Cherry trees, both ornamental and fruiting, are prone to fungal diseases. Since it has been a hot and then damp spring, I suspect this is what is happening. Go get the Bonide Fruit Tree Spray and sart spraying according to the schedule on the package. Next spring start in again with the spraying schedule. These disease are easier to prevent than cure. Check the base to make sure that you haven’t been piling mulch up against the bark. Piling mulch or dirt against the bark of the tree will slowly but surely kill the tree. Brush the mulch away from the trunk until you see the original soil level. Also watch for “suckers” of new shoots that will try to grow from the soil at the base of the tree. These are grafted trees and the root stock will always try to send up its own shoots. If you allow this, it robs energy from the upper part of the tree. Eventually the suckers take over and the “good” tree dies. Suckers may also form below the upper graft on the weeping cherry below the weeping part. This is the stem (yes, weeping cherries have 2 grafts…the root to the stem and the stem to the upper “weeping” part. These upper suckers must also be removed or the “weeping” branches will be cut off from nutrients and die.