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

Boston Logan · NCEP GFS · lead day 4

KBOS · 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
tmax00Zbilinear30d25 1 QC4.21 [2.88, 5.26]4.46-1.39 [-2.98, 0.17]5.77 [4.20, 6.84]16% [4%, 28%]40%52%+0.37+0.332026-08-05 → 2026-08-30
tmax00Zbilinear90d25 1 QC4.21 [2.60, 5.49]4.46-1.39 [-3.26, 0.30]5.77 [3.77, 7.09]16% [0%, 29%]40%52%+0.37+0.332026-08-05 → 2026-08-30
tmax00Zbilinear365d25 1 QC4.21 [2.16, 5.68]4.46-1.39 [-3.32, 0.50]5.77 [2.93, 7.35]16% [0%, 29%]40%52%+0.37+0.332026-08-05 → 2026-08-30
tmax00Zbilinearall25 1 QC4.21 [2.45, 5.63]4.46-1.39 [-3.34, 0.37]5.77 [3.77, 7.22]16% [0%, 29%]40%52%+0.37+0.332026-08-05 → 2026-08-30
tmax00Znearest30d25 1 QC4.34 [2.78, 5.49]4.62-2.10 [-3.77, -0.48]6.13 [4.33, 7.35]24% [12%, 41%]40%48%+0.35+0.312026-08-05 → 2026-08-30
tmax00Znearest90d25 1 QC4.34 [2.54, 5.89]4.62-2.10 [-4.06, -0.42]6.13 [3.85, 7.82]24% [9%, 44%]40%48%+0.35+0.312026-08-05 → 2026-08-30
tmax00Znearest365d25 1 QC4.34 [1.96, 5.93]4.62-2.10 [-4.07, -0.17]6.13 [2.88, 7.81]24% [9%, 50%]40%48%+0.35+0.312026-08-05 → 2026-08-30
tmax00Znearestall25 1 QC4.34 [2.41, 5.84]4.62-2.10 [-4.12, -0.30]6.13 [3.80, 7.75]24% [9%, 47%]40%48%+0.35+0.312026-08-05 → 2026-08-30
tmax12Zbilinear30d25 1 QC3.99 [2.67, 4.98]4.12-0.94 [-2.47, 0.88]5.22 [3.56, 6.11]36% [19%, 48%]36%48%+0.40+0.382026-08-05 → 2026-08-30
tmax12Zbilinear90d25 1 QC3.99 [2.40, 4.98]4.12-0.94 [-2.44, 1.18]5.22 [2.84, 6.10]36% [20%, 50%]36%48%+0.40+0.382026-08-05 → 2026-08-30
tmax12Zbilinear365d25 1 QC3.99 [2.21, 5.00]4.12-0.94 [-2.62, 1.14]5.22 [2.70, 6.18]36% [19%, 50%]36%48%+0.40+0.382026-08-05 → 2026-08-30
tmax12Zbilinearall25 1 QC3.99 [2.27, 5.12]4.12-0.94 [-2.67, 1.00]5.22 [2.65, 6.27]36% [14%, 50%]36%48%+0.40+0.382026-08-05 → 2026-08-30
tmax12Znearest30d25 1 QC3.96 [2.36, 5.25]3.97-1.40 [-3.03, 0.54]5.33 [3.35, 6.47]20% [7%, 33%]44%52%+0.41+0.402026-08-05 → 2026-08-30
tmax12Znearest90d25 1 QC3.96 [1.85, 5.29]3.97-1.40 [-3.00, 0.86]5.33 [2.46, 6.50]20% [6%, 36%]44%52%+0.41+0.402026-08-05 → 2026-08-30
tmax12Znearest365d25 1 QC3.96 [1.73, 5.29]3.97-1.40 [-3.10, 0.83]5.33 [2.13, 6.53]20% [0%, 38%]44%52%+0.41+0.402026-08-05 → 2026-08-30
tmax12Znearestall25 1 QC3.96 [1.70, 5.37]3.97-1.40 [-3.08, 0.68]5.33 [1.87, 6.58]20% [0%, 36%]44%52%+0.41+0.402026-08-05 → 2026-08-30
tmin00Zbilinear30d25 1 QC1.75 [1.35, 2.09]1.44-1.19 [-1.80, -0.56]2.05 [1.58, 2.44]36% [21%, 57%]68%84%+0.41+0.502026-08-05 → 2026-08-30
tmin00Zbilinear90d25 1 QC1.75 [1.23, 2.15]1.44-1.19 [-1.96, -0.37]2.05 [1.43, 2.52]36% [22%, 63%]68%84%+0.41+0.502026-08-05 → 2026-08-30
tmin00Zbilinear365d25 1 QC1.75 [1.29, 2.16]1.44-1.19 [-2.02, -0.46]2.05 [1.46, 2.53]36% [21%, 60%]68%84%+0.41+0.502026-08-05 → 2026-08-30
tmin00Zbilinearall25 1 QC1.75 [1.23, 2.16]1.44-1.19 [-1.95, -0.37]2.05 [1.39, 2.51]36% [21%, 67%]68%84%+0.41+0.502026-08-05 → 2026-08-30
tmin00Znearest30d25 1 QC1.55 [1.28, 1.82]1.33-0.81 [-1.44, -0.20]1.82 [1.48, 2.17]32% [21%, 43%]68%92%+0.47+0.542026-08-05 → 2026-08-30
tmin00Znearest90d25 1 QC1.55 [1.23, 1.87]1.33-0.81 [-1.62, -0.00]1.82 [1.40, 2.21]32% [21%, 46%]68%92%+0.47+0.542026-08-05 → 2026-08-30
tmin00Znearest365d25 1 QC1.55 [1.24, 1.86]1.33-0.81 [-1.68, -0.08]1.82 [1.41, 2.26]32% [20%, 47%]68%92%+0.47+0.542026-08-05 → 2026-08-30
tmin00Znearestall25 1 QC1.55 [1.23, 1.86]1.33-0.81 [-1.62, -0.02]1.82 [1.41, 2.24]32% [19%, 46%]68%92%+0.47+0.542026-08-05 → 2026-08-30
tmin12Zbilinear30d25 1 QC2.62 [1.46, 3.36]2.24-1.85 [-2.58, -0.98]3.39 [2.18, 4.00]32% [17%, 57%]56%64%+0.12+0.222026-08-05 → 2026-08-30
tmin12Zbilinear90d25 1 QC2.62 [1.14, 3.39]2.24-1.85 [-2.58, -0.76]3.39 [1.70, 4.03]32% [17%, 60%]56%64%+0.12+0.222026-08-05 → 2026-08-30
tmin12Zbilinear365d25 1 QC2.62 [1.18, 3.45]2.24-1.85 [-2.65, -0.80]3.39 [1.75, 4.08]32% [14%, 60%]56%64%+0.12+0.222026-08-05 → 2026-08-30
tmin12Zbilinearall25 1 QC2.62 [0.95, 3.48]2.24-1.85 [-2.62, -0.75]3.39 [1.05, 4.09]32% [14%, 67%]56%64%+0.12+0.222026-08-05 → 2026-08-30
tmin12Znearest30d25 1 QC2.30 [1.39, 2.90]2.02-1.46 [-2.05, -0.77]2.99 [2.00, 3.49]36% [17%, 65%]52%72%+0.22+0.302026-08-05 → 2026-08-30
tmin12Znearest90d25 1 QC2.30 [1.04, 2.96]2.02-1.46 [-2.04, -0.64]2.99 [1.59, 3.53]36% [18%, 73%]52%72%+0.22+0.302026-08-05 → 2026-08-30
tmin12Znearest365d25 1 QC2.30 [1.02, 3.00]2.02-1.46 [-2.14, -0.63]2.99 [1.51, 3.55]36% [14%, 75%]52%72%+0.22+0.302026-08-05 → 2026-08-30
tmin12Znearestall25 1 QC2.30 [0.92, 3.03]2.02-1.46 [-2.12, -0.58]2.99 [1.38, 3.56]36% [14%, 78%]52%72%+0.22+0.302026-08-05 → 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 KBOS, lead day 4, 00Z bilinear tmax+20+100-10-202026-08-05: -13.21 °F2026-08-06: +1.85 °F2026-08-07: +2.16 °F2026-08-08: -5.34 °F2026-08-09: +1.35 °F2026-08-10: +3.52 °F2026-08-11: +0.23 °F2026-08-12: -9.9 °F2026-08-13: -3.97 °F2026-08-14: -12.97 °F2026-08-15: +2.03 °F2026-08-16: -0.93 °F2026-08-17: +2.15 °F2026-08-18: +1.69 °F2026-08-19: -3.38 °F2026-08-20: -13.02 °F2026-08-21: +5.83 °F2026-08-22: +4.77 °F2026-08-23: +6.58 °F2026-08-24: -4.88 °F2026-08-25: -0.83 °F2026-08-26: +1.32 °F2026-08-27: +0.31 °F2026-08-29: -1.61 °F2026-08-30: +1.44 °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+1.44
2026-08-29-1.61
2026-08-28—
2026-08-27+0.31
2026-08-26+1.32
2026-08-25-0.83
2026-08-24-4.88
2026-08-23+6.58
2026-08-22+4.77
2026-08-21+5.83
2026-08-20-13.02
2026-08-19-3.38
2026-08-18+1.69
2026-08-17+2.15
2026-08-16-0.93
2026-08-15+2.03
2026-08-14-12.97
2026-08-13-3.97
2026-08-12-9.90
2026-08-11+0.23
2026-08-10+3.52
2026-08-09+1.35
2026-08-08-5.34
2026-08-07+2.16
2026-08-06+1.85
2026-08-05-13.21

Error distribution

Distribution of the signed daily error in °F for NCEP GFS at KBOS, lead day 4-20 to -18 °F: 0 days-18 to -16 °F: 0 days-16 to -14 °F: 0 days-14 to -12 °F: 3 days-12 to -10 °F: 0 days-10 to -8 °F: 1 day-8 to -6 °F: 0 days-6 to -4 °F: 2 days-4 to -2 °F: 2 days-2 to 0 °F: 3 days0 to 2 °F: 7 days2 to 4 °F: 4 days4 to 6 °F: 2 days6 to 8 °F: 1 day8 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| 2.16 · P90 |e| 11.75 °F-200+20 °Fn = 25 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
-14.00-12.003
-12.00-10.000
-10.00-8.001
-8.00-6.000
-6.00-4.002
-4.00-2.002
-2.00+0.003
+0.00+2.007
+2.00+4.004
+4.00+6.002
+6.00+8.001
+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
2026-08254.21 -1.39

Availability

ModelScored period DaysCoverage
NCEP GFS2026-08-05 → 2026-08-30 25
NCEP GFS2026-08-05 → 2026-08-30 25
NCEP GFS2026-08-05 → 2026-08-30 25
NCEP GFS2026-08-05 → 2026-08-30 25

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 25 -0.05 [-1.46, 1.11] no
GraphCast (IFS init) 24 -0.11 [-1.86, 1.30] no
ECMWF IFS HRES 19 +0.87 [-0.64, 3.14] no
Persistence (baseline) 25 -2.47 [-5.48, 0.21] no

Cite this page

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

LongCastCheck (2026). Station-level verification of raw weather-model 2 m temperature forecasts: KBOS (Boston Logan), 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/KBOS/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