Thankfully has been used for centuries to mean ‘in a thankful manner,’ as in she accepted the offer thankfully. Since the 1960s, it has also been used as a sentence adverb to mean ‘fortunately,’ as in thankfully, we didn’t have to wait. Although this use has not attracted the same amount of attention as hopefully, it has been criticized for the same reasons. It is, however, far more common now than is the traditional use. For further explanation, see hopefully (usage) and sentence adverb.