Often times precipitation occurs in various forms. Sometimes it rains, other times it may snow or sleet.
Frozen precipitation is collected and then melted before being measured.
The density of liquid water remains constant. However, the density of frozen precipitation can vary greatly. Measuring the liquid equivalent of frozen precipitation can indicate the amount of water that fell, regardless of the type of precipitation. However, a heavy snow event may have a ratio of 3 or 4 inches of snow to 1 inch of water. Lighter snow can have a ratio of 20 inches of snow to 1 inch of water.