Only went to Arrochar today so can tell you the road to Tarbet is fine now. It was slushy on the drive up, but on the way back it was +3 degrees, the snow had all melted on the roads and the wind had conpletely dried the road.
The Traffic Scotland website road cameras are good to check. The ones in Alexandria and Tyndrum give you a rough idea of the area.
http://trafficscotland.org