We are -8 for the month, but normally you arrive there by being -16 and then normal over short periods. This has been essentially-7 to -10 each day, so nothing super cold.
To me, it's the shape of the ridge in the West. It's not been sharp S to N oriented so the cold hasn't been pressing south, more West to East. The GFS sharpens the Western Ridge and the cold crashes south.
It looks like some models got the qpf right but the thermals wrong at 850. The lighter qpf models look like they're missing but were better on thermals.
It looked like Maine or somewhere here in 1996. There was snow piled up to the bottom of stop signs and in mountains in parking lots from Early January until around Valentines Day.
The warm nose that Holston mentioned in a prior post is often a problem for valley areas. It tends to be more prevalent towards Nashville and from Chattanooga to Knoxville. In this case there's also a general lack of heavy precip on some modeling and that doesn't cool the column as efficiently.
The Rufus is similar, and a bit south with the snow line, to the other hi-res models. The Rufus is supposed to replace the NAM and NAM 3k at some point.
The Rufus has 1.5 inches across downtown Knoxville.
The 03z RAP looks similar to the 21z with a decent strip of 2-3 inches of snow in the same areas.
The RAP and HRRR are more stark with rain or snow vs freezing rain or mix.