Quick update here before I try and get some sleep for the morning show (have to be in at 2:30 a.m.!). The 18z GFS has come in a hair colder and a bit closer to the 18z NAM. Still the models are different. The NAM is colder both in mid levels and in the boundary layer while the GFS is warmer in both locations. I’ve said all along that the finer resolution/mesoscale model NAM will have a better handle on the boundary layer conditions while the GFS should be superior in mid levels. Typically these SW Flow events tend to warm the mid levels a bit more than progged (their dynamic cooling is a bit overdone) so I like the GFS in this regard.
That said, now the GFS is a bit colder, I’m more confident in my snowfall predictions from earlier. Along the coast a warm boundary layer (thank strong easterly winds for this) should keep everything as rain unless we can evaporate quickly in the beginning and maybe pick up <1" of snow before it washes away in a deluge of rain. Further inland things are more complex. Boundary layer warmth isn't an issue initially so things will start as snow. The 18z GFS has about 0.15"-0.3" of liquid as all snow before the boundary layer starts to warm around MMK/DXR/IJD, and more than that for HFD/BDL before the mid levels warm first (then BL).
There is huge bust potential here since a delayed changeover by only 2 hours could mean the difference between 1″ of snow and 5″ of snow!! Take a look at the difference between the 12z GFS and the 18z GFS at BDL. By 12z tomorrow the 18z GFS has trended more the 2ºC colder in mid levels!! That’s a huge difference. In fact the 850mb-700mb thickness is nearly 10m lower in the new run. This could have major forecast implications if this colder trend comes to pass. In addition 3 hours of superb dendritic growth and extreme UVM will pile snow up quickly if temperatures are cold enough for all snow!
All in all I’m sticking with my previous call. Nothing on the coast, 1-3″ inland, 3-6″ in the hills, but I think the inland and hills COULD be in for a few surprises if this last minute “colder” trend materializes. Either way the morning commute looks messy!