Methodology: Total snowfall in an episode is an estimate of recent (24hr) actual snowfall plus predicted (48hr) new snow. Despite what you might expect, "actual" (past) snowfall has significant uncertainty. The U.S. National Weather Service API doesn't directly report recent snowfall totals, but does report "liquid equivalent precipitation". That's a number computed by collecting snow in tubes and then melting it, to see how much liquid-equivalent water it produces. That's related to snowfall but not in a straightforward way: 1) at colder temperatures, snow tends to be less dense, and 2) at higher wind speeds, more snow bypasses the NWS collection devices. This page implements corrections for both issues, but please note that it is not based on actual measured ground accumulation. The predicted portion also has uncertainty, but likely of a kind you already expect.