How is the percentage of precipitation measured?

If I say that there are 50 percent chances that it will rain in this region tomorrow, what does it mean? Does it mean that it will rain on only half that region? Does it mean that it will rain only half that day? read more

If the forecaster is only 50% sure that precipitation will occur, and expects that, if it does occur, it will produce measurable rain over about 80 percent of the area, the PoP (chance of rain) is 40%. ( PoP = .5 x .8 which equals .4 or 40%. read more

The Precipitation Probability is given as a percentage (%) to the nearest 5% - which indicates how likely it is that any precipitation will fall during that period at the selected location. More precisely, by "any precipitation" we mean at least 0.1mm, which is about the smallest amount that we can measure. read more