If VWS is set to use Wx Station Predict, and snow is predicted, then you should be getting icon 17/18/19; not heavy rain.
Smart Forecast [SF] will not fix this, unless it's a very wet snow, and the bucket tips twice/15min, then you might be able to set a variable; which still may not work.
You could verify the prog is pointing to the correct icon though. Verify the icon. Or, Enable SF Override, then set a condition, like Temp <32 and choose the Snow in the right column pull-down. If it displays heavy rain, the correllation is dorked.
For learning about SF, try here.
http://www.wxforum.net/index.php?topic=2655.0