Daily verification · methodology v0.3.1

How far off was each weather model?

Over the last 90 days, across 23 U.S. stations, the most accurate raw sampled daily minimum forecast 1 day ahead is GraphCast (IFS init): mean absolute error 2.29 °F [2.21, 2.37], bias −1.27 °F, on n = 70 scored days.

Scope: raw model output on the native 0.25° grid. This view scores the sampled daily minimum against the minimum of the four *observed* samples on the same day. Errors are computed in °C and shown in °F (methodology v0.3.1).

Window
the last 90 days
Variable
sampled daily minimum
Init
12Z
Interpolation
bilinear
Data through
2026-08-30
Updated
Next update

Leader, lead day 1

2.29°F

[2.21, 2.37] MAE

GraphCast (IFS init)

Persistence baseline

2.43°F

[2.30, 2.56]

yesterday's observation — the bar every model has to clear

Scored days

70

23 stations · 12 systems

in the last 90 days, lead day 1

Systems ranked

1/12

next update

below n = 30: published, greyed, unranked

Mean absolute error with 95 % confidence intervals

Lead day 1 · the last 90 days · 23 stations pooled · 12Z · bilinear · sampled daily minimum. Whiskers are moving-block bootstrap intervals; models whose whiskers overlap are not distinguishable at this sample size. Baselines are drawn in grey and never ranked.

MAE by model with 95 % confidence intervals, lead day 1, 90d, 12Z, bilinear012345mean absolute error, °FGraphCast (IFS init)GraphCast (IFS init): 2.29 °F2.29FourCastNet v2 (IFS init)FourCastNet v2 (IFS init): 2.03 °F2.03FourCastNet v2 (GFS init)FourCastNet v2 (GFS init): 2.11 °F2.11Aurora (GFS init)Aurora (GFS init): 2.14 °F2.14ECMWF IFS HRESECMWF IFS HRES: 2.18 °F2.18GraphCast (GFS init)GraphCast (GFS init): 2.19 °F2.19Pangu-Weather (GFS init)Pangu-Weather (GFS init): 2.2 °F2.2Aurora (IFS init)Aurora (IFS init): 2.22 °F2.22ECMWF AIFS SingleECMWF AIFS Single: 2.28 °F2.28Pangu-Weather (IFS init)Pangu-Weather (IFS init): 2.3 °F2.3NCEP GFSNCEP GFS: 2.4 °F2.4Persistence (baseline)Persistence (baseline): 2.43 °F2.43

Source: CastCheck 0.1.0, methodology v0.3.1 · ECMWF open data, NOAA/NCEP GFS, NOAA/CIRA AIWP, NWS ASOS · data through 2026-08-30 · CC BY 4.0. Hover a bar for its value.

Lead day 1target = init + 1 d

permalink

The last 90 days, all 23 stations pooled, 12Z initialization, bilinear interpolation, sampled daily minimum against the minimum of the four *observed* samples on the same day. Lower MAE is better; bias is positive when the model is too warm. Every number links to its permanent page.

Skill is 1 − MAE ÷ MAE(persistence) computed on the days both have a value — the small print in that column is that denominator and the size of the intersection, so the number can be checked against the persistence row rather than contradicting it. The persistence row's own n is its whole record, marked all days. Skill, debiased (out-of-sample) repeats the score after removing a bias estimated on the 30 scored days before each day and applied forward, never on the day itself. An interval reads when the bootstrap could not run: fewer than 28 scored days or fewer than 4 blocks. Hit-rate intervals are Wilson score intervals, not bootstraps.

Lead day 1, the last 90 days, 12Z, bilinear, sampled daily minimum.
RankModelMAE °FBias °F±3 °F SkillSkill, debiased (out-of-sample) nvs leader
1GraphCast (IFS init)graphcast_ifs2.29[2.21, 2.37]−1.27[−1.40, −1.13]70% +0.05[+0.01, +0.10]vs 2.42 (n=70)+0.37n=70 7022.7 stns lowest MAE in this view
FourCastNet v2 (IFS init)fourcastnet_ifs2.03−0.0285% vs 2.54 (n=2)n=0 219 stns
FourCastNet v2 (GFS init)fourcastnet_gfs2.11+0.3381% vs 2.54 (n=2)n=0 219 stns
Aurora (GFS init)aurora_gfs2.14−0.2070% vs 2.54 (n=2)n=0 219 stns
ECMWF IFS HRESifs_hres2.18[2.02, 2.35]−0.55[−0.75, −0.35]76% +0.07[−0.03, +0.15]vs 2.34 (n=29)+0.37n=14 2922.7 stns
GraphCast (GFS init)graphcast_gfs2.19+0.1874% vs 2.54 (n=2)n=2 219 stns
Pangu-Weather (GFS init)pangu_gfs2.20+0.1575% vs 2.54 (n=2)n=0 219 stns
Aurora (IFS init)aurora_ifs2.22−0.8568% vs 2.54 (n=2)n=0 219 stns
ECMWF AIFS Singleaifs_single2.28[2.09, 2.44]−1.33[−1.54, −1.14]73% +0.02[−0.01, +0.06]vs 2.34 (n=29)+0.35n=14 2922.7 stns
Pangu-Weather (IFS init)pangu_ifs2.30−0.9975% vs 2.54 (n=2)n=0 219 stns
NCEP GFSgfs2.40[2.21, 2.61]+0.17[−0.09, 0.45]68% −0.03[−0.14, +0.08]vs 2.34 (n=29)+0.29n=14 2922.7 stns
Persistence (baseline)persistence · baseline2.43[2.30, 2.56]−0.05[−0.19, 0.09]71% 74all days

+ model too warm − model too cold bias interval includes zero ★ lowest MAE = not distinguishable from the leader ▼ worse than the leader ▲ better than the leader — all three Holm-corrected within this table, over the family of comparisons against the leader; the uncorrected verdict for every pair is published in the pairwise table of each permanent link and in pairwise_latest.csv.gzn < 30 greyed and unranked CI is a 95 % moving-block bootstrap interval on the group's own days, and reads — when it could not be computed skill reads — when fewer than 10 days are common to the model and the baseline: the ratio of two means over a handful of shared days is not a number worth printing

Lead day 3target = init + 3 d

permalink

Same sampling as lead day 1. Skill is 1 − MAE ÷ MAE(persistence) on the days both have a value.

Lead day 3, the last 90 days, 12Z, bilinear, sampled daily minimum.
RankModelMAE °FBias °FSkillnvs leader
1GraphCast (IFS init)graphcast_ifs2.40[2.32, 2.49]−1.29[−1.49, −1.10]+0.31[+0.25, +0.36]vs 3.48 (n=68)6822.9 stns lowest MAE in this view
ECMWF IFS HRESifs_hres2.34−0.24+0.25vs 3.14 (n=27)2722.6 stns
ECMWF AIFS Singleaifs_single2.40−1.15+0.24vs 3.14 (n=27)2722.6 stns
NCEP GFSgfs2.77+0.50+0.12vs 3.14 (n=27)2722.6 stns
Persistence (baseline)persistence · baseline3.50[3.22, 3.80]−0.18[−0.55, 0.14]74all days

Lead day 5target = init + 5 d

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Same sampling as lead day 1. Skill is 1 − MAE ÷ MAE(persistence) on the days both have a value.

Lead day 5, the last 90 days, 12Z, bilinear, sampled daily minimum.
RankModelMAE °FBias °FSkillnvs leader
1GraphCast (IFS init)graphcast_ifs2.60[2.49, 2.69]−1.21[−1.36, −1.04]+0.29[+0.21, +0.37]vs 3.65 (n=68)6822.8 stns lowest MAE in this view
ECMWF IFS HRESifs_hres2.61−0.01+0.19vs 3.23 (n=25)2522.6 stns
ECMWF AIFS Singleaifs_single2.62−1.22+0.19vs 3.23 (n=25)2522.6 stns
NCEP GFSgfs2.95+0.29+0.09vs 3.23 (n=25)2522.6 stns
Persistence (baseline)persistence · baseline3.68[3.32, 4.16]−0.18[−0.72, 0.26]74all days

Lead day 7target = init + 7 d

permalink

Same sampling as lead day 1. Skill is 1 − MAE ÷ MAE(persistence) on the days both have a value.

Lead day 7, the last 90 days, 12Z, bilinear, sampled daily minimum.
RankModelMAE °FBias °FSkillnvs leader
1GraphCast (IFS init)graphcast_ifs2.87[2.67, 3.07]−1.22[−1.42, −1.04]+0.29[+0.21, +0.37]vs 4.01 (n=66)6622.8 stns lowest MAE in this view
ECMWF AIFS Singleaifs_single2.77−1.27+0.23vs 3.61 (n=23)2322.6 stns
ECMWF IFS HRESifs_hres2.89+0.25+0.20vs 3.61 (n=23)2322.6 stns
NCEP GFSgfs3.33+0.22+0.08vs 3.61 (n=23)2322.6 stns
Persistence (baseline)persistence · baseline3.96[3.61, 4.35]−0.17[−0.88, 0.42]74all days

The same four samples as a daily maximum and minimum

Lead day 1, the last 90 days, 12Z, bilinear. Here the forecast's max/min of the four samples is scored against the observation's max/min of the same four instants. Like for like: whatever the four-sample definition misses, it misses on both sides. The comparison against the true NWS daily extremes is a different question and lives on the station and permanent-link pages.

Sampled daily maximumtmax_s

RankModelMAE °FBias °FSkillnvs leader
1GraphCast (IFS init)graphcast_ifs2.85[2.68, 3.01]−2.30[−2.54, −2.08]+0.10vs 3.15 (n=70)70
ECMWF AIFS Singleaifs_single2.04[1.98, 2.11]−0.38[−0.49, −0.27]+0.27vs 2.80 (n=29)29
ECMWF IFS HRESifs_hres2.19[2.07, 2.31]−0.52[−0.64, −0.40]+0.22vs 2.80 (n=29)29
Pangu-Weather (IFS init)pangu_ifs2.46−0.42vs 3.48 (n=2)2
FourCastNet v2 (GFS init)fourcastnet_gfs2.55−1.09vs 3.48 (n=2)2
FourCastNet v2 (IFS init)fourcastnet_ifs2.60−1.31vs 3.48 (n=2)2
Pangu-Weather (GFS init)pangu_gfs2.93−0.58vs 3.48 (n=2)2
Persistence (baseline)persistence3.18[2.90, 3.44]−0.06[−0.25, 0.13]74all days
NCEP GFSgfs3.19[2.97, 3.37]+1.88[1.57, 2.20]−0.14vs 2.80 (n=29)29
Aurora (IFS init)aurora_ifs3.46−3.30vs 3.48 (n=2)2
GraphCast (GFS init)graphcast_gfs3.72−3.37vs 3.48 (n=2)2
Aurora (GFS init)aurora_gfs4.24−4.11vs 3.48 (n=2)2

Sampled daily minimumtmin_s

RankModelMAE °FBias °FSkillnvs leader
1GraphCast (IFS init)graphcast_ifs2.29[2.21, 2.37]−1.27[−1.40, −1.13]+0.05vs 2.42 (n=70)70
FourCastNet v2 (IFS init)fourcastnet_ifs2.03−0.02vs 2.54 (n=2)2
FourCastNet v2 (GFS init)fourcastnet_gfs2.11+0.33vs 2.54 (n=2)2
Aurora (GFS init)aurora_gfs2.14−0.20vs 2.54 (n=2)2
ECMWF IFS HRESifs_hres2.18[2.02, 2.35]−0.55[−0.75, −0.35]+0.07vs 2.34 (n=29)29
GraphCast (GFS init)graphcast_gfs2.19+0.18vs 2.54 (n=2)2
Pangu-Weather (GFS init)pangu_gfs2.20+0.15vs 2.54 (n=2)2
Aurora (IFS init)aurora_ifs2.22−0.85vs 2.54 (n=2)2
ECMWF AIFS Singleaifs_single2.28[2.09, 2.44]−1.33[−1.54, −1.14]+0.02vs 2.34 (n=29)29
Pangu-Weather (IFS init)pangu_ifs2.30−0.99vs 2.54 (n=2)2
NCEP GFSgfs2.40[2.21, 2.61]+0.17[−0.09, 0.45]−0.03vs 2.34 (n=29)29
Persistence (baseline)persistence2.43[2.30, 2.56]−0.05[−0.19, 0.09]74all days

Every model × every lead day

MAE in °F with the bias and n underneath, the last 90 days, 12Z, bilinear, sampled daily minimum. The sparkline is the same model's MAE across lead days 1–9 on a shared vertical scale.

Modeld1d2d3d4d5d6d7d8d9 lead 1–9
ECMWF AIFS Singleaifs_single2.28−1.33 · n=292.30−1.18 · n=282.40−1.15 · n=272.51−1.19 · n=262.62−1.22 · n=252.78−1.22 · n=242.77−1.27 · n=232.86−1.43 · n=223.17−1.71 · n=21ECMWF AIFS Single MAE by lead day 1 to 9
Aurora (GFS init)aurora_gfs2.14−0.20 · n=22.15−0.13 · n=1 Aurora (GFS init) MAE by lead day 1 to 9
Aurora (IFS init)aurora_ifs2.22−0.85 · n=22.45−0.82 · n=1 Aurora (IFS init) MAE by lead day 1 to 9
FourCastNet v2 (GFS init)fourcastnet_gfs2.11+0.33 · n=22.40+1.08 · n=1 FourCastNet v2 (GFS init) MAE by lead day 1 to 9
FourCastNet v2 (IFS init)fourcastnet_ifs2.03−0.02 · n=22.06+0.85 · n=1 FourCastNet v2 (IFS init) MAE by lead day 1 to 9
NCEP GFSgfs2.40+0.17 · n=292.59+0.31 · n=282.77+0.50 · n=272.80+0.42 · n=262.95+0.29 · n=253.22+0.25 · n=243.33+0.22 · n=233.61+0.14 · n=223.64−0.04 · n=21NCEP GFS MAE by lead day 1 to 9
GraphCast (GFS init)graphcast_gfs2.19+0.18 · n=21.93+0.32 · n=1 GraphCast (GFS init) MAE by lead day 1 to 9
GraphCast (IFS init)graphcast_ifs2.29−1.27 · n=702.35−1.30 · n=692.40−1.29 · n=682.50−1.17 · n=682.60−1.21 · n=682.68−1.21 · n=672.87−1.22 · n=663.08−1.17 · n=653.41−1.37 · n=64GraphCast (IFS init) MAE by lead day 1 to 9
ECMWF IFS HRESifs_hres2.18−0.55 · n=292.28−0.33 · n=282.34−0.24 · n=272.61−0.03 · n=262.61−0.01 · n=252.68+0.17 · n=242.89+0.25 · n=233.02+0.21 · n=223.15−0.21 · n=21ECMWF IFS HRES MAE by lead day 1 to 9
Pangu-Weather (GFS init)pangu_gfs2.20+0.15 · n=22.20−0.13 · n=1 Pangu-Weather (GFS init) MAE by lead day 1 to 9
Pangu-Weather (IFS init)pangu_ifs2.30−0.99 · n=22.27−0.71 · n=1 Pangu-Weather (IFS init) MAE by lead day 1 to 9
Persistence (baseline)persistence2.43−0.05 · n=743.21−0.11 · n=743.50−0.18 · n=743.60−0.17 · n=743.68−0.18 · n=743.84−0.16 · n=743.96−0.17 · n=743.97−0.19 · n=744.16−0.25 · n=74Persistence (baseline) MAE by lead day 1 to 9

Where the errors are

Both maps show a fixed quantity per station. Neither shows which model wins where: on samples this short the per-station winner is mostly noise, and a map of winners would invite a comparison the data cannot carry.

ECMWF IFS HRES bias

Mean bias of the fixed reference model ECMWF IFS HRES (lead day 1, sampled daily minimum, 90d window, 12Z, bilinear). One model everywhere, so the colours compare stations, not models. Dot area grows with the number of scored days; fill is the mean bias (warm = model too warm, cool = too cold, grey = interval includes zero). The frame is a latitude/longitude graticule on an Albers projection.

Source: CastCheck · station coordinates NWS/NOAA · Albers conic projection · stations.csv. Hover a dot for its numbers.

model too cold interval includes zero model too warm dot area ∝ scored days

ECMWF IFS HRES bias as a table
StationModelMAE °FBias °Fn
KATL Atlanta HartsfieldECMWF IFS HRES2.10−1.7529
KAUS Austin BergstromECMWF IFS HRES2.65+2.0629
KBOS Boston LoganECMWF IFS HRES2.20−1.8126
KDCA Washington ReaganECMWF IFS HRES2.32−1.9029
KDEN Denver IntlECMWF IFS HRES2.70+0.9028
KDFW Dallas-Fort WorthECMWF IFS HRES1.70+1.4629
KEWR Newark LibertyECMWF IFS HRES2.04−1.1529
KIAH Houston BushECMWF IFS HRES1.67+0.4829
KLAS Las Vegas Harry ReidECMWF IFS HRES5.13−4.9528
KLAX Los Angeles IntlECMWF IFS HRES0.85−0.1228
KMIA Miami IntlECMWF IFS HRES2.59−2.3129
KMSP Minneapolis-St PaulECMWF IFS HRES1.75−1.3129
KMSY New Orleans IntlECMWF IFS HRES1.83+1.4929
KNYC New York Central ParkECMWF IFS HRES1.66−0.3029
KOKC Oklahoma CityECMWF IFS HRES4.17+3.4229
KORD Chicago O'HareECMWF IFS HRES1.69−1.3229
KPHL Philadelphia IntlECMWF IFS HRES2.81−2.5529
KPHX Phoenix Sky HarborECMWF IFS HRES2.97−1.2728
KSAN San Diego LindberghECMWF IFS HRES1.51−1.4728
KSAT San Antonio IntlECMWF IFS HRES1.42−0.4629
KSEA Seattle-TacomaECMWF IFS HRES1.60+0.1128
KSFO San Francisco IntlECMWF IFS HRES1.12−0.7128
KTTN Trenton MercerECMWF IFS HRES1.59+0.4729

All-model mean bias

Mean bias averaged over every scored model at each station (lead day 1, sampled daily minimum, 90d window, 12Z, bilinear). A station that is cold for all of them is a station property — elevation, coastline, a grid cell that is partly sea — not a model ranking. Dot area grows with the number of scored days; fill is the mean bias (warm = model too warm, cool = too cold). The frame is a latitude/longitude graticule on an Albers projection.

Source: CastCheck · station coordinates NWS/NOAA · Albers conic projection · stations.csv. Hover a dot for its numbers.

model too cold interval includes zero model too warm dot area ∝ scored days

All-model mean bias as a table
StationModelsMAE °FBias °Fn
KATL Atlanta Hartsfield11 models1.99−1.7470
KAUS Austin Bergstrom11 models3.58+3.3169
KBOS Boston Logan11 models2.30−2.1563
KDCA Washington Reagan11 models2.61−2.4970
KDEN Denver Intl11 models3.05+2.2368
KDFW Dallas-Fort Worth11 models1.52+0.3069
KEWR Newark Liberty11 models1.39−0.7770
KIAH Houston Bush11 models1.51+0.9570
KLAS Las Vegas Harry Reid11 models6.60−6.4668
KLAX Los Angeles Intl11 models1.50+0.2569
KMIA Miami Intl11 models1.52−0.2170
KMSP Minneapolis-St Paul11 models1.96−1.6570
KMSY New Orleans Intl11 models1.74−0.9670
KNYC New York Central Park11 models1.76−0.0770
KOKC Oklahoma City11 models2.89+2.4470
KORD Chicago O'Hare11 models1.53+0.2370
KPHL Philadelphia Intl11 models1.76−1.3570
KPHX Phoenix Sky Harbor11 models5.03−4.3469
KSAN San Diego Lindbergh11 models1.15−0.3169
KSAT San Antonio Intl11 models1.62−0.7570
KSEA Seattle-Tacoma11 models1.45−1.0769
KSFO San Francisco Intl11 models1.17−1.0569
KTTN Trenton Mercer11 models2.97+2.5670

Data availability

Each model is scored only over its own available period (2026-01-01 → 2026-08-30); the windows above are therefore not identical across models. Pairwise comparisons on the permanent-link pages use common days only.

ModelPeriodScored daysCoverage
ECMWF AIFS Single2026-08-02 → 2026-08-3029
2026-01-012026-08-30
Aurora (GFS init)2026-08-29 → 2026-08-302
2026-01-012026-08-30
Aurora (IFS init)2026-08-29 → 2026-08-302
2026-01-012026-08-30
FourCastNet v2 (GFS init)2026-08-29 → 2026-08-302
2026-01-012026-08-30
FourCastNet v2 (IFS init)2026-08-29 → 2026-08-302
2026-01-012026-08-30
NCEP GFS2026-08-02 → 2026-08-3029
2026-01-012026-08-30
GraphCast (GFS init)2026-01-02 → 2026-08-3036
2026-01-012026-08-30
GraphCast (IFS init)2026-01-02 → 2026-08-30197
2026-01-012026-08-30
ECMWF IFS HRES2026-08-02 → 2026-08-3029
2026-01-012026-08-30
Pangu-Weather (GFS init)2026-08-29 → 2026-08-302
2026-01-012026-08-30
Pangu-Weather (IFS init)2026-08-29 → 2026-08-302
2026-01-012026-08-30
Persistence (baseline)2026-01-01 → 2026-08-30215
2026-01-012026-08-30

Stations23

full station table
  • KNYC — New York Central Park
  • KEWR — Newark Liberty
  • KPHL — Philadelphia Intl
  • KTTN — Trenton Mercer
  • KBOS — Boston Logan
  • KDCA — Washington Reagan
  • KATL — Atlanta Hartsfield
  • KMIA — Miami Intl
  • KORD — Chicago O'Hare
  • KMSP — Minneapolis-St Paul
  • KDFW — Dallas-Fort Worth
  • KIAH — Houston Bush
  • KAUS — Austin Bergstrom
  • KSAT — San Antonio Intl
  • KMSY — New Orleans Intl
  • KOKC — Oklahoma City
  • KDEN — Denver Intl
  • KPHX — Phoenix Sky Harbor
  • KLAS — Las Vegas Harry Reid
  • KLAX — Los Angeles Intl
  • KSAN — San Diego Lindbergh
  • KSFO — San Francisco Intl
  • KSEA — Seattle-Tacoma