FWIW, when I was on holiday several years ago in Yellowstone, I saw powdery snow falling at +9C (yes, really!) - the dewpoint would have been well below zero, as it's far above sea-level there.
It's as much to do with a low dewpoint as anything!
(FWIW, the 850s when that last lot of snow came through were -10C, but as we know that's associated with deep cold, rather than just a "tongue" of cold air at the lowest levels.)
Originally Posted by: Retron