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 4

KTTN · 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 [2.37, 4.05]3.06+1.01 [-0.42, 2.79]3.88 [2.91, 4.81]23% [11%, 36%]38%50%+0.11+0.122026-08-05 → 2026-08-30
tmax00Zbilinear90d26 1 QC3.15 [2.27, 4.10]3.06+1.01 [-0.54, 3.11]3.88 [2.77, 4.83]23% [10%, 36%]38%50%+0.11+0.122026-08-05 → 2026-08-30
tmax00Zbilinear365d26 1 QC3.15 [2.22, 4.15]3.06+1.01 [-0.67, 3.48]3.88 [2.73, 4.92]23% [9%, 36%]38%50%+0.11+0.122026-08-05 → 2026-08-30
tmax00Zbilinearall26 1 QC3.15 [2.20, 4.19]3.06+1.01 [-0.67, 3.18]3.88 [2.70, 4.84]23% [10%, 38%]38%50%+0.11+0.122026-08-05 → 2026-08-30
tmax00Znearest30d26 1 QC3.35 [2.54, 4.42]3.14+1.58 [0.09, 3.39]4.19 [3.17, 5.20]23% [10%, 35%]38%46%+0.05+0.102026-08-05 → 2026-08-30
tmax00Znearest90d26 1 QC3.35 [2.44, 4.41]3.14+1.58 [-0.09, 3.80]4.19 [3.04, 5.26]23% [7%, 34%]38%46%+0.05+0.102026-08-05 → 2026-08-30
tmax00Znearest365d26 1 QC3.35 [2.33, 4.61]3.14+1.58 [-0.19, 4.13]4.19 [2.97, 5.42]23% [5%, 36%]38%46%+0.05+0.102026-08-05 → 2026-08-30
tmax00Znearestall26 1 QC3.35 [2.39, 4.56]3.14+1.58 [-0.14, 3.79]4.19 [3.02, 5.32]23% [5%, 36%]38%46%+0.05+0.102026-08-05 → 2026-08-30
tmax12Zbilinear30d26 1 QC3.79 [2.45, 5.27]3.80-0.34 [-2.75, 1.94]4.93 [2.95, 6.56]15% [3%, 30%]23%54%-0.07-0.092026-08-05 → 2026-08-30
tmax12Zbilinear90d26 1 QC3.79 [2.38, 5.46]3.80-0.34 [-3.07, 2.38]4.93 [2.84, 6.71]15% [0%, 35%]23%54%-0.07-0.092026-08-05 → 2026-08-30
tmax12Zbilinear365d26 1 QC3.79 [2.28, 5.61]3.80-0.34 [-3.34, 2.41]4.93 [2.77, 6.79]15% [0%, 33%]23%54%-0.07-0.092026-08-05 → 2026-08-30
tmax12Zbilinearall26 1 QC3.79 [2.31, 5.66]3.80-0.34 [-3.14, 2.35]4.93 [2.74, 6.95]15% [0%, 35%]23%54%-0.07-0.092026-08-05 → 2026-08-30
tmax12Znearest30d26 1 QC4.00 [2.67, 5.43]3.97+0.23 [-2.31, 2.64]5.10 [3.24, 6.61]15% [3%, 29%]31%46%-0.13-0.142026-08-05 → 2026-08-30
tmax12Znearest90d26 1 QC4.00 [2.60, 5.57]3.97+0.23 [-2.65, 3.08]5.10 [3.08, 6.74]15% [0%, 29%]31%46%-0.13-0.142026-08-05 → 2026-08-30
tmax12Znearest365d26 1 QC4.00 [2.49, 5.73]3.97+0.23 [-2.96, 3.08]5.10 [3.02, 6.88]15% [0%, 33%]31%46%-0.13-0.142026-08-05 → 2026-08-30
tmax12Znearestall26 1 QC4.00 [2.49, 5.88]3.97+0.23 [-2.90, 3.05]5.10 [2.90, 6.98]15% [0%, 31%]31%46%-0.13-0.142026-08-05 → 2026-08-30
tmin00Zbilinear30d26 1 QC4.05 [3.35, 4.67]2.53+3.49 [2.16, 4.49]4.69 [4.11, 5.21]15% [3%, 30%]27%35%-0.24+0.232026-08-05 → 2026-08-30
tmin00Zbilinear90d26 1 QC4.05 [3.35, 4.71]2.53+3.49 [2.22, 4.54]4.69 [4.08, 5.24]15% [0%, 31%]27%35%-0.24+0.232026-08-05 → 2026-08-30
tmin00Zbilinear365d26 1 QC4.05 [3.32, 4.77]2.53+3.49 [2.08, 4.58]4.69 [4.03, 5.28]15% [0%, 32%]27%35%-0.24+0.232026-08-05 → 2026-08-30
tmin00Zbilinearall26 1 QC4.05 [3.33, 4.87]2.53+3.49 [2.09, 4.61]4.69 [4.06, 5.36]15% [0%, 31%]27%35%-0.24+0.232026-08-05 → 2026-08-30
tmin00Znearest30d26 1 QC4.26 [3.50, 4.92]2.66+3.66 [2.28, 4.73]4.92 [4.25, 5.49]15% [3%, 30%]27%31%-0.30+0.192026-08-05 → 2026-08-30
tmin00Znearest90d26 1 QC4.26 [3.49, 4.97]2.66+3.66 [2.31, 4.78]4.92 [4.21, 5.53]15% [0%, 31%]27%31%-0.30+0.192026-08-05 → 2026-08-30
tmin00Znearest365d26 1 QC4.26 [3.44, 5.01]2.66+3.66 [2.14, 4.83]4.92 [4.20, 5.57]15% [0%, 32%]27%31%-0.30+0.192026-08-05 → 2026-08-30
tmin00Znearestall26 1 QC4.26 [3.43, 5.16]2.66+3.66 [2.18, 4.86]4.92 [4.16, 5.65]15% [0%, 31%]27%31%-0.30+0.192026-08-05 → 2026-08-30
tmin12Zbilinear30d26 1 QC3.64 [2.97, 4.47]2.72+3.19 [2.03, 4.36]4.55 [3.77, 5.42]23% [7%, 43%]31%42%-0.11+0.172026-08-05 → 2026-08-30
tmin12Zbilinear90d26 1 QC3.64 [2.80, 4.73]2.72+3.19 [1.96, 4.60]4.55 [3.71, 5.67]23% [6%, 48%]31%42%-0.11+0.172026-08-05 → 2026-08-30
tmin12Zbilinear365d26 1 QC3.64 [2.71, 4.84]2.72+3.19 [1.77, 4.80]4.55 [3.61, 5.76]23% [0%, 45%]31%42%-0.11+0.172026-08-05 → 2026-08-30
tmin12Zbilinearall26 1 QC3.64 [2.70, 4.81]2.72+3.19 [1.79, 4.73]4.55 [3.59, 5.88]23% [5%, 48%]31%42%-0.11+0.172026-08-05 → 2026-08-30
tmin12Znearest30d26 1 QC3.80 [3.03, 4.68]2.87+3.34 [2.09, 4.57]4.77 [3.91, 5.63]27% [11%, 44%]31%42%-0.16+0.122026-08-05 → 2026-08-30
tmin12Znearest90d26 1 QC3.80 [2.89, 4.97]2.87+3.34 [2.05, 4.80]4.77 [3.86, 5.92]27% [10%, 50%]31%42%-0.16+0.122026-08-05 → 2026-08-30
tmin12Znearest365d26 1 QC3.80 [2.78, 5.06]2.87+3.34 [1.83, 5.03]4.77 [3.73, 5.96]27% [0%, 50%]31%42%-0.16+0.122026-08-05 → 2026-08-30
tmin12Znearestall26 1 QC3.80 [2.76, 5.00]2.87+3.34 [1.87, 4.94]4.77 [3.70, 6.05]27% [8%, 50%]31%42%-0.16+0.122026-08-05 → 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 KTTN, lead day 4, 00Z bilinear tmax+10+50-5-102026-08-05: -3.63 °F2026-08-06: -0.41 °F2026-08-07: +2.03 °F2026-08-08: +0.09 °F2026-08-09: +3.38 °F2026-08-10: +4.77 °F2026-08-11: +3.15 °F2026-08-12: +0.35 °F2026-08-13: -1.38 °F2026-08-14: -4.61 °F2026-08-15: -6.34 °F2026-08-16: +6.1 °F2026-08-17: -1.73 °F2026-08-18: +1.92 °F2026-08-19: +3.39 °F2026-08-20: -5.24 °F2026-08-21: -1.48 °F2026-08-22: +0.93 °F2026-08-23: -0.8 °F2026-08-24: -2.15 °F2026-08-25: +4.82 °F2026-08-26: +2.38 °F2026-08-27: +9.31 °F2026-08-28: +6.12 °F2026-08-29: +0.87 °F2026-08-30: +4.55 °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+4.55
2026-08-29+0.87
2026-08-28+6.12
2026-08-27+9.31
2026-08-26+2.38
2026-08-25+4.82
2026-08-24-2.15
2026-08-23-0.80
2026-08-22+0.93
2026-08-21-1.48
2026-08-20-5.24
2026-08-19+3.39
2026-08-18+1.92
2026-08-17-1.73
2026-08-16+6.10
2026-08-15-6.34
2026-08-14-4.61
2026-08-13-1.38
2026-08-12+0.35
2026-08-11+3.15
2026-08-10+4.77
2026-08-09+3.38
2026-08-08+0.09
2026-08-07+2.03
2026-08-06-0.41
2026-08-05-3.63

Error distribution

Distribution of the signed daily error in °F for NCEP GFS at KTTN, lead day 4-10 to -9 °F: 0 days-9 to -8 °F: 0 days-8 to -7 °F: 0 days-7 to -6 °F: 1 day-6 to -5 °F: 1 day-5 to -4 °F: 1 day-4 to -3 °F: 1 day-3 to -2 °F: 1 day-2 to -1 °F: 3 days-1 to 0 °F: 2 days0 to 1 °F: 4 days1 to 2 °F: 1 day2 to 3 °F: 2 days3 to 4 °F: 3 days4 to 5 °F: 3 days5 to 6 °F: 0 days6 to 7 °F: 2 days7 to 8 °F: 0 days8 to 9 °F: 0 days9 to 10 °F: 1 daydashed: P50 |e| 2.76 · P90 |e| 6.11 °F-100+10 °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
-10.00-9.000
-9.00-8.000
-8.00-7.000
-7.00-6.001
-6.00-5.001
-5.00-4.001
-4.00-3.001
-3.00-2.001
-2.00-1.003
-1.00+0.002
+0.00+1.004
+1.00+2.001
+2.00+3.002
+3.00+4.003
+4.00+5.003
+5.00+6.000
+6.00+7.002
+7.00+8.000
+8.00+9.000
+9.00+10.001

Month by month

00Z bilinear daily maximum, newest first.

Monthn MAE °FBias °F
2026-08263.15 +1.01

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 +1.39 [0.26, 2.35] yes
GraphCast (IFS init) 25 +0.49 [-1.19, 1.81] no
ECMWF IFS HRES 20 -0.17 [-1.12, 1.12] no
Persistence (baseline) 26 -0.39 [-2.30, 1.77] no

Cite this page

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

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