Part of the reason for the difference is that we are right on the edge of the storm over the next 24 hours. As can be seen in forecasts produced by the Short Range Ensemble Forecast system, more than 90% of the members call for at least 0.25" of SWE to fall over extreme northern Utah, southeast Idaho and western Wyoming, but the fraction of forecast members that call for that much precipitation drops off rapidly as one moves southward. The central Wasatch sit right in that dropoff area.
Through noon tomorrow, I'm inclined to lean toward the NAM, with periods of precipitation through noon tomorrow and accumulations of up to 6 inches in the upper elevations. Those hoping for more can always hope that the GFS turns out to be the model of choice, or that the high terrain around the Cottonwoods lights up the southwesterly flow more than either model indicates (it happens, but not all the time).
There's also the storms that will follow during the rest of the week. Keep your fingers crossed.