Why do most online weather forecasts only state the chance of rain as a percantage, without stating the expected rainfall in millimetres? If there’s a 90% chance of rain, it matters a lot whether it will be 0.5 or 5mm
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Percentage refers to the entire forecast area. Volume can vary greatly from place to place within the forecast area.
Even as wrong as they often are, percentage is the more sensible forecast method that applies the the most people. I have a few friends with weather stations at their houses. We all live within 5 miles of each other. Even when we all get rain on the same days, we usually do not get the same amount.
I use the weather app Foreca. It uses localized forecast points and gives you the option to show volume instead of percentage. I prefer volume.
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