What exactly does it mean when the weather bereau forecasts 50% rain. Does that mean 50% chance of rain in the marked area, or do they forecast rain in 50% of that area?
answer A VERY good question, and a question we get many times a month. In all essence, it means there is a 5 in 10 chance it will rain in the given area – it usually means in the entire area, but keep this in mind – thunderstorms are also qualitatively described – “isolated” and “scattered” – isolated meaning “here” and there” over a given area and “scattered” meaning more widely spread – so you could get a 20% chance of isolated showers meaning, a 2 in 10 chance of showers for that given day, but only “here and there”, whereas a 60% chance of scattered showers means a 6 in 10 chance it will rain and over a more widespread area. A 70% chance of showers (without a qualitative description) usually means a 7 in 10 chance it will rain over most of the area. Based on climatology (i.e. past weather events etc) a 6 in 10 chance means that for every time the weather conditions were similar, it rained 6 out of 10 times, hence 60% chance. • Sender’s name: m.santilhano (added 19OCT99) comments: P
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