Current model · uk-monotonic-calibrated-spatial-v2
Model statistics and validation
These results compare the calibrated model with the previous HadUK-derived probability on 2021–2024 cell-Christmas results. Those four years were held back until the promotion decision, then added when fitting the operational version.
Brier skill
+36.42%
Reduction in mean squared probability error.
Held-out results
151,980
37,995 linked cells across four later Christmases.
ROC–AUC
0.961
Unchanged from the incumbent after monotonic calibration.
Calibration error
6.92%
Down from 10.21%.
Overall comparison
Lower is better for Brier score, log loss and calibration error. Higher is better for ROC–AUC.
| Model | Brier | Log loss | ROC–AUC | Calibration error |
|---|---|---|---|---|
| Previous probability | 0.021683 | 0.130259 | 0.9606 | 10.21% |
| Current calibrated model | 0.013786 | 0.097197 | 0.9606 | 6.92% |
Results by region
Brier skill remained positive in every standard UK region.
| Region | Cells | Brier skill |
|---|---|---|
| Northern Ireland | +54.24% | |
| North West England | +53.55% | |
| Yorkshire and the Humber | +52.37% | |
| East Midlands | +50.27% | |
| East of England | +49.41% | |
| Wales | +46.84% | |
| West Midlands | +45.80% | |
| North East England | +41.17% | |
| South West England | +38.03% | |
| South East England | +35.14% | |
| London | +34.27% | |
| Scotland | +25.39% |
Spatial-block checks
The country was also divided into five broad geographic blocks. All five improved.
| Block | Cells | Brier skill |
|---|---|---|
| Block 1 | 7,560 | +30.67% |
| Block 2 | 9,430 | +37.64% |
| Block 3 | 8,849 | +27.61% |
| Block 4 | 5,103 | +47.03% |
| Block 5 | 7,053 | +47.08% |
What the scorecard covers
Primary test
HadUK reconstruction
The 151,980 results are reconstructed falling-snow events from daily HadUK temperature and rainfall. They are not 151,980 physical snow gauges.
Spatial check
Observed snow lying
Against the observed December snow-lying field, spatial rank correlation is 0.728 across 37,523 cells.
External check
GHCN-D stations
The supplementary station set contains 430 Christmas snow-depth reports from 21 merged UK sites. It is independent but geographically sparse.
See How it works for the full method and limitations, or return to the forecast.