if it's an ensemble map (GEPS, GEFS, EPS), it's usually a mean or median. If it's coming from the parent (the CMC, the GFS, the EURO), it is verbatim showing what the model outputted. Different types of maps may result in slightly different outputs, as they use different formulas to decide how much snow has fallen (or stuck, in some cases)
sometimes i or others post percentile maps - those are also only for ensembles. These are like the confidence maps
I don't think it's that easy but I'm the wrong guy. I think they try and knock out these biases in subsequent updates but the best forecasters almost like to know the biases so they know how to correct or mentally adjust. YMMV - idk which biases are real these days
I think most of us would consider EURO king but GFS has it's days (yesterday). NAM did well yesterday too... some storms seem to work out better for the American suite of models then others. the GEM/CMC and UKIE are supposedly good models but maybe not for our specific purposes.