I will say this about that 18z GFS run - that is one cold Canadian air mass near the end of that run, with temps in C Manitoba getting to -50°F to -55°F at night and not getting above -20°F for days at the beginning of March.
While we torch up here, down in Houston in the next couple of days they may break their all time low records, 5°F in 1930, and their low max of 20°F in 1899.
At hr60 and hr66 on the GFS @ 850 they are 4C and 7C warmer than the 12z Ukie @ hr66 and hr72, at least for my hood. We will see which is correct, if either .
What's interesting about the Ukie is that after that 0z warm burp run last night, it went back to what it had shown for the most part in the prior 4 runs.