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

Phoenix Sky Harbor · NCEP GFS · lead day 4

KPHX · 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 QC3.49 [2.73, 4.43]2.21-3.14 [-4.22, -2.17]4.18 [3.16, 5.23]8% [0%, 21%]35%58%+0.37+0.602026-08-05 → 2026-08-30
tmax00Zbilinear90d26 1 QC3.49 [2.58, 4.73]2.21-3.14 [-4.57, -1.81]4.18 [2.94, 5.63]8% [0%, 22%]35%58%+0.37+0.602026-08-05 → 2026-08-30
tmax00Zbilinear365d26 1 QC3.49 [2.60, 4.91]2.21-3.14 [-4.81, -1.74]4.18 [2.95, 5.69]8% [0%, 22%]35%58%+0.37+0.602026-08-05 → 2026-08-30
tmax00Zbilinearall26 1 QC3.49 [2.53, 4.86]2.21-3.14 [-4.57, -1.74]4.18 [2.84, 5.67]8% [0%, 22%]35%58%+0.37+0.602026-08-05 → 2026-08-30
tmax00Znearest30d26 1 QC3.42 [2.70, 4.29]2.23-3.04 [-4.06, -2.06]4.11 [3.13, 5.09]4% [0%, 11%]38%58%+0.38+0.602026-08-05 → 2026-08-30
tmax00Znearest90d26 1 QC3.42 [2.60, 4.58]2.23-3.04 [-4.36, -1.75]4.11 [3.00, 5.40]4% [0%, 11%]38%58%+0.38+0.602026-08-05 → 2026-08-30
tmax00Znearest365d26 1 QC3.42 [2.61, 4.76]2.23-3.04 [-4.56, -1.72]4.11 [2.98, 5.48]4% [0%, 12%]38%58%+0.38+0.602026-08-05 → 2026-08-30
tmax00Znearestall26 1 QC3.42 [2.52, 4.67]2.23-3.04 [-4.36, -1.73]4.11 [2.86, 5.46]4% [0%, 12%]38%58%+0.38+0.602026-08-05 → 2026-08-30
tmax12Zbilinear30d26 1 QC4.16 [3.28, 5.02]2.09-3.87 [-4.72, -2.97]4.72 [3.71, 5.59]8% [0%, 18%]12%35%+0.25+0.632026-08-05 → 2026-08-30
tmax12Zbilinear90d26 1 QC4.16 [3.10, 5.24]2.09-3.87 [-5.04, -2.78]4.72 [3.50, 5.83]8% [0%, 18%]12%35%+0.25+0.632026-08-05 → 2026-08-30
tmax12Zbilinear365d26 1 QC4.16 [3.09, 5.46]2.09-3.87 [-5.35, -2.69]4.72 [3.53, 6.05]8% [0%, 20%]12%35%+0.25+0.632026-08-05 → 2026-08-30
tmax12Zbilinearall26 1 QC4.16 [3.09, 5.23]2.09-3.87 [-4.97, -2.78]4.72 [3.45, 5.86]8% [0%, 18%]12%35%+0.25+0.632026-08-05 → 2026-08-30
tmax12Znearest30d26 1 QC4.00 [3.14, 4.87]2.18-3.67 [-4.49, -2.80]4.61 [3.65, 5.42]12% [4%, 21%]23%38%+0.28+0.612026-08-05 → 2026-08-30
tmax12Znearest90d26 1 QC4.00 [2.90, 5.04]2.18-3.67 [-4.81, -2.64]4.61 [3.48, 5.62]12% [0%, 21%]23%38%+0.28+0.612026-08-05 → 2026-08-30
tmax12Znearest365d26 1 QC4.00 [2.98, 5.27]2.18-3.67 [-5.04, -2.59]4.61 [3.46, 5.80]12% [0%, 21%]23%38%+0.28+0.612026-08-05 → 2026-08-30
tmax12Znearestall26 1 QC4.00 [2.87, 5.08]2.18-3.67 [-4.75, -2.60]4.61 [3.37, 5.62]12% [0%, 21%]23%38%+0.28+0.612026-08-05 → 2026-08-30
tmin00Zbilinear30d26 1 QC4.17 [2.66, 5.61]2.88+3.93 [2.11, 5.49]5.37 [3.41, 6.93]23% [12%, 36%]35%42%+0.26+0.492026-08-05 → 2026-08-30
tmin00Zbilinear90d26 1 QC4.17 [2.26, 5.64]2.88+3.93 [1.55, 5.50]5.37 [3.04, 7.05]23% [12%, 40%]35%42%+0.26+0.492026-08-05 → 2026-08-30
tmin00Zbilinear365d26 1 QC4.17 [2.31, 5.66]2.88+3.93 [1.61, 5.57]5.37 [3.08, 7.09]23% [11%, 40%]35%42%+0.26+0.492026-08-05 → 2026-08-30
tmin00Zbilinearall26 1 QC4.17 [2.11, 5.71]2.88+3.93 [1.35, 5.60]5.37 [2.85, 7.16]23% [11%, 40%]35%42%+0.26+0.492026-08-05 → 2026-08-30
tmin00Znearest30d26 1 QC5.16 [3.42, 6.71]2.82+5.12 [3.33, 6.70]6.27 [4.18, 7.91]15% [3%, 30%]23%31%+0.09+0.502026-08-05 → 2026-08-30
tmin00Znearest90d26 1 QC5.16 [3.07, 6.74]2.82+5.12 [2.91, 6.72]6.27 [3.77, 8.01]15% [4%, 38%]23%31%+0.09+0.502026-08-05 → 2026-08-30
tmin00Znearest365d26 1 QC5.16 [2.93, 6.80]2.82+5.12 [2.77, 6.80]6.27 [3.78, 8.03]15% [0%, 38%]23%31%+0.09+0.502026-08-05 → 2026-08-30
tmin00Znearestall26 1 QC5.16 [2.88, 6.88]2.82+5.12 [2.69, 6.85]6.27 [3.63, 8.10]15% [0%, 38%]23%31%+0.09+0.502026-08-05 → 2026-08-30
tmin12Zbilinear30d26 1 QC3.93 [2.67, 5.15]3.02+3.54 [1.91, 4.98]5.19 [3.38, 6.75]19% [7%, 33%]42%46%+0.31+0.462026-08-05 → 2026-08-30
tmin12Zbilinear90d26 1 QC3.93 [2.48, 5.19]3.02+3.54 [1.53, 5.08]5.19 [3.14, 6.88]19% [7%, 37%]42%46%+0.31+0.462026-08-05 → 2026-08-30
tmin12Zbilinear365d26 1 QC3.93 [2.45, 5.18]3.02+3.54 [1.48, 5.11]5.19 [3.05, 6.89]19% [5%, 38%]42%46%+0.31+0.462026-08-05 → 2026-08-30
tmin12Zbilinearall26 1 QC3.93 [2.38, 5.27]3.02+3.54 [1.40, 5.20]5.19 [2.98, 6.88]19% [4%, 34%]42%46%+0.31+0.462026-08-05 → 2026-08-30
tmin12Znearest30d26 1 QC4.84 [3.25, 6.33]3.10+4.74 [3.00, 6.30]6.13 [4.20, 7.78]23% [7%, 45%]27%38%+0.14+0.452026-08-05 → 2026-08-30
tmin12Znearest90d26 1 QC4.84 [2.99, 6.44]3.10+4.74 [2.61, 6.37]6.13 [3.81, 7.88]23% [4%, 50%]27%38%+0.14+0.452026-08-05 → 2026-08-30
tmin12Znearest365d26 1 QC4.84 [2.83, 6.48]3.10+4.74 [2.62, 6.41]6.13 [3.77, 7.92]23% [0%, 50%]27%38%+0.14+0.452026-08-05 → 2026-08-30
tmin12Znearestall26 1 QC4.84 [2.95, 6.59]3.10+4.74 [2.53, 6.58]6.13 [3.73, 7.93]23% [0%, 50%]27%38%+0.14+0.452026-08-05 → 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 KPHX, lead day 4, 00Z bilinear tmax+10+50-5-102026-08-05: +1.77 °F2026-08-06: +1.24 °F2026-08-07: -3.18 °F2026-08-08: -5.68 °F2026-08-09: -2.78 °F2026-08-10: -1.39 °F2026-08-11: -2.2 °F2026-08-12: -1.96 °F2026-08-13: -2.32 °F2026-08-14: -1.28 °F2026-08-15: -4.02 °F2026-08-16: -4.53 °F2026-08-17: -4.39 °F2026-08-18: -5.15 °F2026-08-19: +1 °F2026-08-20: +0.48 °F2026-08-21: -7.55 °F2026-08-22: -6.12 °F2026-08-23: -2.38 °F2026-08-24: -1.86 °F2026-08-25: -2.64 °F2026-08-26: -5.67 °F2026-08-27: -1.31 °F2026-08-28: -2.76 °F2026-08-29: -8.94 °F2026-08-30: -8.13 °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
2026-08-30-8.13
2026-08-29-8.94
2026-08-28-2.76
2026-08-27-1.31
2026-08-26-5.67
2026-08-25-2.64
2026-08-24-1.86
2026-08-23-2.38
2026-08-22-6.12
2026-08-21-7.55
2026-08-20+0.48
2026-08-19+1.00
2026-08-18-5.15
2026-08-17-4.39
2026-08-16-4.53
2026-08-15-4.02
2026-08-14-1.28
2026-08-13-2.32
2026-08-12-1.96
2026-08-11-2.20
2026-08-10-1.39
2026-08-09-2.78
2026-08-08-5.68
2026-08-07-3.18
2026-08-06+1.24
2026-08-05+1.77

Error distribution

Distribution of the signed daily error in °F for NCEP GFS at KPHX, lead day 4-10 to -9 °F: 0 days-9 to -8 °F: 2 days-8 to -7 °F: 1 day-7 to -6 °F: 1 day-6 to -5 °F: 3 days-5 to -4 °F: 3 days-4 to -3 °F: 1 day-3 to -2 °F: 6 days-2 to -1 °F: 5 days-1 to 0 °F: 0 days0 to 1 °F: 2 days1 to 2 °F: 2 days2 to 3 °F: 0 days3 to 4 °F: 0 days4 to 5 °F: 0 days5 to 6 °F: 0 days6 to 7 °F: 0 days7 to 8 °F: 0 days8 to 9 °F: 0 days9 to 10 °F: 0 daysdashed: P50 |e| 2.7 · P90 |e| 6.84 °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
-9.00-8.002
-8.00-7.001
-7.00-6.001
-6.00-5.003
-5.00-4.003
-4.00-3.001
-3.00-2.006
-2.00-1.005
-1.00+0.000
+0.00+1.002
+1.00+2.002
+2.00+3.000
+3.00+4.000
+4.00+5.000
+5.00+6.000
+6.00+7.000
+7.00+8.000
+8.00+9.000
+9.00+10.000

Month by month

00Z bilinear daily maximum, newest first.

Monthn MAE °FBias °F
2026-08263.49 -3.14

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 -0.32 [-1.72, 0.89] no
GraphCast (IFS init) 25 -0.70 [-1.59, 0.24] no
ECMWF IFS HRES 20 +0.79 [-0.34, 1.96] no
Persistence (baseline) 26 -2.05 [-4.76, 0.96] no

Cite this page

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

LongCastCheck (2026). Station-level verification of raw weather-model 2 m temperature forecasts: KPHX (Phoenix Sky Harbor), 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/KPHX/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