(2 images) Herring Gull 2cy (argentatus), July 14 2003, Tampere, Finland (61.31N, 23.43E).

A 2cy argentatus. In many respects an average moult score for mid-July at Tampere. The complete moult is halfway with most wing-coverts and the inner primaries moulted to second generation. Primary P10 is still juvenile. P1-P6 are fully grown second generation flight-feathers; P7 is just shorter than P6. Note the narrow dark shaft-streaks and arrow-heads at P1-P3.
All median and greater coverts have been replaced, but a few juvenile wing-coverts are just visible in the upper row of lesser coverts. The fresh second generation coverts look very second generation like, being strongly barred. 
The open wing in the bottom image nicely illustrates the moult sequence of secondaries: the first replaced secondaries (S1) grow in at the division with the primaries, but soon the complete central secondary tract is dropped and will grow in simultaneously. Another moult wave is initiated at the tertials (which can be classified as secondaries as well) and the two waves meet at about secondaries #17.  

By July, the warm brown tones of the first moulted second generation feathers (inner greater coverts and inner median coverts) are faded to plain white, leaving a contrasting barred pattern on the wing-coverts. On average, 2cy argentatus is more contrastingly patterned than same aged 2cy argenteus, especially regarding the pattern on the central greater coverts. However, some argentatus are distinct "washed out" brown, showing the common vermiculated pattern of 2cy argenteus. 
The last moulted coverts are the central greater coverts and outer lesser coverts, replaced by mid-August. From mid-August onwards, 2cy argentatus start the partial autumn moult, starting again to drop the upper tertial and inner greater and median coverts. 

In the tables below, the primary moult scores of 2cy July argentatus in Finland can be read: