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

San Francisco Intl · NCEP GFS · lead day 8

KSFO · 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 QC4.89 [3.66, 6.18]2.84-4.86 [-6.11, -3.66]5.95 [4.46, 7.10]18% [7%, 28%]18%32%-0.40+0.182026-08-09 → 2026-08-30
tmax00Zbilinear90d22 1 QC4.89 [3.40, 6.25]2.84-4.86 [-6.16, -3.40]5.95 [4.07, 7.22]18% [0%, 29%]18%32%-0.40+0.182026-08-09 → 2026-08-30
tmax00Zbilinear365d22 1 QC4.89 [3.33, 6.25]2.84-4.86 [-6.17, -3.33]5.95 [3.80, 7.31]18% [0%, 29%]18%32%-0.40+0.182026-08-09 → 2026-08-30
tmax00Zbilinearall22 1 QC4.89 [3.41, 6.25]2.84-4.86 [-6.16, -3.41]5.95 [4.07, 7.23]18% [0%, 29%]18%32%-0.40+0.182026-08-09 → 2026-08-30
tmax00Znearest30d22 1 QC2.98 [2.10, 3.89]2.98-0.27 [-1.25, 0.60]3.63 [2.70, 4.51]18% [6%, 33%]41%55%+0.15+0.142026-08-09 → 2026-08-30
tmax00Znearest90d22 1 QC2.98 [1.99, 3.99]2.98-0.27 [-1.31, 0.70]3.63 [2.54, 4.56]18% [0%, 33%]41%55%+0.15+0.142026-08-09 → 2026-08-30
tmax00Znearest365d22 1 QC2.98 [1.95, 4.03]2.98-0.27 [-1.29, 0.78]3.63 [2.50, 4.65]18% [0%, 36%]41%55%+0.15+0.142026-08-09 → 2026-08-30
tmax00Znearestall22 1 QC2.98 [1.98, 4.05]2.98-0.27 [-1.28, 0.68]3.63 [2.52, 4.67]18% [0%, 37%]41%55%+0.15+0.142026-08-09 → 2026-08-30
tmax12Zbilinear30d22 1 QC5.19 [3.79, 6.63]2.75-5.19 [-6.63, -3.79]6.13 [4.45, 7.46]5% [0%, 14%]14%32%-0.48+0.212026-08-09 → 2026-08-30
tmax12Zbilinear90d22 1 QC5.19 [3.44, 6.78]2.75-5.19 [-6.78, -3.44]6.13 [3.69, 7.49]5% [0%, 17%]14%32%-0.48+0.212026-08-09 → 2026-08-30
tmax12Zbilinear365d22 1 QC5.19 [3.38, 6.77]2.75-5.19 [-6.77, -3.38]6.13 [3.66, 7.52]5% [0%, 16%]14%32%-0.48+0.212026-08-09 → 2026-08-30
tmax12Zbilinearall22 1 QC5.19 [3.44, 6.72]2.75-5.19 [-6.72, -3.44]6.13 [3.71, 7.48]5% [0%, 16%]14%32%-0.48+0.212026-08-09 → 2026-08-30
tmax12Znearest30d22 1 QC2.71 [1.90, 3.61]2.79-0.48 [-1.68, 0.84]3.31 [2.38, 4.09]23% [6%, 37%]41%59%+0.22+0.192026-08-09 → 2026-08-30
tmax12Znearest90d22 1 QC2.71 [1.83, 3.67]2.79-0.48 [-1.86, 1.18]3.31 [2.23, 4.10]23% [4%, 38%]41%59%+0.22+0.192026-08-09 → 2026-08-30
tmax12Znearest365d22 1 QC2.71 [1.75, 3.64]2.79-0.48 [-1.83, 1.28]3.31 [2.12, 4.10]23% [0%, 39%]41%59%+0.22+0.192026-08-09 → 2026-08-30
tmax12Znearestall22 1 QC2.71 [1.82, 3.62]2.79-0.48 [-1.84, 1.31]3.31 [2.21, 4.11]23% [0%, 40%]41%59%+0.22+0.192026-08-09 → 2026-08-30
tmin00Zbilinear30d22 1 QC0.98 [0.71, 1.20]0.95-0.38 [-0.81, 0.17]1.29 [1.01, 1.48]59% [44%, 76%]82%100%-0.13-0.072026-08-09 → 2026-08-30
tmin00Zbilinear90d22 1 QC0.98 [0.62, 1.20]0.95-0.38 [-0.82, 0.16]1.29 [0.89, 1.48]59% [43%, 77%]82%100%-0.13-0.072026-08-09 → 2026-08-30
tmin00Zbilinear365d22 1 QC0.98 [0.59, 1.19]0.95-0.38 [-0.84, 0.21]1.29 [0.84, 1.49]59% [43%, 78%]82%100%-0.13-0.072026-08-09 → 2026-08-30
tmin00Zbilinearall22 1 QC0.98 [0.60, 1.19]0.95-0.38 [-0.82, 0.12]1.29 [0.82, 1.48]59% [43%, 80%]82%100%-0.13-0.072026-08-09 → 2026-08-30
tmin00Znearest30d22 1 QC2.14 [1.56, 2.65]1.21-1.97 [-2.64, -1.19]2.50 [1.94, 2.90]18% [5%, 32%]41%73%-1.48-0.372026-08-09 → 2026-08-30
tmin00Znearest90d22 1 QC2.14 [1.57, 2.72]1.21-1.97 [-2.70, -1.20]2.50 [1.95, 2.90]18% [0%, 31%]41%73%-1.48-0.372026-08-09 → 2026-08-30
tmin00Znearest365d22 1 QC2.14 [1.49, 2.72]1.21-1.97 [-2.68, -1.11]2.50 [1.87, 2.93]18% [0%, 31%]41%73%-1.48-0.372026-08-09 → 2026-08-30
tmin00Znearestall22 1 QC2.14 [1.61, 2.73]1.21-1.97 [-2.70, -1.27]2.50 [2.01, 2.91]18% [0%, 29%]41%73%-1.48-0.372026-08-09 → 2026-08-30
tmin12Zbilinear30d22 1 QC1.11 [0.75, 1.35]1.04-0.71 [-0.97, -0.29]1.47 [1.03, 1.74]50% [38%, 69%]86%91%-0.28-0.182026-08-09 → 2026-08-30
tmin12Zbilinear90d22 1 QC1.11 [0.61, 1.36]1.04-0.71 [-0.97, -0.22]1.47 [0.77, 1.75]50% [37%, 75%]86%91%-0.28-0.182026-08-09 → 2026-08-30
tmin12Zbilinear365d22 1 QC1.11 [0.59, 1.36]1.04-0.71 [-1.00, -0.22]1.47 [0.73, 1.75]50% [37%, 72%]86%91%-0.28-0.182026-08-09 → 2026-08-30
tmin12Zbilinearall22 1 QC1.11 [0.49, 1.37]1.04-0.71 [-0.98, -0.16]1.47 [0.71, 1.74]50% [36%, 75%]86%91%-0.28-0.182026-08-09 → 2026-08-30
tmin12Znearest30d22 1 QC2.34 [1.86, 2.64]1.11-2.34 [-2.64, -1.86]2.73 [2.10, 3.06]18% [7%, 32%]41%68%-1.70-0.262026-08-09 → 2026-08-30
tmin12Znearest90d22 1 QC2.34 [1.77, 2.63]1.11-2.34 [-2.63, -1.77]2.73 [1.98, 3.09]18% [0%, 33%]41%68%-1.70-0.262026-08-09 → 2026-08-30
tmin12Znearest365d22 1 QC2.34 [1.76, 2.65]1.11-2.34 [-2.65, -1.76]2.73 [1.98, 3.09]18% [0%, 33%]41%68%-1.70-0.262026-08-09 → 2026-08-30
tmin12Znearestall22 1 QC2.34 [1.76, 2.64]1.11-2.34 [-2.64, -1.76]2.73 [1.94, 3.11]18% [4%, 33%]41%68%-1.70-0.262026-08-09 → 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 KSFO, lead day 8, 00Z bilinear tmax+20+100-10-202026-08-09: -3.5 °F2026-08-10: -7.94 °F2026-08-11: -9.66 °F2026-08-12: -6.4 °F2026-08-13: -6.48 °F2026-08-14: -2.25 °F2026-08-15: -0.07 °F2026-08-16: -2.86 °F2026-08-17: -5.9 °F2026-08-18: -3.35 °F2026-08-19: -0.37 °F2026-08-20: -5.02 °F2026-08-21: -3.81 °F2026-08-22: -2.04 °F2026-08-23: -11.16 °F2026-08-24: -6.24 °F2026-08-25: +0.34 °F2026-08-26: -12.08 °F2026-08-27: -8.08 °F2026-08-28: -0.14 °F2026-08-29: -5.75 °F2026-08-30: -4.11 °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
2026-08-30-4.11
2026-08-29-5.75
2026-08-28-0.14
2026-08-27-8.08
2026-08-26-12.08
2026-08-25+0.34
2026-08-24-6.24
2026-08-23-11.16
2026-08-22-2.04
2026-08-21-3.81
2026-08-20-5.02
2026-08-19-0.37
2026-08-18-3.35
2026-08-17-5.90
2026-08-16-2.86
2026-08-15-0.07
2026-08-14-2.25
2026-08-13-6.48
2026-08-12-6.40
2026-08-11-9.66
2026-08-10-7.94
2026-08-09-3.50

Error distribution

Distribution of the signed daily error in °F for NCEP GFS at KSFO, 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: 1 day-12 to -10 °F: 1 day-10 to -8 °F: 2 days-8 to -6 °F: 4 days-6 to -4 °F: 4 days-4 to -2 °F: 6 days-2 to 0 °F: 3 days0 to 2 °F: 1 day2 to 4 °F: 0 days4 to 6 °F: 0 days6 to 8 °F: 0 days8 to 10 °F: 0 days10 to 12 °F: 0 days12 to 14 °F: 0 days14 to 16 °F: 0 days16 to 18 °F: 0 days18 to 20 °F: 0 daysdashed: P50 |e| 4.57 · P90 |e| 9.5 °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
-14.00-12.001
-12.00-10.001
-10.00-8.002
-8.00-6.004
-6.00-4.004
-4.00-2.006
-2.00+0.003
+0.00+2.001
+2.00+4.000
+4.00+6.000
+6.00+8.000
+8.00+10.000
+10.00+12.000
+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
2026-08224.89 -4.86

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 -0.47 [-1.62, 0.46] no
GraphCast (IFS init) 22 -1.87 [-2.92, -0.74] yes
ECMWF IFS HRES 17 -0.97 [-1.61, -0.34] yes
Persistence (baseline) 22 +1.39 [-0.04, 3.04] no

Cite this page

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

LongCastCheck (2026). Station-level verification of raw weather-model 2 m temperature forecasts: KSFO (San Francisco Intl), 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/KSFO/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