Adult Steppe Gull (Larus (c.?) barabensis).
The primary pattern is towards the "light" end, having
black only to P4, but note that on P5 the black bleeds up the
outer edge (as on some cachinnans but not ponticus)
and lacks any paleness on the basal edge of this black (cach.
usually has some paler gray or whitish next ot the basal edge
of the black on P5 and P6). P9 lacks a mirror and the mirror on
P10 - while long - is separated from the white tip by a large
black band; most importantly (I feel), P8 lacks any form of gray
tongue intruding into the black along the inner side of the shaft
(such a tongue is evident on P7); on the underwing P10 has only
a small gray tongue on the inner web and P9 is extensively black.
Also note the thin, smudgy black subterminal band on the bill: