Last June's season-ending performances of Leonard Bernstein's "West Side Story" by Michael Tilson Thomas and the San Francisco Symphony was a memorable occasion on several fronts - not merely a dynamic evening in Davies Symphony Hall but a bold claim for the musical brilliance of the score even in isolation from its theatrical trappings. Not that many of us needed convincing, mind you - the greatness of this music has never been in doubt. But the Symphony's new live recording (available on iTunes this week and on disc next month) brings it all back. To hear this recording is to marvel again at the rhythmic vivacity of Bernstein's writing, his extraordinary range of reference, and the way he adapts the various strains of midcentury American music to his creative vision without weakening their essential character. The orchestra sounds splendid, especially the percussion section, and the cast - led by the great Cheyenne Jackson as Tony - is almost uniformly strong. And "Somewhere," sung with limpid grace by soprano Julia Bullock (whose career has taken off since last year) sounds as beautiful as ever.