Several terms are used when talking about how much moisture is contained in a certain amount of snow. In our area, the most frequently used is liquid equivalent. This is the depth of water that would result from melting of a sample of snow. A rule of thumb says that for every 10 inches of snow you would have an inch of water. That 10-1 ratio only holds true when the snow is formed in the 34 to 28 degree Fahrenheit range. With warmer temperatures, as we’ve seen earlier this season the water content could be higher. In very cold temperatures, such as is the 14 to 10-degree range that may be a 30 to 1 ratio – where 30 inches of snow would be needed to get an inch of water. And the important temperature is the one at cloud height where the snow is forming. That’s why we take a sample of the snow and melt it to get the ACTUAL water equivalent.
Mary Knapp, Weather Data Library