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

Seattle-Tacoma · NCEP GFS · lead day 8

KSEA · 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 QC7.29 [4.08, 10.50]6.82+1.83 [-2.05, 5.62]8.99 [5.08, 11.95]9% [0%, 22%]18%32%-0.33-0.242026-08-09 → 2026-08-30
tmax00Zbilinear90d22 1 QC7.29 [3.80, 10.50]6.82+1.83 [-2.37, 6.10]8.99 [4.69, 11.97]9% [0%, 23%]18%32%-0.33-0.242026-08-09 → 2026-08-30
tmax00Zbilinear365d22 1 QC7.29 [3.74, 11.12]6.82+1.83 [-2.60, 6.49]8.99 [4.63, 12.57]9% [0%, 25%]18%32%-0.33-0.242026-08-09 → 2026-08-30
tmax00Zbilinearall22 1 QC7.29 [3.80, 10.96]6.82+1.83 [-2.21, 6.39]8.99 [4.73, 12.24]9% [0%, 25%]18%32%-0.33-0.242026-08-09 → 2026-08-30
tmax00Znearest30d22 1 QC7.14 [4.00, 10.33]6.78+1.71 [-1.90, 5.32]8.79 [4.86, 11.71]14% [4%, 26%]23%23%-0.30-0.232026-08-09 → 2026-08-30
tmax00Znearest90d22 1 QC7.14 [3.79, 10.43]6.78+1.71 [-2.07, 5.64]8.79 [4.61, 11.79]14% [0%, 27%]23%23%-0.30-0.232026-08-09 → 2026-08-30
tmax00Znearest365d22 1 QC7.14 [3.75, 10.92]6.78+1.71 [-2.40, 6.13]8.79 [4.62, 12.33]14% [0%, 29%]23%23%-0.30-0.232026-08-09 → 2026-08-30
tmax00Znearestall22 1 QC7.14 [3.81, 10.66]6.78+1.71 [-1.98, 6.01]8.79 [4.69, 11.93]14% [0%, 27%]23%23%-0.30-0.232026-08-09 → 2026-08-30
tmax12Zbilinear30d22 1 QC5.09 [2.87, 7.30]4.84+1.68 [-1.21, 4.87]6.89 [3.84, 9.13]9% [0%, 20%]36%45%+0.07+0.122026-08-09 → 2026-08-30
tmax12Zbilinear90d22 1 QC5.09 [2.57, 7.27]4.84+1.68 [-1.41, 5.04]6.89 [3.41, 9.07]9% [0%, 22%]36%45%+0.07+0.122026-08-09 → 2026-08-30
tmax12Zbilinear365d22 1 QC5.09 [2.49, 7.53]4.84+1.68 [-1.50, 5.11]6.89 [3.29, 9.29]9% [0%, 22%]36%45%+0.07+0.122026-08-09 → 2026-08-30
tmax12Zbilinearall22 1 QC5.09 [2.55, 7.33]4.84+1.68 [-1.44, 5.27]6.89 [3.28, 9.20]9% [0%, 22%]36%45%+0.07+0.122026-08-09 → 2026-08-30
tmax12Znearest30d22 1 QC4.86 [2.64, 7.15]4.67+1.20 [-1.63, 4.41]6.65 [3.59, 8.93]18% [5%, 29%]36%50%+0.12+0.152026-08-09 → 2026-08-30
tmax12Znearest90d22 1 QC4.86 [2.35, 7.20]4.67+1.20 [-1.77, 4.55]6.65 [3.10, 8.91]18% [0%, 31%]36%50%+0.12+0.152026-08-09 → 2026-08-30
tmax12Znearest365d22 1 QC4.86 [2.28, 7.31]4.67+1.20 [-2.05, 4.65]6.65 [2.89, 9.09]18% [0%, 31%]36%50%+0.12+0.152026-08-09 → 2026-08-30
tmax12Znearestall22 1 QC4.86 [2.28, 7.17]4.67+1.20 [-1.82, 4.72]6.65 [2.98, 9.06]18% [0%, 33%]36%50%+0.12+0.152026-08-09 → 2026-08-30
tmin00Zbilinear30d22 1 QC3.04 [2.19, 4.24]3.04-0.46 [-3.18, 1.90]3.66 [2.39, 5.01]9% [0%, 22%]36%55%-0.36-0.362026-08-09 → 2026-08-30
tmin00Zbilinear90d22 1 QC3.04 [2.17, 4.48]3.04-0.46 [-3.69, 1.97]3.66 [2.36, 5.20]9% [0%, 23%]36%55%-0.36-0.362026-08-09 → 2026-08-30
tmin00Zbilinear365d22 1 QC3.04 [2.05, 4.49]3.04-0.46 [-3.91, 1.95]3.66 [2.28, 5.23]9% [0%, 25%]36%55%-0.36-0.362026-08-09 → 2026-08-30
tmin00Zbilinearall22 1 QC3.04 [2.06, 4.46]3.04-0.46 [-3.64, 2.13]3.66 [2.30, 5.19]9% [0%, 28%]36%55%-0.36-0.362026-08-09 → 2026-08-30
tmin00Znearest30d22 1 QC3.15 [2.42, 3.87]2.95+1.01 [-1.54, 3.34]3.67 [2.85, 4.31]14% [0%, 28%]27%45%-0.42-0.322026-08-09 → 2026-08-30
tmin00Znearest90d22 1 QC3.15 [2.34, 3.96]2.95+1.01 [-2.03, 3.37]3.67 [2.78, 4.34]14% [0%, 33%]27%45%-0.42-0.322026-08-09 → 2026-08-30
tmin00Znearest365d22 1 QC3.15 [2.29, 3.97]2.95+1.01 [-2.22, 3.42]3.67 [2.70, 4.35]14% [0%, 31%]27%45%-0.42-0.322026-08-09 → 2026-08-30
tmin00Znearestall22 1 QC3.15 [2.21, 4.02]2.95+1.01 [-2.03, 3.54]3.67 [2.61, 4.35]14% [0%, 31%]27%45%-0.42-0.322026-08-09 → 2026-08-30
tmin12Zbilinear30d22 1 QC2.40 [1.42, 3.65]2.19-1.50 [-3.36, 0.28]3.12 [1.70, 4.45]32% [14%, 48%]50%77%-0.08+0.022026-08-09 → 2026-08-30
tmin12Zbilinear90d22 1 QC2.40 [1.42, 4.04]2.19-1.50 [-3.86, 0.56]3.12 [1.72, 4.71]32% [9%, 50%]50%77%-0.08+0.022026-08-09 → 2026-08-30
tmin12Zbilinear365d22 1 QC2.40 [1.40, 4.10]2.19-1.50 [-3.89, 0.63]3.12 [1.67, 4.78]32% [5%, 52%]50%77%-0.08+0.022026-08-09 → 2026-08-30
tmin12Zbilinearall22 1 QC2.40 [1.37, 4.14]2.19-1.50 [-4.14, 0.59]3.12 [1.63, 4.82]32% [0%, 53%]50%77%-0.08+0.022026-08-09 → 2026-08-30
tmin12Znearest30d22 1 QC2.19 [1.73, 2.81]2.18+0.04 [-1.73, 1.72]2.75 [2.03, 3.56]23% [11%, 36%]50%77%+0.02+0.022026-08-09 → 2026-08-30
tmin12Znearest90d22 1 QC2.19 [1.74, 2.87]2.18+0.04 [-2.25, 2.00]2.75 [2.00, 3.65]23% [12%, 38%]50%77%+0.02+0.022026-08-09 → 2026-08-30
tmin12Znearest365d22 1 QC2.19 [1.74, 2.87]2.18+0.04 [-2.25, 2.06]2.75 [1.99, 3.69]23% [10%, 38%]50%77%+0.02+0.022026-08-09 → 2026-08-30
tmin12Znearestall22 1 QC2.19 [1.63, 2.84]2.18+0.04 [-2.37, 2.01]2.75 [1.89, 3.66]23% [10%, 38%]50%77%+0.02+0.022026-08-09 → 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 KSEA, lead day 8, 00Z bilinear tmax+20+100-10-202026-08-09: -0.39 °F2026-08-10: +5.63 °F2026-08-11: +8.86 °F2026-08-12: +4.06 °F2026-08-13: +8.96 °F2026-08-14: +8.09 °F2026-08-15: +12.68 °F2026-08-16: +10.26 °F2026-08-17: -19.66 °F2026-08-18: -16.98 °F2026-08-19: -0.46 °F2026-08-20: -13.63 °F2026-08-21: +10.26 °F2026-08-22: -5.58 °F2026-08-23: +11.24 °F2026-08-24: -1.15 °F2026-08-25: +2.05 °F2026-08-26: +2.85 °F2026-08-27: +1.53 °F2026-08-28: -2.17 °F2026-08-29: +6.78 °F2026-08-30: +7.07 °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+7.07
2026-08-29+6.78
2026-08-28-2.17
2026-08-27+1.53
2026-08-26+2.85
2026-08-25+2.05
2026-08-24-1.15
2026-08-23+11.24
2026-08-22-5.58
2026-08-21+10.26
2026-08-20-13.63
2026-08-19-0.46
2026-08-18-16.98
2026-08-17-19.66
2026-08-16+10.26
2026-08-15+12.68
2026-08-14+8.09
2026-08-13+8.96
2026-08-12+4.06
2026-08-11+8.86
2026-08-10+5.63
2026-08-09-0.39

Error distribution

Distribution of the signed daily error in °F for NCEP GFS at KSEA, lead day 8-20 to -18 °F: 1 day-18 to -16 °F: 1 day-16 to -14 °F: 0 days-14 to -12 °F: 1 day-12 to -10 °F: 0 days-10 to -8 °F: 0 days-8 to -6 °F: 0 days-6 to -4 °F: 1 day-4 to -2 °F: 1 day-2 to 0 °F: 3 days0 to 2 °F: 1 day2 to 4 °F: 2 days4 to 6 °F: 2 days6 to 8 °F: 2 days8 to 10 °F: 3 days10 to 12 °F: 3 days12 to 14 °F: 1 day14 to 16 °F: 0 days16 to 18 °F: 0 days18 to 20 °F: 0 daysdashed: P50 |e| 6.93 · P90 |e| 13.54 °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
-20.00-18.001
-18.00-16.001
-16.00-14.000
-14.00-12.001
-12.00-10.000
-10.00-8.000
-8.00-6.000
-6.00-4.001
-4.00-2.001
-2.00+0.003
+0.00+2.001
+2.00+4.002
+4.00+6.002
+6.00+8.002
+8.00+10.003
+10.00+12.003
+12.00+14.001
+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
2026-08227.29 +1.83

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 +0.90 [-1.99, 3.79] no
GraphCast (IFS init) 22 +0.72 [-2.94, 3.87] no
ECMWF IFS HRES 17 +1.20 [-1.51, 3.93] no
Persistence (baseline) 22 +1.79 [-3.65, 5.35] no

Cite this page

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

LongCastCheck (2026). Station-level verification of raw weather-model 2 m temperature forecasts: KSEA (Seattle-Tacoma), 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/KSEA/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