Check if weather suits a picnic.
Four weather variables decide whether a picnic works, and they do not matter equally. Rain probability carries the heaviest weight because it is the only one that can end the event outright. Temperature comfort peaks around 23 C and falls away in both directions. Wind is underrated and becomes genuinely disruptive above about 12 km/h, when paper plates and tablecloths stop staying put. UV matters mainly above index 5, where shade becomes necessary rather than pleasant. Separately from comfort, the calculator flags food safety: perishable food is safe unrefrigerated for two hours, dropping to one hour above 32 C.
Suitability score
Score = 0.30 temperature + 0.35 rain + 0.20 wind + 0.15 UV
Food safety window
2 hours unrefrigerated, reducing to 1 hour at or above 32 C
General guidance only. Food safety timings are based on standard recommendations for the temperature danger zone but depend on how food was chilled and handled. Weather forecasts change — check conditions close to the time. For sun protection, follow current public health advice on UV exposure, shade and sunscreen use.
Because it is the only variable that can cancel the event rather than merely make it less pleasant. You can dress for cold, find shade for sun and shelter from wind, but a downpour ends an outdoor meal. Weighting it highest reflects how the decision actually gets made.
Two hours in normal conditions and only one hour once ambient temperature reaches 32 C, because bacterial growth accelerates sharply in the 5 to 60 C danger zone. Keep perishables in a cooler with ice packs until served, and discard anything left out beyond the window.