I use a big white plastic cutting board as my snowboard. It's heavy enough that it won't blow around, totally weatherproof, and won't warp. I've used it for several years for this. It's a flat cutting board, not the kind with the grooves for juice runoff.
If it wasn't windy, and my 4" gauge appears to have a similar amount to what fell, then I'll use that for water content, but most of the time I melt the core I take off my snowboard and use that. I don't think the 4" gauge is a good device for capturing snowfall if there is any wind at all, as the flakes are deflected around it.