Answer: Based on your description it is possible that what you saw was a young Pawlonia tomentosa (Royal Pawlonia, Empress Tree) tree in bloom; it blooms before the leaves appear and the panicle can be a foot long and it does look like a plump bundle of grapes. Very striking!
Pawlonia will grow in zone 5, but it is not usually a recommended plant because it grows quickly to a large size and becomes a weak wooded tree. It is also capable of escaping from cultivation and colonizing areas in the wild, thus displacing our native plants. To give you an idea of its vigor, it has been used in strip mine reclamation and the paper industry.
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