How Accurate Is a 14-Day Weather Forecast?

Forecast accuracy decays predictably. A 24-hour temperature forecast is right within a couple of degrees around 95% of the time. At 3 days it's roughly 90%. At 5 days about 80%. At 7 days it's near 70%, and by day 10-14 skill for specific rain timing falls close to climatology — the historical average for that date.

Why it decays The atmosphere is chaotic: tiny measurement errors double in size roughly every couple of days. Forecasters counter this with ensembles — running the model dozens of times with slightly nudged starting conditions. Where the runs agree, confidence is high; where they diverge, the forecast is a guess.

Reading a long-range forecast correctly At day 10 trust the trend, not the detail. "Warmer than average with unsettled spells" is a usable signal. "Rain at 3pm on the 14th" is not. For events, check again at day 5 and finalise at day 3.