Light-rail service is coming to downtown St. Paul this summer, connecting with Minneapolis’ blue line on June 14. That’s a year ahead of the new Saints ballpark but just in time for the music. A block away from the green line’s final stop (at Union Depot) sits Mears Park, a hidden, tree-lined oasis amid Lowertown’s historic buildings that offers some of the best free outdoor concerts of summer. Foremost among them, the Twin Cities Jazz Festival arrives June 26-28 with its biggest lineup yet, featuring Branford Marsalis and Dianne Reeves. The Music in Mears series kicks off in early June with such local bands as Heiruspecs and Rogue Valley every Thursday, 6-9 p.m., through August. There’s also the folky Lowertown Roots Music Festival in late July, the eclectic Concrete & Grass Fest in early September and now a tentatively planned first-year blues bash. Even the parking is free — if you take the train.