According to the U.S. Geological Survey (USGS.gov), the rule of thumb is that every inch of rain equals about 10 inches of snow.
While this rule of thumb is a reasonable average, keep in mind that the type of snow can make a huge difference in these numbers. For example very heavy snow may rise only 4 to 5 inches for that same single inch of water that falls.
To better picture the difference between types of snow, we can look at the water contents of very wet and very dry / powdery snow. 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 of water.
The National Weather Service Weather Forecast Office offers Tips for Measuring Snow.
Of course all the buzz right now, as CBS is reporting, is about Snow-vember: 9 states got hit early with a blast of wintry weather.