It’s only fitting that classical performers in the Juneau Jazz and Classics Festival improvise like their jazz counterparts. But Zuill Bailey wasn’t expecting that to happen with the concert schedule. Due to flight scheduling problems, two of the members of the Arianna String Quartet wound up stuck in St. Louis and didn’t make it in for two of the quartet’s scheduled performances on Monday night. So the two members who did arrive, teamed up with Zuill Bailey on cello, to form a trio. With only a half hour to learn new music, Bailey tells the story of how the ad hoc trio pulled off their one-of-a-kind performance.