The last of the four jazz and blues concerts with Pat Loomis and his Friends completed a perfect run of outdoor music in Library Park where rain was but a distant memory. This was the fourth year of the concert series, sponsored jointly by the South End branch of the Boston Public Library and the Friends of the South End Library which received a generous donation for this purpose from the Ann H. Symington Foundation.Titled Let's Groove Tonight: A Funky Dance Party with Ivory Jones and White Chocolate, the event featured four vocalists, including a grandfather and son team, as well as the heart-rending Sarah Soulchild, whose powerful evocations of Janice Joplin could be heard on Tremont Street all the way down to Massachusetts Avenue.