3k NAM was quite a bit further east than the 12k. It's going to be tough to really pull the full meat and potatoes of the midlevel banding far enough west.
Think you're dealing with RH w/ respect to ice vs water and how the sensors handle it. A brutally cold rad night isn't going to get you 100% RH. You'll start getting diamond dust with under 80% RH from the ASOS at like -35C or something.