Scrub potatoes; pierce with a fork, and arrange in a circle on a paper towel in microwave oven. Microwave at HIGH 18 minutes, turning and rearranging potatoes halfway through cooking time. Cover and let stand 5 minutes. Let cool slightly. Cut unpeeled potatoes into 1/2-inch cubes.
Combine sour cream and next 4 ingredients in a large bowl, stirring until smooth. Add potato, green onions, celery, and blue cheese; toss gently to combine. Cover and chill at least 8 hours.