Moved from Ground Hornet.

This is without doubt V. acadica because of the very hairy tergum 2. V. vidua has almost no hairs on tergum 2. The brownish spots of tergum 2 are often absent in V. acadica workers. Great to have another image of this rarely photographed species!

I keep looking for those 2 brown spots that a forest yellowjacket should have when I'm in the field, and this one didn't have them.

Despite excellent quality of the picture, I feel quite uncomfortable to identify this worker at species level.
My first guess was a Ground Hornet, Vespula vidua. But ocular sinuses have only a narrow lower yellow stripe, instead of being entirely yellow. On the other hand, this feature is fairly variable in this group, especially among workers.
Although a Forest Yellowjacket (Vespula acadica) should have two reddish-yellow spots inside the black on her second urotergite, some of them have very small ones, and in this case, the left one COULD be concealed by the wings.
One on these two species, doubtless. But which one? I'm forced to give up, although I'm rather leaning for Vespula vidua.