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 8

KTTN · 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 QC4.79 [3.87, 5.42]4.74+0.57 [-1.95, 3.34]5.55 [4.34, 6.27]5% [0%, 16%]9%23%-0.27-0.502026-08-09 → 2026-08-30
tmax00Zbilinear90d22 1 QC4.79 [3.66, 5.42]4.74+0.57 [-2.06, 3.63]5.55 [3.92, 6.28]5% [0%, 20%]9%23%-0.27-0.502026-08-09 → 2026-08-30
tmax00Zbilinear365d22 1 QC4.79 [3.57, 5.45]4.74+0.57 [-2.21, 3.82]5.55 [3.88, 6.31]5% [0%, 18%]9%23%-0.27-0.502026-08-09 → 2026-08-30
tmax00Zbilinearall22 1 QC4.79 [3.77, 5.41]4.74+0.57 [-2.34, 4.15]5.55 [4.03, 6.30]5% [0%, 18%]9%23%-0.27-0.502026-08-09 → 2026-08-30
tmax00Znearest30d22 1 QC5.00 [3.97, 5.72]4.90+1.03 [-1.57, 3.84]5.81 [4.58, 6.58]9% [0%, 20%]9%27%-0.32-0.562026-08-09 → 2026-08-30
tmax00Znearest90d22 1 QC5.00 [3.87, 5.74]4.90+1.03 [-1.66, 4.14]5.81 [4.33, 6.59]9% [0%, 22%]9%27%-0.32-0.562026-08-09 → 2026-08-30
tmax00Znearest365d22 1 QC5.00 [3.67, 5.77]4.90+1.03 [-1.80, 4.35]5.81 [4.18, 6.65]9% [0%, 20%]9%27%-0.32-0.562026-08-09 → 2026-08-30
tmax00Znearestall22 1 QC5.00 [3.84, 5.74]4.90+1.03 [-1.95, 4.72]5.81 [4.33, 6.64]9% [0%, 20%]9%27%-0.32-0.562026-08-09 → 2026-08-30
tmax12Zbilinear30d22 1 QC4.44 [3.28, 5.80]4.08+1.89 [-0.10, 4.32]5.49 [3.99, 6.66]9% [0%, 22%]27%45%-0.18-0.302026-08-09 → 2026-08-30
tmax12Zbilinear90d22 1 QC4.44 [3.24, 6.27]4.08+1.89 [-0.16, 4.51]5.49 [3.78, 6.95]9% [0%, 22%]27%45%-0.18-0.302026-08-09 → 2026-08-30
tmax12Zbilinear365d22 1 QC4.44 [3.15, 6.36]4.08+1.89 [-0.44, 4.59]5.49 [3.73, 6.91]9% [0%, 25%]27%45%-0.18-0.302026-08-09 → 2026-08-30
tmax12Zbilinearall22 1 QC4.44 [3.12, 6.62]4.08+1.89 [-0.33, 5.23]5.49 [3.62, 7.11]9% [0%, 29%]27%45%-0.18-0.302026-08-09 → 2026-08-30
tmax12Znearest30d22 1 QC4.80 [3.63, 6.23]4.15+2.41 [0.49, 4.89]5.79 [4.21, 7.06]9% [0%, 22%]18%45%-0.27-0.322026-08-09 → 2026-08-30
tmax12Znearest90d22 1 QC4.80 [3.58, 6.70]4.15+2.41 [0.44, 5.17]5.79 [4.07, 7.28]9% [0%, 22%]18%45%-0.27-0.322026-08-09 → 2026-08-30
tmax12Znearest365d22 1 QC4.80 [3.51, 6.70]4.15+2.41 [0.21, 5.29]5.79 [3.95, 7.28]9% [0%, 25%]18%45%-0.27-0.322026-08-09 → 2026-08-30
tmax12Znearestall22 1 QC4.80 [3.49, 7.08]4.15+2.41 [0.27, 5.67]5.79 [3.93, 7.52]9% [0%, 29%]18%45%-0.27-0.322026-08-09 → 2026-08-30
tmin00Zbilinear30d22 1 QC4.60 [2.87, 6.30]3.62+3.47 [0.86, 6.06]5.62 [3.48, 7.29]14% [0%, 29%]27%36%+0.04+0.022026-08-09 → 2026-08-30
tmin00Zbilinear90d22 1 QC4.60 [2.73, 6.38]3.62+3.47 [0.82, 6.19]5.62 [3.20, 7.36]14% [0%, 29%]27%36%+0.04+0.022026-08-09 → 2026-08-30
tmin00Zbilinear365d22 1 QC4.60 [2.71, 6.57]3.62+3.47 [0.53, 6.22]5.62 [3.17, 7.45]14% [0%, 29%]27%36%+0.04+0.022026-08-09 → 2026-08-30
tmin00Zbilinearall22 1 QC4.60 [2.60, 6.62]3.62+3.47 [0.49, 6.36]5.62 [3.03, 7.59]14% [0%, 29%]27%36%+0.04+0.022026-08-09 → 2026-08-30
tmin00Znearest30d22 1 QC4.73 [2.97, 6.44]3.81+3.54 [0.79, 6.23]5.77 [3.65, 7.43]9% [0%, 18%]27%36%+0.01-0.032026-08-09 → 2026-08-30
tmin00Znearest90d22 1 QC4.73 [2.85, 6.53]3.81+3.54 [0.73, 6.30]5.77 [3.40, 7.48]9% [0%, 19%]27%36%+0.01-0.032026-08-09 → 2026-08-30
tmin00Znearest365d22 1 QC4.73 [2.82, 6.68]3.81+3.54 [0.49, 6.30]5.77 [3.35, 7.61]9% [0%, 18%]27%36%+0.01-0.032026-08-09 → 2026-08-30
tmin00Znearestall22 1 QC4.73 [2.71, 6.72]3.81+3.54 [0.46, 6.62]5.77 [3.21, 7.67]9% [0%, 19%]27%36%+0.01-0.032026-08-09 → 2026-08-30
tmin12Zbilinear30d22 1 QC5.35 [4.38, 6.80]4.37+3.52 [0.59, 6.55]6.37 [5.13, 7.98]14% [0%, 29%]14%27%-0.12-0.182026-08-09 → 2026-08-30
tmin12Zbilinear90d22 1 QC5.35 [4.40, 7.06]4.37+3.52 [0.54, 6.86]6.37 [4.96, 8.28]14% [0%, 29%]14%27%-0.12-0.182026-08-09 → 2026-08-30
tmin12Zbilinear365d22 1 QC5.35 [4.28, 7.05]4.37+3.52 [0.23, 6.77]6.37 [4.82, 8.41]14% [0%, 31%]14%27%-0.12-0.182026-08-09 → 2026-08-30
tmin12Zbilinearall22 1 QC5.35 [4.31, 7.57]4.37+3.52 [0.24, 7.32]6.37 [4.85, 8.68]14% [0%, 31%]14%27%-0.12-0.182026-08-09 → 2026-08-30
tmin12Znearest30d22 1 QC5.47 [4.47, 6.95]4.43+3.67 [0.73, 6.75]6.50 [5.25, 8.13]14% [0%, 29%]14%27%-0.15-0.202026-08-09 → 2026-08-30
tmin12Znearest90d22 1 QC5.47 [4.50, 7.21]4.43+3.67 [0.68, 7.05]6.50 [5.16, 8.39]14% [0%, 29%]14%27%-0.15-0.202026-08-09 → 2026-08-30
tmin12Znearest365d22 1 QC5.47 [4.37, 7.20]4.43+3.67 [0.37, 6.98]6.50 [5.02, 8.55]14% [0%, 31%]14%27%-0.15-0.202026-08-09 → 2026-08-30
tmin12Znearestall22 1 QC5.47 [4.38, 7.70]4.43+3.67 [0.36, 7.48]6.50 [5.04, 8.80]14% [0%, 31%]14%27%-0.15-0.202026-08-09 → 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 KTTN, lead day 8, 00Z bilinear tmax+20+100-10-202026-08-09: +4.15 °F2026-08-10: -0.73 °F2026-08-11: +4.29 °F2026-08-12: -5.36 °F2026-08-13: -11.74 °F2026-08-14: +5.12 °F2026-08-15: -2.8 °F2026-08-16: +2.43 °F2026-08-17: -4.22 °F2026-08-18: -3.08 °F2026-08-19: -1.24 °F2026-08-20: +6.84 °F2026-08-21: +3.2 °F2026-08-22: +11.72 °F2026-08-23: +3.84 °F2026-08-24: +7.8 °F2026-08-25: +2.51 °F2026-08-26: +3.17 °F2026-08-27: -5.93 °F2026-08-28: -7.47 °F2026-08-29: +3.83 °F2026-08-30: -3.9 °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
2026-08-30-3.90
2026-08-29+3.83
2026-08-28-7.47
2026-08-27-5.93
2026-08-26+3.17
2026-08-25+2.51
2026-08-24+7.80
2026-08-23+3.84
2026-08-22+11.72
2026-08-21+3.20
2026-08-20+6.84
2026-08-19-1.24
2026-08-18-3.08
2026-08-17-4.22
2026-08-16+2.43
2026-08-15-2.80
2026-08-14+5.12
2026-08-13-11.74
2026-08-12-5.36
2026-08-11+4.29
2026-08-10-0.73
2026-08-09+4.15

Error distribution

Distribution of the signed daily error in °F for NCEP GFS at KTTN, lead day 8-20 to -18 °F: 0 days-18 to -16 °F: 0 days-16 to -14 °F: 0 days-14 to -12 °F: 0 days-12 to -10 °F: 1 day-10 to -8 °F: 0 days-8 to -6 °F: 1 day-6 to -4 °F: 3 days-4 to -2 °F: 3 days-2 to 0 °F: 2 days0 to 2 °F: 0 days2 to 4 °F: 6 days4 to 6 °F: 3 days6 to 8 °F: 2 days8 to 10 °F: 0 days10 to 12 °F: 1 day12 to 14 °F: 0 days14 to 16 °F: 0 days16 to 18 °F: 0 days18 to 20 °F: 0 daysdashed: P50 |e| 4.02 · P90 |e| 7.77 °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
-16.00-14.000
-14.00-12.000
-12.00-10.001
-10.00-8.000
-8.00-6.001
-6.00-4.003
-4.00-2.003
-2.00+0.002
+0.00+2.000
+2.00+4.006
+4.00+6.003
+6.00+8.002
+8.00+10.000
+10.00+12.001
+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
2026-08224.79 +0.57

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 +2.60 [1.56, 3.51] yes
GraphCast (IFS init) 22 +1.35 [-0.33, 2.29] no
ECMWF IFS HRES 17 +1.92 [0.32, 3.33] yes
Persistence (baseline) 22 +1.02 [-0.62, 2.57] no

Cite this page

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

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