Fig 1) Yikes, it's a large first winter gull with a fair bit of white in the primaries. The bill is far too large for Thayer's; it's as long a Glaucous but with some gonydeal expansion as in Glaucous-winged. The amount of pink in the bill exceeds what is typical of Glaucous-winged, but it isn't as complete as on Glaucous.

Fig 2) The patterning in the primaries and the tertials point toward Glaucous Gull influence.

Fig 3) The flight feathers are rather uniform (as is the tail), which is to be expected in a cross with Glaucous-winged, but not in a cross with Herring Gull, where the outer primaries would contrast darker.