Score weather suitability for outdoor plans.
A single weather score is only useful if it tells you what would spoil the day, so this scores four factors separately and then weights them. Temperature carries the most weight because it dominates comfort, and it peaks near 20 C for active outdoor use, falling roughly five points for every degree either side. Rain probability is close to linear — nobody enjoys a 70% chance. Wind is free below about 10 km/h and then bites steeply, since a 40 km/h breeze ruins picnics, ball sports and paddling alike. UV is only penalised above index 3, the level at which protection starts to matter. The weakest of the four is reported on its own, because that is the factor you would actually plan around.
Weighted outdoor suitability score
Score = 0.35 x temperature score + 0.30 x rain score + 0.20 x wind score + 0.15 x UV score, where temperature score = 100 - 5 x |temp - 20|, rain score = 100 - 1.1 x rain%, wind score = 100 - 2.4 x (wind - 10) and UV score = 100 - 11 x (UV - 3)
Because outdoor plans usually involve moving. Metabolic heat during walking, cycling or sport adds the equivalent of several degrees, so an air temperature that feels slightly cool standing still is close to optimal once you are active.
The weakest factor. A score of 72 built on a 40% rain chance means something quite different from a 72 built on strong wind, and the mitigation is different too — a waterproof versus a sheltered venue.
Not directly. For cold days pair it with a wind chill calculation and for hot, humid days with an apparent temperature or heat index figure, since humidity can add ten degrees or more to how heat actually feels.