I had snow for the first 2/3 of a mile or so, but after that it was snow free, including most of the Commons, since they were generally in sunshine. The snow seemed thin enough that the cars didn't compact it into a hard uncycleable layer, but not so thin that it disappeared immediately.
There were some icy patches near where the Tooting Bec Common cycle path joins up with Cavendish Road, but they were easily avoided, and bugger all further in towards central London.