We rarely get snow that stays more than a few hours in the lower elevations of the valley. The two areas that get snow that sticks around for a couple of months are the higher elevations in Lee Canyon where the ski resort is located and Kyle Canyon a few miles north of Lee Canyon both off of US 95. Red Rock state park at the west end of the valley sometimes gets snow when it rains in the lower elevation but most of the time the roads are clear as it goes away rapidly. That's probably the area with the steepest hills usable in the winter. You can also ride the River Mountain Trail at the east end of the valley and there are lots of roads in Henderson with some pretty challenging hills. Not quite like riding up to Mount Charleston but it should do.