Having been there during this time of year, and living somewhat nearby I can tell you the weather is not THAT bad. Sure it was probably a bit worse than what we saw in GJ, but not by much. I doubt the precipitation fell as snow in the canyon - maybe on the rim way up above.
The storms tend to be isolated/scattered storms with pockets of sunshine elsewhere. It all depends on luck really, they could have missed the worst of it or been directly in the bulls-eye. Either way they are in an amazing place it would take a lot worse weather than this to ruin it.