O SUSAN! The Houston Grand Opera is throwing a party this month for Texas-raised diva Susan Graham, celebrating her triumphant Houston (and world) debut as the hero in the HGO’s staging of the Handelian melodrama Ariodante in November. Where’s the shindig? Why, in the second act of Lehár’s Merry Widow. In a rare second appearance in the same town during the same season, the distinguished mezzo-soprano will bust out of her trouser-role typecasting and debut her version of Hanna, the wealthy, vivacious widow beset by gold diggers. But those serious Houston opera fans who regret the HGO’s substitution of the Viennese bonbon for the previously scheduled new operatic version of Dead Man Walking needn’t feel disappointed: Mid-month they can roll on over to the Capital City to see the Austin Lyric Opera production instead. Composer Jake Heggie’s eclectic score for Terrence McNally’s adaptation of the Sister Helen Prejean book vividly presents a musical drama of redemption. About the same time, the Dallas Opera offers up an international cast in Puccini’s final, unfinished masterpiece, Turandot, featuring the Southwest debut of a new ending by the notable Italian composer Luciano Berio. This will be a memorable month for Texas opera, indeed. (See Austin: Music/Dance; Dallas: Music/Dance; and Houston: Music/Dance.)