Ah, you posted before my updated post made it through. If you look at the animation in the latter link which I added, you'll see it starts off in a very similar manner. If the Continental air feed is sustained, eventually everything below that dry layer becomes mixed, the whole lower airmass becomes cold, and then you have your classic cold spell. I've never looked at charts further north, so I don't know how rare or not it is up there - but down here that sort of thing is relatively common *if* you can get a proper Continental airmass.

It's also why in places like Yellowstone they get powder snow even at +7C - the cold wedge is very thick, and it's just the very lowest level which is warm, and even then the dewpoint is well below zero, hence the snow survives all the way down. I've heard you can even get snow at +10C, or 50F as they call it, out there. Of course here the sea does its best to ensure we seldom develop a Continental style airmass!

FWIW in "the Beast" we had a few hours of freezing rain as the Atlantic air moved back in. By then the cold layer was so dense, so thick, it took a while for it to be scrubbed away.

Originally Posted by: Retron