Not sure about 'operable' knocks, but I might need a bottle of Russian Standard to help me prepare for the 18Z; which, the way things seem to be headed, could be even more stonking!
The last one I can recall, was in February 1969: from light graupel with no wind, at 2C, to driving snow at -5C, all within about 30 minutes. I think that the pattern then was very similar to what the GFS is suggesting...Here's hoping!
You've answered your own question, I think...In Canada and the US, direct northerlies are hardly watered-down at all. The 'water' is either frozen, frozen and landlocked, or not there at all...
If there's one thing about the Sneck that I don't miss - it's those nagging, dreich Easterlies that keep day and night temperatures between 3 and 5C...I don't like them down here, either!
Well, if the Arctic sea-ice extended as far south (directly north of the UK) as Greenland does in the mid-Atlantic, you'd have a point??
Are we 'in danger' of wandering off-topic, CC?