The National Gridded Snowfall Analysis
estimates snowfall in the recent past by gathering
several operational data sets into a unified analysis. Snowfall observations are provided by numerous
observing networks, including ASOS, COOP, CoCoRaHS,
FAA, NWS spotters, and others.
The 24, 48, and 72 hour accumulations can also be browsed on an interactive map. (Look under the "Select Physical Element" dropdown for "SF Analysis" items.)
The climatological snowfall to liquid equivalent ratio (SLR) data used to generate the snowfall background (first guess) are available here.