In a brief piece to camera that was posted on John Prine's YouTube channel Bob Weir spoke about Great Rain:

Hi, I'm Bobby Weir and I've been asked to name my favorite John Prine song and also why. And so my current favorite John Prine song is Great Rain and that's because he says he's gonna write a new verse for me and maybe even a bridge that he doesn't know about yet - because it doesn't get better than John Prine.