do you know how long the tree has been dead? trees (certain species) can be slavaged for timber for many years after they die so long as insects and decay have not set in. Got some pic? how did it die? Lighting will cause decay from the inside even if you dont see any sign on the outside. Juglans nigra is a hearty species and can withstand alot of abuse from the elements and mother nature. If you just dont know cut a section and see if it has decent grain, texture, color, etc. if it has been dead a while you may not have to do any drying and can go ahead and start working it.