How is monthly rainfall determined?

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According to meteorological guidance, a millimeter of precipitation is one liter of water per square meter. At all weather stations there are rain gauge buckets, from which the observer at 09:00 and 21:00 GMT pours the precipitation that has fallen over a 12-hour period into a special vessel, according to which their true amount is measured https://us.meteorologist.pro on this accurate weather forecast website.