RadarNow! actually does show snow. It just doesn’t look the same as in other apps. Snow is just precipitation, so snow shows up in RadarNow! like any precipitation.
We get our radar imagery directly from NOAA’s radar stations. The differentiation between precipitation types is an artificial enhancement to the return. The radar beam itself reflects off of water molecules pretty much the same regardless of the state (solid, liquid).
Some displays provided by commercial weather sites show precipitation types during the winter month : rain, snow, mixed precipitations (sleet and freezing rain). This is not an analysis of the radar data itself but a post-treatment done with other data sources, the primary being surface reports (METAR).
While these displays look great, they are really interpretive results and are only as accurate as the algorithms used to create them. We choose to present the data in its raw form, without this processing so that our users get the most accurate and up to date imagery possible.
It is possible to tell where snow or frozen precipitation is likely falling. RadarNow! shows temperatures across the map in white ovals. If the temperature is below freezing, the precipitation is likely to be frozen.