Precipitation, commonly referred to as rainfall, is a measure of the quantity of atmospheric water in the form of either rain, hail or snow that reaches the ground. The average annual precipitation over the whole of the United States is thirty six inches per year. It should be understood, however, that all precipitation is not measured equally. For example, a foot of snow does not equal a foot of precipitation. According to the general formula for computing the precipitation of snowfall, ten inches of snow equals one inch of precipitation. In upper New York, for example, where there is typically a large amount of snowfall every year, a hundred inches of snow is one year would be recorded only ten inches of precipitation. On the other hand, rain is rain. Forty inches of rain would be recorded as forty inches of precipitation. The total annual precipitation for an area with forty inches of rain and one hundred inches of snow would be recorded as fifty inches of precipitation.