Article: In Norway, students having seen celebrations in Paris introduced Carnival processions, masked balls and Carnival balls to Christiana in the 1840s and 1850s. From 1863, the artist federation kunstnerforeningen held annual Carnival balls in the old Freemasons lodge, which inspired Johan Svendsens compositions "Norsk Kunstnerkarneval" and "Karneval in Paris". The following year, Svendsens Festpolonaise was written for the opening procession. Edvard Grieg attended and wrote "aus dem Karneval" (folkelivsbilleder Op. 19). Since 1988, the student organization Tårnseilerne has produced annual masquerade balls in Oslo, with masks, costumes and processions after attending an opera performance. The Carnival season also includes Fastelavens søndag (with cream buns) and fastelavensris with decorated branches.

Now answer this question: When do the processions occur after?
an opera performance