Slice potatoes into 1/4-inch-thick slices; place in a large saucepan; add water to cover. Bring to a boil; cover, reduce heat, and simmer 15 minutes. Drain. Combine potato, green onions, and next 3 ingredients in a bowl; toss gently. Combine sour cream and remaining 5 ingredients in a small bowl; stir well. Pour dressing over potato mixture; toss gently. Cover and chill.