Not Yellowjackets !
Baldface Hornets !
Very dangerous !
Your picture is close enough to Identify on of the local scourges we have here.
I have a nest of them in the air space next to my stove pipe.
In the winter they get all toasty sometimes and climb down into the house,
they land on the woodstove and we find roasted hornets on the floor and the top of the stove.
Not fun to find with bare feet.
these are easily bigger than yellowjackets. and meaner.
Note that they have a heavier body than the yellowjacket and instead of a brownish head it is patterned.
The head is bigger as well.
These things are regular jackhammers with wings,
when they get fired up and will persue up to a half mile.
Wait 'til winter to get rid of these guys or you will be sorry.
http://unexco.com/gallery/hornets.html
Thom