Presspad #8: Frost Damage

It was a strange spring in the East: March was unseasonably warm, and then April was all-too-seasonably cold.  The result of these temperature ups and downs was frost damage to many fruit crops.  What is frost damage?  Is it permanent?  Is it fatal?  How did the grapes fare?  Why are temperatures that are harmless in February so dangerous in April?  What do we mean when we say that a vineyard has “50% damage?”  And, most importantly (for some of us, at least) what does this mean come harvest?