USGS= An inch of snow falling evenly on 1 acre of ground is equivalent to about 2,715 gallons of water. This figure, however, based upon the "rule-of-thumb" that 10 inches of snow is equal to 1 inch of water, can vary considerable, depending on whether the snow is heavy and wet, or powdery and dry. Heavy, wet snow has a very high water content—4 or 5 inches of this kind of snow contains about 1 inch of water. Thus, an inch of very wet snow over an acre might amount to more than 5,400 gallons of water, while an inch of powdery snow might yield only about 1,300 gallons.
NOAA = On average, thirteen inches of snow equals one inch of rain in the US, although this ratio can vary from two inches for sleet to nearly fifty inches for very dry, powdery snow under certain conditions.
NSIDC = The water content of snow is more variable than most people realize. While many snows that fall at temperatures close to 0 degrees Celsius (32 degrees Fahrenheit) and snows accompanied by strong winds do contain approximately one inch of water per ten inches of snowfall, the ratio is not generally accurate. Ten inches of fresh snow can contain as little as 0.10 inches of water and as much as 4 inches of water, depending on crystal structure, wind speed, temperature, and other factors. The majority of U.S. snows fall with a water-to-snow ratio of between 0.04 and 0.10.