Today is the closing day of the Medford Public Library’s third art exhibition at the new Charlotte & William Bloomberg Library building, a collection of watercolor paintings by Medford artist Katie Cornog. Cornog produces dynamic, colorful, contemporary watercolors with strong graphic compositions in a loose representational style. She has studied watercolor painting in the Boston area with several teachers, notably Gary Tucker, Marion Hall, Marjorie Glick and Karen Keough. Her library exhibition, featuring many Medford scenes, is on display in the second-floor gallery. In November and December, the library will show works by Medford painter Sarah Gerould.