Honest about how often we're right.

What we measure, and what good looks like

Four numbers per source. Each is colour-coded against what "good" actually means for that measure. They're deliberately different bars, because some things are much harder to forecast than others:

• Temperature error: the average gap between forecast and actual, in °C. Lower is better. Under 1° is good; the very best manage around half a degree. A score of 0.8° means the forecast was typically just under a degree off.
• Wind error: the average gap between forecast and actual wind speed, in km/h. Wind is locally gusty and harder to pin down, so under 5 km/h is good.
• Rain: every hour a forecast says rain (a 35% chance or more, the same line the app uses) or it says dry. So there are four outcomes: it said rain and it rained, it said rain and it didn't rain, it said dry and it stayed dry, or it said dry and it rained. Each card shows when it said rain, how often it rained (50%+ is good: a shower can miss you by a street) and when it said dry, how often it stayed dry. The rain deep dive has all four for every forecast.
• Rain score: the number that decides who is best at rain. The rain score counts all four rain outcomes above, and how sure the forecast was each time: a confident 90% chance of rain on a dry day costs far more than a cautious 40%. It is the average gap between the chance given and what happened, so lower is better and 0 would be perfect. A forecast can't game it by saying rain more often or by hardly ever saying it.
• Sky match: hour by hour, did the forecast's sky (fine / grey / wet) match what happened? This is the hardest call of the four: UK skies flip constantly and a category is either right or wrong, no partial credit. 70%+ is genuinely strong, and nobody on Earth gets 90% on this.

"Our blend" is the forecast the app actually shows you. It weighs the five sources by their proven track record at each measure and each time horizon, and re-weighs itself automatically as the scores evolve, so if one source goes off the boil, the blend leans away from it without anyone touching anything. The tick panel at the top tells you at a glance whether the blend is currently beating the individual forecasts.

What we use as ground truth

Rain is marked against real rain gauges. Each hour, each forecast is checked against the nearest Environment Agency tipping-bucket gauge within 10km (usually a few hundred metres away): did 0.2mm or more fall? A daily health check skips any gauge that looks blocked, stuck or out of line with its neighbours and the radar, and uses the next nearest. Where there is no gauge within 10km, the nearest Met Office station's report marks the rain instead. Gauges can't see drizzle under 0.2mm, so a drizzly hour can count as dry. Rain marking by gauge began on 30 September 2026, so rain covers fewer days than temperature.

Temperature, wind and sky are marked against Met Office observing stations, as a rain gauge measures only rain. We monitor a set of locations spread right across the UK, from the south coast to Edinburgh and Belfast, so the scores reflect performance nationally, not just one corner. The live league table marks things the same way.

What we're comparing

These scores compare the forecast data each provider sends us through their API, which is what our blend is built from. Providers' own apps may add things their APIs don't send, so this is a comparison of the feeds rather than of finished apps.

What we don't do

We don't cherry-pick. We don't drop bad runs. We don't weight scores by what makes any one source look better. By default we show every day we've scored since tracking began; you can narrow the window with a ?days=N URL parameter.