3.77, 5.77]2.80+3.62 [1.76, 5.55]5.35 [4.25, 6.56]4% [0%, 11%]4%29%-0.32+0.162026-08-07 → 2026-08-30
tmin00Znearest90d24 1 QC4.71 [3.75, 5.91]2.80+3.62 [1.85, 5.73]5.35 [4.30, 6.72]4% [0%, 12%]4%29%-0.32+0.162026-08-07 → 2026-08-30
tmin00Znearest365d24 1 QC4.71 [3.62, 5.93]2.80+3.62 [1.48, 5.75]5.35 [4.12, 6.70]4% [0%, 12%]4%29%-0.32+0.162026-08-07 → 2026-08-30
tmin00Znearestall24 1 QC4.71 [3.60, 6.07]2.80+3.62 [1.61, 5.93]5.35 [4.11, 6.88]4% [0%, 13%]4%29%-0.32+0.162026-08-07 → 2026-08-30
tmin12Zbilinear30d24 1 QC4.74 [3.45, 6.54]3.71+3.24 [0.77, 6.30]5.82 [4.20, 7.67]12% [0%, 23%]17%33%-0.32-0.112026-08-07 → 2026-08-30
tmin12Zbilinear90d24 1 QC4.74 [3.41, 7.09]3.71+3.24 [0.73, 7.08]5.82 [4.24, 8.06]12% [0%, 24%]17%33%-0.32-0.112026-08-07 → 2026-08-30
tmin12Zbilinear365d24 1 QC4.74 [3.23, 7.05]3.71+3.24 [0.23, 7.05]5.82 [3.92, 8.00]12% [0%, 25%]17%33%-0.32-0.112026-08-07 → 2026-08-30
tmin12Zbilinearall24 1 QC4.74 [3.21, 7.31]3.71+3.24 [0.44, 7.31]5.82 [3.77, 8.33]12% [0%, 25%]17%33%-0.32-0.112026-08-07 → 2026-08-30
tmin12Znearest30d24 1 QC4.85 [3.42, 6.71]3.80+3.39 [0.83, 6.55]5.99 [4.31, 7.86]17% [0%, 30%]17%29%-0.35-0.132026-08-07 → 2026-08-30
tmin12Znearest90d24 1 QC4.85 [3.39, 7.34]3.80+3.39 [0.80, 7.28]5.99 [4.32, 8.26]17% [0%, 31%]17%29%-0.35-0.132026-08-07 → 2026-08-30
tmin12Znearest365d24 1 QC4.85 [3.22, 7.26]3.80+3.39 [0.34, 7.19]5.99 [3.94, 8.22]17% [0%, 32%]17%29%-0.35-0.132026-08-07 → 2026-08-30
tmin12Znearestall24 1 QC4.85 [3.24, 7.49]3.80+3.39 [0.51, 7.49]5.99 [3.86, 8.52]17% [0%, 31%]17%29%-0.35-0.132026-08-07 → 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 KTTN, lead day 6, 00Z bilinear tmax+10+50-5-102026-08-07: -0.68 °F2026-08-08: +3.85 °F2026-08-09: +3.11 °F2026-08-10: +5.77 °F2026-08-11: +6.6 °F2026-08-12: -3.49 °F2026-08-13: -1.83 °F2026-08-14: +1.58 °F2026-08-15: -7.41 °F2026-08-16: +2.51 °F2026-08-17: -0.83 °F2026-08-18: -0.74 °F2026-08-19: +2 °F2026-08-20: +7.58 °F2026-08-21: +2.04 °F2026-08-22: -9.27 °F2026-08-23: +6.64 °F2026-08-24: +0.42 °F2026-08-25: +9.69 °F2026-08-26: -0.01 °F2026-08-27: -5.99 °F2026-08-28: +0.8 °F2026-08-29: +1.35 °F2026-08-30: +4.57 °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+4.57
2026-08-29+1.35
2026-08-28+0.80
2026-08-27-5.99
2026-08-26-0.01
2026-08-25+9.69
2026-08-24+0.42
2026-08-23+6.64
2026-08-22-9.27
2026-08-21+2.04
2026-08-20+7.58
2026-08-19+2.00
2026-08-18-0.74
2026-08-17-0.83
2026-08-16+2.51
2026-08-15-7.41
2026-08-14+1.58
2026-08-13-1.83
2026-08-12-3.49
2026-08-11+6.60
2026-08-10+5.77
2026-08-09+3.11
2026-08-08+3.85
2026-08-07-0.68

Error distribution

Distribution of the signed daily error in °F for NCEP GFS at KTTN, lead day 6-10 to -9 °F: 1 day-9 to -8 °F: 0 days-8 to -7 °F: 1 day-7 to -6 °F: 0 days-6 to -5 °F: 1 day-5 to -4 °F: 0 days-4 to -3 °F: 1 day-3 to -2 °F: 0 days-2 to -1 °F: 1 day-1 to 0 °F: 4 days0 to 1 °F: 2 days1 to 2 °F: 2 days2 to 3 °F: 3 days3 to 4 °F: 2 days4 to 5 °F: 1 day5 to 6 °F: 1 day6 to 7 °F: 2 days7 to 8 °F: 1 day8 to 9 °F: 0 days9 to 10 °F: 1 daydashed: P50 |e| 2.81 · P90 |e| 7.53 °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
-10.00-9.001
-9.00-8.000
-8.00-7.001
-7.00-6.000
-6.00-5.001
-5.00-4.000
-4.00-3.001
-3.00-2.000
-2.00-1.001
-1.00+0.004
+0.00+1.002
+1.00+2.002
+2.00+3.003
+3.00+4.002
+4.00+5.001
+5.00+6.001
+6.00+7.002
+7.00+8.001
+8.00+9.000
+9.00+10.001

Month by month

00Z bilinear daily maximum, newest first.

Monthn MAE °FBias °F
2026-08243.70 +1.18

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 +1.78 [0.73, 2.53] yes
GraphCast (IFS init) 24 +1.45 [0.15, 2.40] yes
ECMWF IFS HRES 19 -0.71 [-3.89, 1.59] no
Persistence (baseline) 24 +0.03 [-1.35, 1.19] no

Cite this page

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

LongCastCheck (2026). Station-level verification of raw weather-model 2 m temperature forecasts: KTTN (Trenton Mercer), 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/KTTN/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