Actual ratios of rain vs. snow depend upon several variables: how much moisture is available in the lower atmosphere and what the temperatures are at and above the surface. Twice per day, forecasters release weather ballons to collect data to determine things like moisture content and wind speeds with height in the lower part of the atmosphere. This data is put into what are called 'soundings'. These are very complicated, but essential to forecasting (especially for severe weather). Anyway, although this was slightly off the subject, it all means that 1" of rain does not always equal 10 or 12" of snow.
Thanks Iowa. I actually had that one too because the last link I put up actually came from this page, & all of these links may be interesting to some of us here. I never did order the book, but now that you reminded me it does look like an interesting read. http://www.nws.noaa.gov/om/snowpln.htm