Q.graft a japanese weeping tree
Heavy snow buried my Japanese weeper. When snow thawed, I noticed the very tip was lopped off. Is it possible to salvage the head from where the branches sprout? It reached 3.5 feet and was blooming and growing beautifully last season. I love it and hope I can salvage it.

So sorry your weeping tree sustained a winter injury. When a tree has broken branches, the best course of action is to get the wound as neat and clean as you can. I would prune the injured area, if you have wiggle room to do so, so it is a clean cut.
You asked about grafting. You could attempt it with that broken branch via a whip graft but grafts aren't always successful and I feel that you really do not have to pursue that path. Your weeping cherry in its present state is salvageable. It will grow branches from the existing branches and will eventually fill in so you do not notice the injury zone.
For more information on grafting trees, please visit the following link:
http://www.extension.umn.edu/garden/yard-garden/fruit/grafting-and-budding-fruit-trees/