Here's my excruciatingly nerdy assessment ...
The pressure pattern at the larger synoptic scale observation shows that the high pressure over western and lower Ontario, behind the front, is actually the same as the pressure layout SE of the front associated with the WAR aspect. Normally that's consistent with a stationary front. However, there is a small gap where the boundary is geometrically biased N-W of that axis in between - hence the apparent N wind prior to the frontal arrival.
This gap will likely be were the front lays in and goes stationary...
Prior to that happening, there is a local pressure perturbation effect as Brian pointed out with the convection over lower Maine... it's giving the boundary a kind of meso scale momentum down the SE NH into NE Mass. It just means for eastern zones, the front arrives several hours earlier. By this evening, the front will likely be somewhere near the Pike... or whatever