Well there are a few ways to deal with this problem.
1) This one is the best because it is the most badass. Get a large propane tank for a grill and then get the attachment that is used to start fires. It looks like a flame thrower. Use this to melt the layers of snow and then let them freeze again. Repeat until perfect.
2) I use this one most often because it is easy to do. Stack up snow in the area that you want the jump and then lightly spray with water. You can use a spray bottle, your mouth, or what works best if you have one sitting around is a pump sprayer for a garden or a yard because it puts out a really nice fine mist (but it really doesnt matter that much).
3) I'm not sure where you live but when I lived in the land of 10,000 lakes it would usually get cold enough at night to freeze snow mounds that were sitting out. So I would just build my jump in the general shape that I wanted and let it sit. Usually by the morning it was good to go with a little sculpting.
Good luck man!
