How we keep score
Every morning we save each forecast's prediction for the next day in 30 UK towns. Once the official record is in, about five days later, we check what actually happened.
- Average miss on the high: how far each forecast's daytime high was from the real one. Lower is better.
- Rain called right: how often it correctly said whether there'd be rain (0.5 mm or more) or not.
- Closest on the day: how often it was the best forecast of the lot: right about rain, and nearest on temperature.
The record we check against is Open-Meteo's historical weather data, built on ECMWF's ERA5 reanalysis, the standard record weather scientists use. Because ERA5 is produced partly by ECMWF, it may give ECMWF's own forecast a slight home advantage, which is worth bearing in mind.